Greenhouse Pest Management 9781774074534, 9781774072202, 1774072203, 1774074532

Table of contents :
Cover......Page 1
Title Page......Page 5
Copyright......Page 6
ABOUT THE EDITOR......Page 7
TABLE OF CONTENTS......Page 9
List of Figures......Page 15
List of Tables......Page 21
Preface......Page 23
Introduction......Page 25
Chapter 1 Introduction to Greenhouses......Page 27
1.1 History......Page 28
1.2 Introduction......Page 30
1.4 Advantages......Page 32
1.5 Classification......Page 33
Chapter 2 Identification of Pests......Page 43
2.1 Introduction......Page 44
2.2 Aphids......Page 45
2.3 Broad Mites......Page 46
2.4 Caterpillars......Page 48
2.5 Cyclamen Mites......Page 49
2.6 Fungus Gnats......Page 50
2.7 Leaf Hoppers......Page 51
2.8 Leaf Miners......Page 52
2.9 Mealybugs......Page 53
2.11 Scales......Page 55
2.13 Slugs And Snails......Page 57
2.14 Twospotted Spider Mite......Page 58
2.15 Western Flower Thrips......Page 59
2.16 Whiteflies......Page 61
Chapter 3 Viral Diseases......Page 63
3.2 Dispersal Mechanisms......Page 64
3.3 Infection Sources......Page 65
3.4 Transmission of Viral Diseases......Page 66
3.5 Major Viral Diseases......Page 67
3.6 Plant Virus Control......Page 81
Chapter 4 Bacterial And Fungal Diseases......Page 83
4.2 Bacterial Diseases......Page 84
4.3 Fungal Diseases......Page 88
Chapter 5 Nematodes......Page 107
5.2 Biology of Nematode Pests......Page 108
5.4 Monitoring......Page 109
5.5 Strategies For Control......Page 111
5.6 Integrated Approach......Page 114
Chapter 6 Epidemiology......Page 115
6.2 Disease/Pest Tetrahedron......Page 116
6.3 Epidemics......Page 119
6.4 Damage......Page 120
6.5 Action Thresholds......Page 121
6.6 Relationships And Thresholds......Page 122
6.7 Research......Page 123
6.8 Integrated Control......Page 124
Chapter 7 Sampling......Page 127
7.2 Insects......Page 128
7.3. Pathogens......Page 134
Chapter 8 Monitoring......Page 139
8.1 Scouting......Page 140
8.2 Passive Scouting......Page 141
8.3 Active Scouting......Page 142
8.4 Thresholds......Page 143
8.5 A Recent Application of Lighting And Pests......Page 145
Chapter 9 Sanitation And Cultural Control......Page 147
9.4 Sanitation......Page 148
Chapter 10 Use of Pesticides......Page 151
10.1 Introduction......Page 152
10.4 Coverage of Pesticides......Page 153
10.5 Timing......Page 154
10.6 Water Quality......Page 155
10.7 Modes of Action......Page 156
10.10 Label Rate......Page 157
10.12 Frequency......Page 158
10.13 Issues With Using Peticides......Page 159
10.15 Biological Factors......Page 161
10.16 Multiple Pests......Page 165
10.17 Mixture of Pesticides......Page 166
Chapter 11 Biological Control......Page 169
11.2 Advantages......Page 170
11.3 QC......Page 171
11.4 Implementation......Page 174
11.5 Approaches......Page 175
11.6 Natural Enemies And Their Types......Page 176
11.7 Banker Plants......Page 179
11.8 Effect Of Environment......Page 181
11.9 Effect Of Plants......Page 182
11.10 Release Of Natural Enemies......Page 184
11.11 Pesticides......Page 185
Chapter 12 Management of A Greenhouse......Page 187
12.2 Management......Page 188
12.3 Crop Management......Page 198
12.4 Crop Environment And Management......Page 202
Chapter 13 Host and Plant Resistance......Page 209
13.2 Key Terminology......Page 210
13.3 Mechanisms of Resistance......Page 211
13.4 Genetics......Page 213
13.5 Durability......Page 214
13.6 Breeding......Page 215
13.7 Strategies......Page 219
13.8 Advantages and Disadvantages......Page 220
13.9 Current Scenario......Page 221
13.10 Perspectives......Page 222
Chapter 14 Disinfestation......Page 223
14.2 Steaming......Page 224
14.3 Fumigation......Page 225
14.5 Side-Effects......Page 227
14.6 Tests......Page 228
14.7 Effect of Chemical Pesticides on Useful Organisms......Page 230
14.8 Factors Involved......Page 231
14.9 Pesticide Resistance And Anti-Resistance......Page 233
Chapter 15 Common Pests......Page 237
15.2 Pink Hibiscus Mealybug......Page 238
15.3 Chilli Thrips......Page 240
15.4 Leafminer......Page 242
15.5 Two-Spotted Spider Mites......Page 245
15.6 Fungus Gnats......Page 247
15.7 Shore Flies......Page 249
15.8 Whiteflies......Page 250
15.9 Aphids......Page 251
15.10 Thrips......Page 254
15.11 Scales......Page 255
15.12 Identification......Page 257
Chapter 16 Common Greenhouse Crops and Pest Management......Page 275
16.2 Major Pests......Page 276
16.3 IPM......Page 277
16.4 Cucurbits......Page 279
16.5 Strawberries And Greenhouses......Page 283
References......Page 285
Index......Page 295
Back Cover......Page 300

Citation preview

GREENHOUSE PEST MANAGEMENT

GREENHOUSE PEST MANAGEMENT

Edited by: Laichattiwar Mukesh Anandrao

www.delvepublishing.com

Greenhouse Pest Management Laichattiwar Mukesh Anandrao Delve Publishing 2010 Winston Park Drive, 2nd Floor Oakville, ON L6H 5R7 Canada www.delvepublishing.com Tel: 001-289-291-7705 001-905-616-2116 Fax: 001-289-291-7601 Email: [email protected] e-book Edition 2020 ISBN: 978-1-77407-453-4 (e-book) This book contains information obtained from highly regarded resources. Reprinted material sources are indicated and copyright remains with the original owners. Copyright for images and other graphics remains with the original owners as indicated. A Wide variety of references are listed. Reasonable efforts have been made to publish reliable data. Authors or Editors or Publishers are not responsible for the accuracy of the information in the published chapters or consequences of their use. The publisher assumes no responsibility for any damage or grievance to the persons or property arising out of the use of any materials, instructions, methods or thoughts in the book. The authors or editors and the publisher have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission has not been obtained. If any copyright holder has not been acknowledged, please write to us so we may rectify. Notice: Registered trademark of products or corporate names are used only for explanation and identification without intent of infringement. © 2020 Delve Publishing ISBN: 978-1-77407-220-2 (Hardcover) Delve Publishing publishes wide variety of books and eBooks. For more information about Delve Publishing and its products, visit our website at www.delvepublishing. com.

ABOUT THE EDITOR

Dr. Mukesh Laichattiwar, Ph. D (Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, U.P.) is presently working as Assistant Professor at College of Agriculture, Parul University, Vadodara. Dr. Laichattiwar worked as Assistant Professor at college of Agriculture, Naigaon (Bz.), Nanded M.S. (2018-2019). He did his B.Sc (Ag.) From College of Agriculture, Ambajogai (Vasantrao Naik Marathwada Krishi Vidyapeeth, Parbhani, M.S.) and M.Sc (Ag.) from Institute of Agricultural Sciences, Banaras Hindu University,Varanasi, U.P., He was awarded UGC fellowship for his Ph. D research. He qualified ICAR-NET in 2013. Dr. Laichattiwar is a recipient of Best Poster presentation award in 2014. He Published 18 research article, 7 book chapters/proceedings, 5 popular articles and 15 abstract.

TABLE OF CONTENTS

List of Figures ..............................................................................................xiii List of Tables................................................................................................ xix Preface........................................................................................................ xxi Introduction........................................................................ .................. ....xxiii Chapter 1

Introduction to Greenhouses .................................................................... 1 1.1 History................................................................................................. 2 1.2 Introduction ......................................................................................... 4 1.3 Greenhouse Effect................................................................................ 6 1.4 Advantages .......................................................................................... 6 1.5 Classification ....................................................................................... 7

Chapter 2

Identification of Pests.............................................................................. 17 2.1 Introduction ....................................................................................... 18 2.2 Aphids ............................................................................................... 19 2.3 Broad Mites ....................................................................................... 20 2.4 Caterpillars ........................................................................................ 22 2.5 Cyclamen Mites ................................................................................. 23 2.6 Fungus Gnats ..................................................................................... 24 2.7 Leaf Hoppers ..................................................................................... 25 2.8 Leaf Miners ........................................................................................ 26 2.9 Mealybugs ......................................................................................... 27 2.10 Pillbugs and Sowbugs ...................................................................... 29 2.11 Scales .............................................................................................. 29 2.12 Shore Flies ....................................................................................... 31 2.13 Slugs And Snails .............................................................................. 31 2.14 Twospotted Spider Mite.................................................................... 32 2.15 Western Flower Thrips...................................................................... 33

2.16 Whiteflies ........................................................................................ 35 Chapter 3

Viral Diseases .......................................................................................... 37 3.1 Introduction ....................................................................................... 38 3.2 Dispersal Mechanisms ....................................................................... 38 3.3 Infection Sources ............................................................................... 39 3.4 Transmission of Viral Diseases ............................................................ 40 3.5 Major Viral Diseases .......................................................................... 41 3.6 Plant Virus Control ............................................................................. 55

Chapter 4

Bacterial And Fungal Diseases................................................................. 57 4.1 Introduction ....................................................................................... 58 4.2 Bacterial Diseases .............................................................................. 58 4.3 Fungal Diseases ................................................................................. 62

Chapter 5

Nematodes .............................................................................................. 81 5.1 Introduction ....................................................................................... 82 5.2 Biology of Nematode Pests ................................................................ 82 5.3 Symptoms .......................................................................................... 83 5.4 Monitoring......................................................................................... 83 5.5 Strategies For Control ......................................................................... 85 5.6 Integrated Approach .......................................................................... 88

Chapter 6

Epidemiology........................................................................................... 89 6.1 Introduction ....................................................................................... 90 6.2 Disease/Pest Tetrahedron.................................................................... 90 6.3 Epidemics .......................................................................................... 93 6.4 Damage ............................................................................................. 94 6.5 Action Thresholds .............................................................................. 95 6.6 Relationships And Thresholds............................................................. 96 6.7 Research ............................................................................................ 97 6.8 Integrated Control .............................................................................. 98

Chapter 7

Sampling ............................................................................................... 101 7.1 Introduction ..................................................................................... 102 7.2 Insects ............................................................................................. 102 7.3. Pathogens ....................................................................................... 108 viii

Chapter 8

Monitoring ............................................................................................ 113 8.1 Scouting .......................................................................................... 114 8.2 Passive Scouting............................................................................... 115 8.3 Active Scouting ................................................................................ 116 8.4 Thresholds ....................................................................................... 117 8.5 A Recent Application of Lighting And Pests ...................................... 119

Chapter 9

Sanitation And Cultural Control ............................................................ 121 9.1 Introduction ..................................................................................... 122 9.2 Irrigation .......................................................................................... 122 9.3 Fertility ............................................................................................ 122 9.4 Sanitation ........................................................................................ 122

Chapter 10 Use of Pesticides ................................................................................... 125 10.1 Introduction ................................................................................... 126 10.2 Improving Performance.................................................................. 127 10.3 Identification of Pests ..................................................................... 127 10.4 Coverage of Pesticides ................................................................... 127 10.5 Timing ........................................................................................... 128 10.6 Water Quality ................................................................................ 129 10.7 Modes of Action ............................................................................ 130 10.8 Application Technique ................................................................... 131 10.9 Targets .......................................................................................... 131 10.10 Label Rate.................................................................................... 131 10.11 Shelf Life...................................................................................... 132 10.12 Frequency .................................................................................... 132 10.13 Issues With Using Peticides .......................................................... 133 10.14 Operational Factors ..................................................................... 135 10.15 Biological Factors ........................................................................ 135 10.16 Multiple Pests .............................................................................. 139 10.17 Mixture of Pesticides .................................................................... 140 Chapter 11 Biological Control ................................................................................. 143 11.1 Introduction ................................................................................... 144 11.2 Advantages .................................................................................... 144 11.3 QC ................................................................................................ 145 ix

11.4 Implementation ............................................................................. 148 11.5 Approaches.................................................................................... 149 11.6 Natural Enemies And Their Types ................................................... 150 11.7 Banker Plants ................................................................................. 153 11.8 Effect Of Environment .................................................................... 155 11.9 Effect Of Plants .............................................................................. 156 11.10 Release Of Natural Enemies......................................................... 158 11.11 Pesticides ..................................................................................... 159 Chapter 12 Management of A Greenhouse .............................................................. 161 12.1 Introduction ................................................................................... 162 12.2 Management.................................................................................. 162 12.3 Crop Management ......................................................................... 172 12.4 Crop Environment And Management ............................................. 176 Chapter 13 Host and Plant Resistance ..................................................................... 183 13.1 Introduction ................................................................................... 184 13.2 Key Terminology ............................................................................ 184 13.3 Mechanisms of Resistance ............................................................. 185 13.4 Genetics ........................................................................................ 187 13.5 Durability ..................................................................................... 188 13.6 Breeding ........................................................................................ 189 13.7 Strategies ....................................................................................... 193 13.8 Advantages and Disadvantages ...................................................... 194 13.9 Current Scenario ............................................................................ 195 13.10 Perspectives ................................................................................. 196 Chapter 14 Disinfestation ........................................................................................ 197 14.1 Introduction ................................................................................... 198 14.2 Steaming........................................................................................ 198 14.3 Fumigation .................................................................................... 199 14.4 Importance of Selective Pesticides ................................................. 201 14.5 Side-Effects .................................................................................... 201 14.6 Tests ............................................................................................... 202 14.7 Effect of Chemical Pesticides on Useful Organisms ........................ 204 14.8 Factors Involved ............................................................................. 205 x

14.9 Pesticide Resistance And Anti-Resistance ....................................... 207 Chapter 15 Common Pests....................................................................................... 211 15.1 Introduction ................................................................................... 212 15.2 Pink Hibiscus Mealybug ................................................................ 212 15.3 Chilli Thrips ................................................................................... 214 15.4 Leafminer ...................................................................................... 216 15.5 Two-Spotted Spider Mites............................................................... 219 15.6 Fungus Gnats ................................................................................. 221 15.7 Shore Flies ..................................................................................... 223 15.8 Whiteflies ...................................................................................... 224 15.9 Aphids ........................................................................................... 225 15.10 Thrips........................................................................................... 228 15.11 Scales .......................................................................................... 229 15.12 Identification ............................................................................... 231 Chapter 16 Common Greenhouse Crops and Pest Management.............................. 249 16.1 Introduction ................................................................................... 250 16.2 Major Pests .................................................................................... 250 16.3 IPM................................................................................................ 251 16.4 Cucurbits ....................................................................................... 253 16.5 Strawberries And Greenhouses ...................................................... 257 References............................................................................................. 259 Index ..................................................................................................... 269

xi

LIST OF FIGURES Figure 1. Typical plastic green house Figure 1.2 Greenhouse hoods with pots Figure 1.3 Greenhouse –Rigid panel Figure 1.4 Greenhouse –Plastic film Figure 1.5 Greenhouse –Glass Figure 1.6 Greenhouse – Truss framed Figure 1.7 Greenhouse – pipe framed Figure 1.8 Greenhouse – wooden framed Figure 1.9 Greenhouse – Quonset Figure 1.10 Greenhouse – Saw tooth Figure 1.11 Greenhouse – Ridge and furrow Figure 1.12 Greenhouse – Lean-to Figure 2.1 Aphids Figure 2.2 Broad mites Figure 2.3 Caterpillars Figure 2.4 Cyclamen mites Figure 2.5 Fungus Gnats Figure 2.6 Leaf hoppers Figure 2.7 Leaf miners Figure 2.8 Mealy bugs Figure 2.9 Pill bugs and sow bugs Figure 2.10 Scales Figure 2.11 Shore flies Figure 2.12 Slugs and snails Figure 2.13 Twospotted spider mice Figure 2.14 Western flower thrips

xiii

Figure 2.15 White flies Figure 3.1 Cucumber Mosaic Viruses Figure 3.2 Potyvirus Figure 3.3 Luteovirus Figure 3.4 Tomato yellow leaf curl virus Figure 3.5 Clostero virus Figure 3.6 Tomato spotted wilt virus Figure 3.7 Squash Mosaic Virus Figure 3.8 Melon Necrotic Spot Virus Figure 3.9 Tobamoviruses Figure 4.1 Tomato Bacterial Canker Figure 4.2 Tomato soft rots Figure 4.3 Bacterial blight Figure 4.4 Angular leaf spots Figure 4.5 Phytophthora and Pythium Rots Figure 4.6 Rhizoctonia Stem Rot Figure 4.7 Corky Root Rot Figure 4.8 Crown and root rot Figure 4.9 Black Root Rot Figure 4.10 Fusarium Wilt Figure 4.11 Verticllium-Philaphora Wilt Figure 4.12 Powdery Mildews Figure 4.13 Downy Mildews Figure 4.14 Botrytis Figure 4.15 Sclerotina Rot Figure 4.16 Tomato Early Blight Figure 4.17 Didymella Figure 4.18 Rust Figure 4.18 Cucurbit scab Figure 6.1 Disease/pest tetrahedron Figure 14.1 Sequential procedures

xiv

Figure 15.1 Pink Hibiscus mealybug Figure 15.2 Pink Hibiscus mealybug-Damage Figure 15.3 Chilli thrips Figure 15.3 Chilli thrips Figure 15.4 Deformed pepper fruit Figure 15.5 Feeding scars Figure 15.6 Leafminer Figure 15.7 Leafminer - Adult Figure 15.8 Leafminer - Larva Figure 15.9 Leafminer - Larva Figure 15.10 Leafminer - Adult Figure 15.11 Leafminer – Tunneling damage Figure 15.12 Two spotted spider mite Figure 15.13 Two spotted spider mite-Damage Figure 15.14 Two spotted spider mite-Stippling Figure 15.15 Two spotted spider mite-Webbing Figure 15.16 Two spotted spider mite-Blotchy appearance Figure 15.17 Fungus Gnats Figure 15.18 Fungus Gnats- Damaged plant Figure 15.19 Fungus Gnats- Tunneling in the stem Figure 15.20 Shore flies- Larva Figure 15.21 Shore flies- Adults Figure 15.22 White flies- Adults Figure 15.23 White flies- Pupa (Silver leaf) Figure 15.24 White flies- Pupa (Greenhouse) Figure 15.25 Aphids Figure 15.26 Aphids-Tail pipes Figure 15.27 Aphids-Rose buds Figure 15.28 Aphids-Underside of leaf Figure 15.29 Aphids-Immature Figure 15.30 Aphids- Sooty mold Figure 15.31 Thrips xv

Figure 15.32 Thrips-Damage(Peony) Figure 15.33 Thrips-Damage Figure 15.34 Scales-Hemispherical Figure 15.35 Scales-Florida red scale Figure 15.36 Scales-Cactus Figure 15.37 Scouting-Yellow sticky cards Figure 15.38 Scouting-Pests on Yellow sticky cards Figure 15.39 Scouting-Used in retail greenhouses Figure 15.40 Magnification Figure 15.41 Vertical placement of sticky cards Figure 15.42 Horizontal placements of sticky cards Figure 15.43 Winged adult aphid on sticky cards Figure 15.44 Thrips on sticky cards Figure 15.45 Fungus gnat Vs Midges Vs Aphid on sticky cards Figure 15.46 Fungus gnat Vs whiteflies on sticky cards Figure 15.47 Adult Fungus gnat on sticky cards Figure 15.48 Fungus gnat on potato slices Figure 15.49 Fungus gnat and Shorefly Figure 15.50 Shoreflies on Algae Figure 15.51 Shorefly-Adult Figure 15.52 Leafminer-Adult Figure 15.53 Leafminer-mines Figure 15.54 Shoreflies-fecal dropping Figure 15.55 Leafhopper Figure 15.56 Leafhopper-Adult Figure 15.57 Thrips-Adult Figure 15.58 Whiteflies Figure 15.59 Whiteflies-Adult Figure 15.60 Banded winged Whitefly-Adult Figure 15.61 Greenhouse Whitefly-Pupal stage Figure 15.62 Sweet potato Whitefly-Pupal stage Figure 15.63 Parasitic wasp xvi

Figure 15.64 Encarsia formosa-Quality control Figure 15.65 Encarsia formosa-Adult Figure 15.66 Eretmocerous- Quality control Figure 15.67 Eretmocerous Vs Encarsia- Quality control Figure 15.68 Eretmocerous Vs Thrips- Quality control Figure 15.69 Shorefly parasitoid Figure 15.70 Fungus Gnat parasitoid Figure 15.71 Hunter flies Figure 15.72 Hunter flies-Adult Figure 15.73 Hunter flies-Shiny wings without spots Figure 15.74 Shoreflies Vs Hunter flies Figure 15.75 Hover flies Figure 15.76 Fungus gnat Vs Midge Figure 15.77 Midge-Adults Figure 15.78 Moth Figure 15.79 Shorefly Vs Mothflies Figure 16.1 Flow diagram Figure 16.2 Greenhouse grown tomatoes Figure 16.3 Greenhouse grown cucumbers Figure 16.4 Infection due to spider mite Figure 16.5 Downy mildew Figure 16.6 Grey mould Figure 16.7 Gummy stem blight Figure 16.8 Pythium root and stem base rot Figure 16.9 Cucumber Mosaic Virus Figure 16.10 Cucumber Mosaic Virus Figure 16.11 Lepidopteran pests of strawberries Figure 16.12 Aphid pests of strawberries Figure 16.13 Root Weevils pests of strawberries

xvii

LIST OF TABLES Table 1.1 Estimated utilization of plastic Greenhouse Table 8.1 List of Biological control agents Table 8.2: Light and connection with insects

PREFACE

The concept of greenhouses has been an interesting since decades as they provide an excellent base for cultivators who wish to go for mass scale vegetation under controlled conditions. This book will give an impetus towards initiating integrated pest management. The pests have been proved as a crucial factor in management of greenhouses. Many techniques were used since many areas to produce crops which can be freed of pests and pathogens but of often landed in several roadblocks. Today’s technology may decide the advancements in the future. The same concept can be applied to the greenhouse and integrated pest management. Several attempts to adapt crop production according to the manipulated environment date back to previous times. The structures which were used in protected crop production was reported first in the early Roman empire and the Emperor Tiberius Caesar (14-37 AD) initiated this. These structures contained mobile beds in which cucumbers where placed when the weather was bad and placed outside in the case of good weather. The greenhouses in UK used glass structures which were built to cultivate plants imported from America and tropical Asia during 16th and 17th century. These important methods ceased to function with the decline of the Roman Empire. In early 18th century there was much development in this field which has flourished since then. Simple forms of greenhouses were first seen in England, Japan, China, France and The Netherlands. In the late 19th century there was a drastic development in the commercial production in the greenhouses. The primary purpose of growing crops under protected conditions such as greenhousse is to enhance their cropping season and to protect the crop from rough environmental conditions. The extreme conditions can be diseases, precipitation and temperatures. This book has taken care of almost all the aspects of the greenhouse and the process of associated integrated pest management. This book may be used as a hand book for undergraduates, postgraduates and research students who would like to know the basics and would like to excel in the field of integrated pest management in greenhouses.

INTRODUCTION

Due to active international trade in flowering plants and ornamentals there has been an extensive spread of pests and diseases all around the world. In Europe alone, about 40 new varieties of pests were found in the protected crops in the last two decades. The enhancing complexity of the pests had left the producers with mayhem and extreme measures were initiated. This has resulted in production of resistant varieties which made the growers to follow the regimes of integrated pest management (IPM). Once pesticide resistance increases, there will be more spread of resistant varieties and this would become a severe problem for communities that depend on the greenhouses. Much more advanced integrated systems of greenhouse pest and control of disease was developed in Northern Europe and also in Canada. This practice of using IPM has always been a tedious and cumbersome process as far as economics and manual labor are concerned. Initially in the late 50s there was a spread of the greenhouses which were mostly focused on vegetable production. Once the demand for ornamental plant and cut-flower industries developed there was a huge demand in UK and The Netherlands. In 1960, The Netherlands had the highest number of greenhouse grown crops which ranged from about 75% of all the tomatoes grown in that country. The UK had about 2000 hectares of the greenhouse in the same period. This shows that we are bounded with protected crops. In 1980, about 1,50000 hectares of greenhouses were installed worldwide that produced high-value crops. In the year 1995, there was an increase in the area of the greenhouse installations which amounted to about 2,80,000 hectares. This book presents the various types of pests and regulatory mechanisms involved in the process of integrated pest management in a greenhouse.

CHAPTER 1

INTRODUCTION TO GREENHOUSES

CONTENTS 1.1 History................................................................................................. 2 1.2 Introduction ......................................................................................... 4 1.3 Greenhouse Effect................................................................................ 6 1.4 Advantages .......................................................................................... 6 1.5 Classification ....................................................................................... 7

2

Greenhouse Pest Management

1.1 HISTORY A green house is a structure which is inflated or framed and it can be enclosed with either translucent or transparent material. Crops can be grown under partially controlled environment in a greenhouse and they have large space which can accommodate persons to perform tasks within it and other relevant operations. In the first century, Emperor Tiberius allowed growing of cucumbers off-season beneath a transparent stone and as per the evidences found, it can be taken as the first ever protected agriculture in the human history. This type of technology was sparingly used in the following 1500 years. Hot beds, bell jars and glass lanterns were used to save the horticultural crops in cold seasons during 16th century. Portable frame made up of wood and enclosed with translucent paper which was oiled was used to heat the interior environment.

Figure 1.1: Typical plastic green house. Source: https://www.elloughton-greenhouses.co.uk/information/news/how-todismantle-a-greenhouse

Straw mats and oil paper were used to save the crops from extreme environmental conditions. The green houses in England and France were

Introduction to Greenhouses

3

heated with the help of manure covered with panes made up of glass. The first greenhouse of its kind during 1700s utilized glass as a sloping roof and it was only on one side. After some years in the same century, the utility of glass was extended to both sides. Glasshouses were utilized to grow strawberries, peaches, grapes and melons. Protected agriculture was established completely with the use of polythene post World War II. Polythene was first used as a green cover in the year 1948 by Professor Emery Myers Emmert in the US. As per a 1987 estimate, there were more than 30,000 ha of glasshouses in the North-Western Europe alone. Plastic green houses were used in the five continents and major numbers were reported in Japan, China and Mediterranean regions. About 1, 91,500 ha was covered by plastic greenhouses. The estimated use of plastic Greenhouses during 1987-88 is presented in table 1.1. Table 1.1: Estimated utilization of plastic Greenhouse Region Asia and Oceania Americas Middle East and Africa Eastern Europe Western Europe Total

Area in hectares 93000 9000 16000 17000 56500 191500

Source: Jensen and Malter (1995) From 1960s, the concept of greenhouse has improved beyond a devise for plant protection. Even now in the households, some pots are given to protection in green house (Figure 1.2). The concept of a greenhouse is well understood as a system which provides controlled environment agriculture (CEA)with accurate control of root and air temperatures, light, carbon dioxide, plant nutrition, humidity and water. In current scenarios, greenhouses can be considered as vegetable or plant factories. All the aspects of the production system are completely automated creating artificial environment with complete computer assisted monitoring and control.

4

Greenhouse Pest Management

Figure 1.2: Greenhouse hoods with pots. Source: https://www.groworganic.com/greenhouse-6-x-12.html

1.2 INTRODUCTION Greenhouses can be made up of either plastic or glass and they are constructed to grow single or many horticultural crops throughout the year under constant and suitable environmental conditions such as light intensity, relative humidity and temperature which can favor the growth and development of plants. On the other hand, these ideal conditions favor the reproduction and development of mite pests and insects and this permit multiple generations to grow whilst the growing season. Due to enhanced growth of pest populations there will be impact on the greenhouse as a whole. This can be controlled by altering the rate of application of pesticides, biological control and rotating pesticides with diverse modes of action. In general, there will be continuous production and this may lead to higher plant densities and this can control the efficacy of the management strategies involving pests. The low levels of light and low temperatures which generally occur in winter can reduce the activity of several mite pests and insects and this might be restricted to a certain geographic location. The horticultural crops which are grown in

Introduction to Greenhouses

5

greenhouses are well fertilized and irrigated. The ideal conditions which favor the plant growth can also attract several mite pests and insects. So the horticultural plants which are being grown in the greenhouses can supply food for mite pests and insects and this is the main problem faced by producers that they are forced to check their implementation strategies which may decrease plant damage and also crop marketability can be maintained. Horticultural crops which are generally grown in the greenhouses are vegetables, herbs, orchids, woody plant material, tropicals or foliage, perennials and annuals. Many other cultivars, varieties and crops can also be grown in addition to horticultural plants. The horticultural crops grown in the greenhouses are sold to the chain stores, garden centers and to florists. Diverse cultivars, varieties and crops can differ in their susceptibility to certain mite pests and insect and so influencing the amount of pesticides to be used and potential phytotoxicity. Multiple crops which are in different growth stages can make pest management a herculean task. Mite pests and insects can be introduced with the movement of infected plant material from offshore and overseas facility between states or even within the same greenhouse. The movement of infected plant material among greenhouses or within them can help the spreading of mite pests and insect to the healthy crops. Mite pests and insects can be spread within a greenhouse because of the workers, horizontal air-flow or by the movement of infected plant material from one greenhouse to the other. Greenhouses can isolate the mite pest and insect populations from natural enemies such as predators and/or parasitoids which may get entry from the external environment. The cut flowers and vegetable crops which are grown in greenhouse can sustain high levels of mite pest and insect populations and a minor damage to foliage is accepted since flowers and fruits are to be sold. Almost all the ornamental crops are marketed for their high aesthetic value and the foliage and flowers can be purchased by the buyer as a single unit and hence the level of tolerance with mite pest and insect damage is less. The producers administer pesticides regularly whilst the growing season which can put selection pressure on the pests. Both vegetable crops and ornamental crops can be grown in the same greenhouse and this will affect the pest management strategies. The pest management can be hard if there is uninterrupted production of multiple crops. Many crops might be attacked with multiple pests and this could be a severe problem with the producers. Generally, pesticides are to be applied on regular basis. The pest management comprises of about 5% of the total costs linked with the greenhouse operations. If the pesticide is effective for a longer period then the producers will definitely purchase such a product.

Greenhouse Pest Management

6

The producers get their plants from suppliers offshore in South America and Central America which frequently need pesticides such as miticides and insecticides so that the plant quality can be maintained. The mite and insect pests can be engineered to get pesticide resistance on plants that may be used by the recipient producer. The shifting of plant material among different countries can also help in the dispersal of mite and insect pests more specifically winged adults such as leafminers, whiteflies and thrips. With careful examination of the conditions stated above, pest management in the scenario of greenhouses can be considered as challenging task.

1.3 GREENHOUSE EFFECT Generally, the amount of carbon dioxide present in our atmosphere is 345 ppm or 0.0345% (National Oceanic and Atmospheric Administration). Due to excess emission of pollutants into the atmosphere, the proportion of carbon dioxide increases and this leads to the formation of a blanket in the exterior atmosphere. This blanket traps the solar radiation which is reflected from the earth surface. This leads to an increase in atmospheric temperature and this leads to global warming. The ice caps would melt to rise the ocean levels which may lead to submergence of several coastal lines. This process of increase in the average temperature because of the carbon dioxide blanket termed as ‘greenhouse effect’. The covering material for the green house can act in the same way. It is transparent to the short wave radiation and won’t allow the long wave radiation to escape. During day the SW or short wave radiation enters the greenhouse and much of it gets reflected from the ground surface. The radiation which is reflected gets transformed into long wave radiation due to loss of energy and it gets trapped inside the greenhouse. Due to this, there will be an increase in the temperature of the greenhouse. It is appreciable if we consider crop growth in case of cold regions (National Oceanic and Atmospheric Administration).

1.4 ADVANTAGES Some of the advantages of greenhouse while growing plants in controlled environment are the following. • •

They are good for automation of irrigation, environmental controls, application of inputs and artificial intelligence techniques. If crops weren’t grown, the process of drying and relevant operations of the produce which was harvested can use the heat

Introduction to Greenhouses

7

which is entrapped. • The quality of the export can also meet the international standards if even grown in greenhouses. • Various types of growing medium such as compost, rice hulls, vermiculate and peat mass are commonly used in case of intensive agriculture that is possible with greenhouses also. • The horticultural and agricultural crop production schedules can be made accordingly to accrue benefits of the market needs. • The hardening of plantlets generated from the tissue culture technique can be done in a greenhouse. • The germination of seeds is quite high in the greenhouses. • The pests and diseases can be more effectively controlled as the entire growing area will be enclosed. • The gadgets for judicious utilization of plant protection chemicals, seed protecting chemicals, fertilizer and water inputs can be controlled in a greenhouse. • High quality harvest can be produced since the entire process occurs in controlled environment. • The crop productivity can be enhanced. • In any given year, four or five crops can be grown as ideal plant growth conditions exist in a greenhouse. • There will be a chance for self-employment especially for unemployed educated youth. The controlled conditions used in a greenhouse in terms of air, solar radiation and water thus, bestow several advantages (Panwara et al, 2011).

1.5 CLASSIFICATION There are many greenhouse structures which are used for production of crops. Although many advantages do exist for any given greenhouse but there is no ideal greenhouse. Each greenhouse is designed for a specific need. The greenhouses can be classified on the basis of construction and covering materials, utility and shape.

1.5.1 Classification based on Covering Materials The covering materials can be considered as the key component for any greenhouse structure. These materials can influence the greenhouse effect

8

Greenhouse Pest Management

and can change the air temperature inside. The kind of frames and the fixing method also differ based on the covering material used. The type of covering materials used defines the greenhouses into rigid panel, plastic film and glass greenhouses.

1.5.1.1 Rigid Panel The acrylic, polycarbonate rigid panels, fiber glass-reinforced plastic and polyvinyl chloride rigid panels can be used as the covering materials. These panels are common in furrow type frames and Quonset type frames. This material is break resistant and uniform light intensity can be achieved throughout the greenhouse. This is better than the greenhouses made up of plastic and glass. The high grade panels generally have 20 years of span. The important limitation is that these panels are good collectors of dust that impairs the transparency as well as algal growth. Fire hazard can be another important limitation.

Figure 1.3: Greenhouse –Rigid panel. Source: www.cutplasticsheeting.co.uk

1.5.1.2 Plastic film This type of greenhouses is made up of polyvinyl chloride, polyester and polyethylene as covering material. The plastic made greenhouses are popular since they are cheap and the cost incurred while heating the greenhouse is much less than glass. The main limitation is that they last for lesser spans with the best withstanding for four years. Gutter-connected design and Quonset design can be suitable.

Introduction to Greenhouses

9

Figure 1.4: Greenhouse –Plastic film. Source: www.greenhousegrowerstore.com/products/white-greenhouse

1.5.1.3 Glass Glass greenhouses made up of glass were made in 1950. The glass made greenhouses provide higher light intensity. High rate of air infiltration is possible. This can lead to good disease prevention and low interior humidity. Furrow type, ridge type, even span and lean-to type can be employed for building greenhouse.

Figure 1.5: Greenhouse –Glass. Source: www.gothicarchgreenhouses.com

10

Greenhouse Pest Management

1.5.2 Classification based on Construction The type of construction can be affected by the structural material. The span of the greenhouse decides the structural members. If we need to have longer span, then the material should be stronger. Higher number of structural members can be used to build sturdy truss type frames. If we plan for small spans, then we can go for simpler designs such as hoops. Depending on the construction, the greenhouses can be divided into truss framed structures, pipe framed structures and wooden framed structures.

1.5.2.1 Truss framed If the span of the greenhouse is to exceed 15m then truss frames should be employed. Angle iron, tubular steel or flat steel can be welded together so that we can get struts, chords and a truss encompassing rafter. The struts are generally support members which are under compression and chords on other hand also support members under tension. Angle iron purlins generally run along the length of the greenhouse and can be bolted to the truss. The columns can be employed in case of wider truss frames which are about 21.3 meters. Commonly found glass houses are of truss frame type and these are well suited for pre-fabrication.

Figure 1.6: Greenhouse – Truss framed. Source: www.imperialbuilders.com

1.5.2.2 Pipe Framed If we have a clear span of approximately 12m then pipes can be employed

Introduction to Greenhouses

11

in greenhouse construction. The purlins, cross-ties, columns and side posts can be build using pipes. Trusses will not be employed in such a type of greenhouse. The pipe components cannot be interconnected and it is based on the attachment of supporting sash bars.

Figure 1.7: Greenhouse – pipe framed. Source: https://ggs-greenhouse.com

1.5.2.3 Wooden Framed The wooden framed structures can be used for greenhouses if the span is less than 6m. Instead of truss, the columns and side posts can be built using wood. Pine wood can be used as it is cheaper and it provides strength. Timber with machinability, durability and good strength that is available in the local area can be used.

Figure 1.8: Greenhouse – wooden framed. Source: https://ggs-greenhouse.com

12

Greenhouse Pest Management

1.5.3 Classification based on Utility The greenhouses can be divided based on the utilities and functions. If we review various utilities, heating and artificial cooling can be more elaborate and expensive. So the heating and artificial cooling can be important whilst classifying the greenhouses.

1.5.3.1 Active Heating In greenhouses, especially during the night times, there will be lowering of air temperature and in order to protect plants from cold bite, certain amount of heat should be supplied. The amount of heat which is to be supplied depends on the rate of loss of heat to the exterior environment. Many methods are being used to lessen the loss of heat with the help of thermopane glasses, double layer polyethylene and heating systems like solar heating system, radiant heat, central heat, central heat and unit heaters.

1.5.3.2 Active Cooling In summer, it is necessary to lower the temperatures inside the greenhouse for a good crop growth. So we need to make certain modifications so that high volumes of cold air can enter the greenhouse. Such a type of greenhouse has either fog cooling or evaporating cooling pad attached with fan. The greenhouse must be designed so that the roof opening should be 40% and rarely 100% to avoid loss of energy.

1.5.4 Classification based on Shape The greenhouses can be divided based on their style and shape. If we want to classify, then consideration of cross section can be crucial. The longitudinal section is about the same for almost all types and so it cannot be used when we are performing classification process. The cross section gives us the height and width of the structure and the length is almost perpendicular to the cross section plane. The cross section gives us the information regarding the complete shape of the structural members like hoop or truss. Commonly observed types are Quonset, saw tooth, furrow, ridge, and uneven span, even span and lean-to types.

1.5.4.1 Quonset In this type, the pipe trusses or arches are supported with the help of pipe purlins throughout the greenhouse length. Generally, polyethylene can be

Introduction to Greenhouses

13

used as covering material. This type of greenhouses is cheap and can be used when we have less area to cultivate. They are connected as interlocking ridge, free standing style or furrow.

Figure 1.9: Greenhouse – Quonset. Source: http://www.buildmyowngreenhouse.com

1.5.4.2 Saw tooth They are almost the same as the furrow and ridge types and there will be natural ventilation. There will be natural ventilation flow path in this type of greenhouse.

Figure 1.10: Greenhouse – Saw tooth. Source: http://www.cngreenhouses.com

14

Greenhouse Pest Management

1.5.4.3 Ridge and Furrow This type uses two or even more A-frame greenhouses which are connected with other along the eave length. The eave can work as a gutter or furrow so that melted snow or rain can be carried away. The side walls can be avoided in between the greenhouses and this can result in a single large compartment. The interior space can be consolidated and this can lower the labor requirement, reduce the automation costs and lower the fuel consumption since there will be less exposed wall area. This will also enhance personal management. The snow loads should be considered while dealing with frame specifications as the snow by itself cannot slide off from the roofs but there will be melting. Furrow and greenhouses are used in Canada and Europe. In case of hilly terrain, this type of greenhouse can be constructed. The roofs possess unequal width and this can help the structure which can adapt to the slopes of hill. These structures are not of use these days since they have no option to automate.

Figure 1.11: Greenhouse – Ridge and furrow. Source: http://agriculturalinformation4u.com

1.5.4.4 Even Span The roof slopes are of equal width and pitch. This type of design can be employed if we are going for a small size and this can be built on ground level. There are single and multiple span types. The span is around 5 to 9m in case of single span type and the length is 24m with height 4.3m.

Introduction to Greenhouses

15

1.5.4.5 Lean-to This type can be built if a greenhouse is located against an existing building. This type can utilize sunlight and the use of roof supports can be reduced. The roof can be extended with a good covering material and they can be covered properly.

Figure 1.12: Greenhouse – Lean-to. Source: https://www.gardensite.co.uk

Final note: This chapter covered the basics regarding the construction of greenhouses. The various systems used to classify them and their types were covered so that a reader can comprehend the various designs along with their use and application.

CHAPTER 2

IDENTIFICATION OF PESTS

CONTENTS 2.1 Introduction ....................................................................................... 18 2.2 Aphids ............................................................................................... 19 2.3 Broad Mites ....................................................................................... 20 2.4 Caterpillars ........................................................................................ 22 2.5 Cyclamen Mites ................................................................................. 23 2.6 Fungus Gnats ..................................................................................... 24 2.7 Leaf Hoppers ..................................................................................... 25 2.8 Leaf Miners ........................................................................................ 26 2.9 Mealybugs ......................................................................................... 27 2.10 Pillbugs and Sowbugs ...................................................................... 29 2.11 Scales .............................................................................................. 29 2.12 Shore Flies ....................................................................................... 31 2.13 Slugs And Snails .............................................................................. 31 2.14 Twospotted Spider Mite.................................................................... 32 2.15 Western Flower Thrips...................................................................... 33 2.16 Whiteflies ........................................................................................ 35

18

Greenhouse Pest Management

2.1 INTRODUCTION Several types of mite and insect pests can be observed whilst growing crops in the greenhouses. The type of pests differs based on the plant species grown and their geographic location. The mite and insect pests which inhabit these greenhouses are of two main types. They are chewing type and piercing-sucking type. The piercing-sucking insects have specialized mouthparts which allow them to feed on the phloem sieve tubes in order to get free amino acids which are necessary for reproduction and development. If an insect wants good amount of amino acids then it needs to consume higher quantities of fluids present in plants. The plant fluids contain high proportion of other elements other than amino acids. The excess of fluids ingested by the insects will be excreted in the form of honeydew and this is a sticky and clear fluid that can get accumulated on stems and leaves of the plant. If insects have chewing type of mouthparts, they eat plant tissues such as roots, flowers, stems and leaves which result in noticeable damage to the crop plants. The mite and insect pests can be observed on fruit, flower, bud, leaves and even on the growing medium. Mite and insect pests can do damage to plants by feeding on plant tissues. Some of the insect pests can damage indirectly because of the by-products such as honeydew, fecal deposits or frass and molting skins. Some of the symptoms are presented in table 2.1. Table 2.1: Symptoms Type of feeding Internal feeders Epidermal fluid or mesophyll feeders Chlorophyll feeders Miners Chewers Pholem feeders

Pests Cyclamen and broad mites Western flower thrips

Symptoms of damage Nutrient deficiencies, stunted growth and small leaves Silvery leaves, black fecal deposits and sunken tissues Two spotted spider mite Webbing, stippled or bronzed leaves Leafminers Leaf tissue has blotched and serpentine mines Fungus gnat and cater- Leaf yellowing, stunting and pillars larvae wilting. Mealybugs, whiteflies Leaf yellowing, stunting and and Aphids wilting

Whiteflies, aphids and thrips can act as vectors for viruses. The pests which can transmit viruses can be a challenge when we consider pest

Identification of Pests

19

management. Several mite and insect pests consume on various horticultural crops which were grown in greenhouses and the pests can select some plant types which are varieties or cultivars and it may be due to nutritional content or plant chemistry. These factors can affect their distribution in the case of green houses. The primary mite and insect pests of the horticultural crops grown in greenhouses are whiteflies, thrips, shore flies, and mites like cyclamen, broad, twospotted spider, mealybugs, leafminers, fungus gnats and aphids. Some of the minor pests include sowbugs or pill bugs, slugs, snails, scales, leafhoppers and caterpillars.

2.2 APHIDS They have a soft body and measure about 3.1mm in length. They are found in various colors such as pink, brown, orange, black, green and yellow. Color is based on the plant on which they feed. It is crucial to know that they cannot be identified merely with their colors. Several diverse aphid species are known but the most common species are cotton or melon aphid called as Aphis gosypii and green peach aphid called as Myzus persiae. Foxglove or Acyrthosiphon solani aphid and Macrosiphum euphorbiae or potato aphid are some of the species found in addition to commonly available species. Aphids contain tubes at the basal portion of the abdomen and they are known as cornicles. The alarm pheromones will be emitted from these regions in the vicinity of predators namely ladybird beetles. The aphids on the underside of the leaf are shown in figure 2.1. If we observe greenhouses, the aphids which are found are females and they give birth to healthy offspring. They have the capacity to reproduce within 7 to 10 days. The aphids have a peculiar property of parthenogenesis which means they can reproduce without mating. The aphids can reproduce over a 30 day period. Each female aphid can give birth to 100 nymphs with good health. The adult aphids which feed on plants are generally wingless. The winged adults have a capacity to develop in a plant population if the nutritional content of the plant diminishes and if plants have aphid infestations. This condition permits the dispersal of aphids in search of alternative source of food in any given greenhouse. They can grow and reproduce all the year in the case of greenhouses. The aphids generally have piercing and sucking type of mouthparts. This adaptation allows them to eat the phloem sieve tubes and consume the plant fluids. The feeding by aphids can lead to plant stunting, distorted plant growth and yellowing of leaves. Via viruses, these aphids can do indirect

20

Greenhouse Pest Management

damage to plants. In the process of feeding, the aphids secrete a sticky and clear fluid which termed as honeydew. This honeydew can become a substrate for black sooty mold fungi. Black sooty mold has the capacity to cover the leaf surface and can stop plant ability to produce food with the help of photosynthesis. Ants can also consume this honeydew and they can save the aphids from their natural enemies which includes predators and parasitoids. Aphids can manifest as white cast skins post molding. The cast skins can be same as the adults of whitefly and we need to make sure that we use 10x hand lens for observation in order to differentiate the organisms.

Figure 2.1 Aphids. Source: https://www.youtube.com/watch?v=tYIhydi7RAo

2.3 BROAD MITES Broad mite or Polyphagotarsonemus latus are about 0.25mm in length when they become adult. The adults are dark green and sometimes amber in color and they are oval shaped with shine. Four stages are common in their life cycle. They are egg, larva, nymph and adult stages. Females can lay about 40 eggs in their 2-week life span. The longevity can be based on the relative humidity and ambient air temperature. The females that do not mate can produce males only. These virgin female sons can mate with mothers and there will be egg production which yields female offspring. The eggs which are produced will be oval shaped and white in color with protrusions and

Identification of Pests

21

bumps. The eggs produce six-legged larvae and they eventually transform into eight-legged nymphs. The nymphs develop into adults. The broad mite females possess thin and short hind legs. The females are commonly larger than males. The transformation of egg into adult will generally take 5 to 6 days if the optimum temperature is 210C to 260Cwhile it takes around 7 to 10 days if the temperature is 100C to 180C. These mites are dispersed with the help of air currents produced by horizontal air-flow fans in the greenhouse. The leaves of plants nearby which are in contact and the workers who handle the infested plant parts can also contribute in the spread of these mites. The dispersal is more rapid in the event of depleted food or lowered nutritional quality since they try to find plants with good nutritional content. For survival, the broad mites especially females will attach to the antennae and legs of the sweet potato whitefly or Bemisia tabaci and greenhouse whitefly or Trialeurodes vaporariorum. The adults cannot be stationary for longer periods which might favor their attachment. The broad mites cannot attach to aphids or thrips. The male broad mites will have active role in carrying female nymphs to the leaves which are younger and they are involved in transport of female adults and eggs to the new leaves. These mites aggregate as groups while feeding especially under the leaves and also in flowers where the eggs are laid by females. They generally feed on plant cells inside the leaf epidermis with piercing and sucking mouth parts. Their feeding results in shriveled and puckered growth, brittle, curled leaf margins and leaf bronzing. The Broad mites can inject certain toxins whilst the process of feeding. If the population of broad mite is extensive then they migrate and also feed on the upper portion of the leaves which result in distortion of the leaf. Due to its feeding there will be damage to the meristematic tissue of the apical shoot. This will result in reduced growth, leaf area and leaf size and hence the height of the plant will be reduced. The leaves can be dark green and they appear firm. They can also cause malformation and distortion of flowers. This damage will resemble the damage caused by a virus or 2,4 D or deficiency of Boron \or Magnesium.

22

Greenhouse Pest Management

Figure 2.2: Broad mites. Source: http://www.evergreengrowers.com

2.4 CATERPILLARS They are immature or larval stages of moths and butterflies. The caterpillars can produce problem especially during the late spring fall and it is based on the geographic location. The adults generally enter via doors, vents or sidewalls into the greenhouse. The females lay eggs on leaves and they can transform into caterpillars which have chewing type of mouthparts. Several caterpillars can be seen feeding on crops grown in greenhouses. Some of them are tobacco budworm or Helicroverpa virescens , cabbage worm or Artogeia rapae , European corn borer or Ostrinia nubilalis , diamond black moth or Plutella xylostella , corn earworm or Helicoverpa Zea, cabbage looper or Trichoplusia ni and beet armyworm or Spodoptera exigua. Many caterpillars are selective and they feed only on certain plant families. The cabbageworm, diamondback moth and cabbage looper general feed on family Cruciferae or cole crop family. The caterpillars of cabbage looper appear light green and their length is about 38.1 mm. We can observe white stripes along the side of the body. They have 3 pairs of legs close to the head region and extra 3 pairs are present in the abdominal segment, termed as prolegs. The caterpillars of Diamondback moth are light green and long ranging about 12mm and they are capable of chewing and mining leaves of the plant. The caterpillars of cabbageworm are velvety green with yellow stripes along the side of the body and are about 31.2 mm in length. The yellow stripes extend on the back and yellow spots are on each side of the body. The life cycle generally includes egg, larva, pupa and adult. The females which are adult will be active at night and some types

Identification of Pests

23

appear in the day. The females can lay eggs on the lower side of the leaf. The number of eggs depends on the species. Females lay about 100 eggs in their entire lifetime. The eggs can transform into caterpillar which can feed on the leaves. The caterpillars can undergo through series of stages and form instars. There will be increase in the size from one instar to the other. Based on the species, we can observe at least five instars. The caterpillars consume less once they get ready to pupate. This stage can be from 7 to 10 days and it is also based on type of species. The caterpillars transform into pupae stage eventually. Some of the caterpillars can make cocoons and some cannot. These pupae which are formed can be located on the stems, growth medium and also on the leaves. The entire life cycle takes about one month and it is based on ambient air temperature and the plant on which they feed. The caterpillars contain chewing type of mouthparts and they can damage leaves, fruit and flowers. Sometimes they can eat the entire leaf and probably skip the midvein. The presence of fecal deposits on the stem and leaves can signify the caterpillar activity. Some of them can roll leaves and others can simply tunnel into the stems. If the population of caterpillar is not checked then there will be damage to the crops and reduced marketability.

Figure 2.3: Caterpillars. Source: https://www.salisburygreenhouse.com

2.5 CYCLAMEN MITES The cyclamen mite or Phytonemus pallidus is same as broad mite if we study feeding damage, life cycle and biology. The cyclamen mite is transparent, brown, oval shaped and long about 0.25mm. The eggs are generally smooth and there are no protrusions or bumps. The entire life cycle generally takes place about 1 to 3 weeks and it is also based on the ambient air temperature. The females lay about 3 eggs per day and the total amount of eggs in a life span is about 16 eggs. The eggs are arranged in clusters in the terminal buds.

24

Greenhouse Pest Management

This type of mites feeds on plant cells and cause leaf curling, bronzing, leaf twisting and distortion. The feeding results in brittle, rough and wrinkled appearance of the leaf. The plants which are infested will have stunted growth with tiny leaves and they appear silver. The floral buds can abort and may not open at all.

Figure 2.4: Cyclamen mites. Source: http://www.dudutech.com

2.6 FUNGUS GNATS Fungus gnats or Bradysia spp. are generally winged and they measure about 4mm in length. They have long legs and do possess antennae. Their life span is about 10 days. The adults generally get grouped on the surface of the growing medium. The females deposit about 200 eggs into the crevices and cracks of the medium. They transform into legless, white and translucent larvae which is about 6mm long. A clear black head capsule is an important feature to identify the fungus gnat larvae. The entire life cycle constitutes an egg, 4 larval instars followed by pupa and finally adult. The life cycle will get completed in 28 days and it is based on the temperature of the growing medium. The larvae are present on the top 1 to 2 inches of the medium or plant parts like base and crown. The fungus gnat larvae feed on the roots of the plant and this also includes root hairs and upper 2cm of the organic matter present in the medium. The larvae can be spread over the entire profile of the

Identification of Pests

25

growing medium. They are also present in the bottom of the containers close to the drainage holes. These larvae can grow in the medium and can eat the leaves which lie on the medium and in some cases they can tunnel into the crown of the plants. The larvae grow on the moist medium and they also need fungi which can serve as the food to achieve development. The fitness, reproductive capacity and abundance of the adults can be determined by the food type. The larval feeding damages the roots and can stop the water absorption and nutrients. This will result in the stunted growth. The larvae can also cause indirect damage resulting in wounds and they will permit the plant pathogens like Pythium spp. The fungus gnats can be found in the bagged growth medium. Pasteurization of growth medium and treatment with heat may reduce the risk. The larvae can contribute to transmission of fungal diseases such as Botrytis spp, Thielaviopsis basicola, Fusarium spp and Pythium spp. The adults of fungal gnats can also carry spores of soil borne pathogens and foliar pathogens. They include Thielaviopsis basicola, Fusarium oxysporum f.sp. radicus-lycopersici and Botrytis cinerea. The adults can spread spores all over the greenhouse. These larvae can eat propoagules of Pythium, macroconidia of Fusarium. They generally are introduced into healthy plants while feeding. The oospores can pass via digestive tract of the fungus gnat larvae and can be viable even after excretion in the case of Pythium spp.

Figure 2.5: Fungus Gnats. Source: https://www.orkin.com

2.7 LEAF HOPPERS Leafhoppers are of various genera and their size ranges from 3.1 to 4.7 mm in length. They are wedge shaped and slender with a tapered end. They appear as pale green or yellow. The adults and nymphs can move sideways upon the leaves if they get disturbed. Adults are winged whereas the nymphs are not having wings. The females can lay eggs into the stem and leaves.

26

Greenhouse Pest Management

These eggs will transform into nymphs. The nymphs look the same as the adults but they are smaller and absent wings that transform to adults over two weeks. The adults can live for a month and sometimes even longer. The entire life cycle takes around 28 days. The leafhoppers possess piercing and sucking type of mouthparts which are very useful to suck the plant fluids. Based on the species, they feed in the water conducting tissues such as xylem and food conducting tissues such as phloem and some instances both. They destroy cells while feeding and have the capability to inject toxins into plants. This will disrupt the fluid movement via plant parts. Leafhoppers can create stippling on leaves which appears same as damage caused due to Tetranychus urticae or twospotted spider mite. The symptoms generally include necrosis, leaf browning, leaf yellowing, leaf curling and leaf distortion. Molted and white skins can be present in the lower portion of the leaf.

Figure 2.6: Leaf hoppers. Source: https://content.ces.ncsu.edu

2.8 LEAF MINERS Several leaf miner species can be seen in the greenhouses based on the crops grown. Some of the common leafminers are pea leafminer or Liromyza nuidobrensis, serpentine leafminer or Liromyza trifolii and Vegetable leafminer or Liromyza sativae. The fully grown females are 6.3mm long and they appear black and head is yellow. Many of the leafminers have yellow markings all over the body. The females employ an ovipositor which is at the end of the abdomen well into the leaf tissue. This will produce punctures in

Identification of Pests

27

the leaf and they eventually develop into tiny white spots known as stipples over the surface of the leaf. The females generally consume fluids which effuse out from the leaf punctures. A female can lay about 200 eggs in its whole life span. The eggs transform into larvae in about 6 days and they appear brown. The larvae are about 3.1 mm long. The larvae create or tunnel blotched or serpentine mines just under the epidermal layer of leaf. They can affect the quality of aesthetics of greenhouses and there will be economic damages. The damage occurred due to larval feeding can reduce the leaf area which is much needed for photosynthesis. Post feeding inside the plant leaf tissues about 2 weeks every larva makes a hole in the leaf and gets felled out in order to pupate. The adults will get developed from the pupae in about 14 days and gets the strength to a unaffected leaf. Post mating, the females lay eggs into the tissues of leaf. The egg develops into adult in 5 weeks and it is based on the ambient air temperature. There will be several overlapping generations during the entire cropping cycle.

Figure 2.7: Leaf miners. Source: https://wilson.ces.ncsu.edu

2.9 MEALYBUGS Several species of mealybug can be observed in the greenhouse. A major group is citrus mealybug or Planococcus citri. They are segmented with white and are oval shaped. They have waxy protrusions surrounding the body. Females do not have wings and are white in color. They measure 2 to 5 mm when grown fully and on the other hand males are smaller. The

28

Greenhouse Pest Management

life cycle comprises of 5 stages namely egg, 3 crawlers or nymphs and an adult. The males have 6 stages which are 2 pupal stages, prepupa followed by pupa. Before the females die, they produce eggs below body cavity. The eggs are transformed into nymphs, which can move easily searching for food. The nymphs are yellow to orange and later they are white post molts. If crawlers and nymphs successfully locate a feeding place they start the growth stages even before transforming to adults. The males get wings and they can mate with females; post 3 days of which they die. Females will continue to develop and they perish once eggs are laid. The eggs will be shielded below the body cavity of the dead female that hatch. A citrus mealybug can produce 600 eggs. The adult males and nymphs can disperse. Mealybugs have a development period that is extended when compared with mites, whiteflies, thrips and aphids. The entire life cycle takes about 60 days. The entire life cycle is based on the host plant and ambient air temperature. The mealybugs can spread via air or a wind current, improper handling by workers, leaves which touches nymphs, infested plant material and ants. The waxy protrusions generally guards mealybugs from enemies like predators and parasitoids. They will aggregate in more numbers especially at the leaf junctures, stem tips and also leaf sheaths. These are difficult to detect or notice that is associated with challenges in pest management due to identification issues. They cause damage to vascular tissues such as phloem and also mesophyll and sometimes both with the help of piercing and sucking type of mouthparts. The mealybugs are capable of injecting toxins inside plants. The main symptoms are wilting, plant stunting and leaf yellowing. They excrete honeydew which is a clear sticky fluid that serves as a good substrate for the growth of black sooty mold fungi.

Figure 2.8: Mealy bugs. Source: https://www.salisburygreenhouse.com

Identification of Pests

29

2.10 PILLBUGS AND SOWBUGS They are neither insects nor mites. They are mainly classified into crustaceans or isopods. They are convex, oval or oblong in shape. They are generally segmented and appear flat on the lower side. They appear brown, gray or black. They measure about 12.7mm when they are fully grown. They have seven pairs of legs. They are segmented with seven plates which are overlapping and are hardened. They can roll a ball if disturbed and commonly named as ‘roly poly’. The sowbugs lack this capability. The sowbugs have two tiny tails like structures at the end of their body. In the case of pillbugs, appendages are absent. The life span of adults is almost two years or more. Both of them will consume organic matter and other fungi which started decomposing. They possess chewing type of mouthparts. Excess population of sowbugs and pillbugs consume roots and stem of young seedlings.

Figure 2.9: Pill bugs and sow bugs. Source: http://www.pesticide.org

2.11 SCALES The scales share almost similar life cycles as well as same feeding habits. The scales are classified into soft and hard. The female scales measure about 6.3mm. They do not have legs and wings. There are two stages in the life of scales in which they show mobility. The first stage which exhibit mobility is crawler and the other is the male. The eggs which can transform into instars possess legs. This property permits them to migrate onto the plant

30

Greenhouse Pest Management

surfaces like stems and leaves in search of a place for feeding. The late instars and the females cannot move due to loss of legs. The females are legless, wingless and are saclike. The males transform into individuals with one pair of wings and legs. The males have no capacity to feed because they do not have mouthparts. The females of these species have the capability of producing live offspring and some of them lay eggs. The eggs are laid below the female body and are hidden in cottony sacs which generally protrude from the back of the body. The females can lay eggs for 3 months continuously. Soft scales females lay around 1000 eggs. The hard scale females can lay about 100 eggs. The hard and soft scales can be differentiated base on the color and also appearance. The hard scales appear elliptical or circular in shape. The soft scales appear as globular or oval in shape. Both of them have piercing and sucking type of mouthparts. They suck plant fluids from phloem and other tissues. The scales feed on plants and can result in plant stunting, leaf yellowing and plant wilting. The soft scales can produce honeydew and the food canal has good levels of fluid extracted from the sieve tubes of the phloem. The hard scales cannot produce honeydew because the food canal comprise of diverse types of cells and have no capacity to transport plant fluids. The hard sales are capable of ingesting tiny amounts of plant fluids. They can use long stylets to attack large plant tissue areas in order to get the nutrients for reproduction and development. Ants can attract soft scales and hard scales cannot. The soft scales get protection from ants against fungal infection which can utilize honeydew as food. The ants can consume honeydew and they also protect these soft scales from enemies such as predators and parasitoids.

Figure 2.10: Scales. Source: https://mrec.ifas.ufl.edu

Identification of Pests

31

2.12 SHORE FLIES Shore fly or Scatella spp. is on the same lines as houseflies in appearance and measure about 3.1mm. They have black bodies. Every forewing has 5 light colored spots. The legs and antennae are short with small head. The larvae are generally opaque. They appear brown and they do not have black head capsule. They measure about 6.3mm. The shore flies are generally stronger than the adults of fungus gnat. The life cycle comprise of stages namely an egg followed by 3 larval stages, pupa followed by adult stage. The entire life can get completed in 20 days. The development is based on the temperature of the growing medium. These shore flies induce less damage. They can be easily noticed if captured using yellow sticky cards. More numbers of this species can be transported from one greenhouse to another greenhouse via infested plant parts. The crops with adults of shore fly must be rejected. The adults leave black fecal deposits on leaves and hinder the aesthetic quality. The larvae feed on algae and also on the organic matter which is decaying. The larvae are also present in the growing medium. The larvae do not have capacity to feed on roots. They can transmit soil- borne pathogens such as Pythium aphanidermatum and Thielaviopsis basicola.

Figure 2.11: Shore flies. Source: http://cues.cfans.umn.edu

2.13 SLUGS AND SNAILS The slugs and snails are generally not mites or insects and they were systematically placed as mollusks. They are oysters or clams. The snails contain covering which is a hard shell and this protects them from adverse

32

Greenhouse Pest Management

environmental conditions such as sunlight, temperature and also natural enemies. The slugs do not contain hard outer covering. The snails and slugs differ in size: the latter are 1/4 inch to 10 inches (University of Vermont Extension, Department of Plant and Soil Science) .. They can lay eggs in crevices and cracks of the growing medium. The eggs can develop in 10 days based on the temperatures. They develop fully in 3months and rarely does it take about one year. They have radula that works like a tongue which helps to abrade plant tissue and it permits them to feed on leaves and seedlings. They produce ragged-shaped holes in stem and leaves. They are active during night and can hide in the day in the debris, benches and under the containers. They produce a mucus fluid which is silvery and they move on the growing medium.

Figure 2.12: Slugs and snails. Source: https://www.liphatech.com

2.14 TWOSPOTTED SPIDER MITE Twospotted spider mite or Tetranychus urticae measure about 0.4 mm. They are oval shaped and are red-orange or yellow-green. The adults can have markings on both sides of the body. The females are larger than males. The abdomen is pointy and they are elongated. The adult females will survive for 30 days. They can produce about 200 eggs which are spherical in 14 days. The eggs are deposited on the lower side of a leaf. The eggs develop into larvae with six legs and they appear yellow green. They develop into

Identification of Pests

33

nymphs which are having eight legs. They then transform into adults. They are orange red especially during late summer to fall. They enter resting stage or diapauses due to lower temperatures and shorter day lengths. Overwinter they become fertilized females. The transformation of egg to adult typically takes 3 weeks and it is based on the ambient air quality and the plants on which they feed. The life cycle completes in 14 days at 120C, but, a week if maintained at 290C. All the stages in the life cycle can be observed below the leaf surface as the two spotted spider mites are very much sensitive to the ultraviolet light of the sunlight. They have piercing and sucking type of mouthparts. These parts will help them to consume individual plants where they damage chloroplasts, palisade parenchyma and spongy mesophyll. Feeding by two spotted spider mites can decrease the percentage of chlorophyll in the leaves and hence the mechanism of photosynthesis gets impaired. The leaves which are damaged will be stippled and bleached characterized by small yellow and silver gray speckles. Fine molting can also be observed on the upper side of the leaf. The leaves which are heavily infested will appear bronze and eventually turn into brown followed by plant death. If this species is present in excess populations, there will be webbing and premature defoliation. The symptoms can depend on the plants on which they feed.

Figure 2.13: Twospotted spider mice. Source: https://entomology.ca.uky.edu

2.15 WESTERN FLOWER THRIPS The western flower thrips or Frankliniella occidentalis measure about 2 mm.

34

Greenhouse Pest Management

They are slender and long with wings which are hairy. The larvae and adults will appear brown to yellow. The life cycle constitutes an egg followed by 2 larval stages and two pupal stages and eventually develops into an adult. The entire life cycle completes in 3 weeks and it is based on the ambient air temperature typically between 26 and 29 degrees. If optimum temperatures are provided, the life cycle can get completed in 13 days. There is a possibility of new generation in 30 days. The entire development stages are based on the ambient air temperatures. The females can take about 45 days to produce 300 eggs in their life span. The eggs will be inserted into fruits and leaves. The western flower thrips damage plant leaves, flowers and fruits due to feeding. They have piercing and sucking type of mouthparts. They have no capacity to feed on phloem sieve tube. They feed on epidermal and mesophyll cells with the help of single stylet which is present in the mouth. This stylet will help puncture cells. Post insertion of stylet, they insert a pair of them which can lacerate and damage the tissues. The thrips ingest fluids from the plant cells. The symptoms are deformed flowers, sunken tissues in the lower leaf, distorted growth and scarring of leaf. The flowers and leaf produce silvery appearance since the empty cells are filled with air. In the underside of the leaf we can observe the black fecal deposits. The females use sharp ovipositor with which they inject eggs into the tissue and this will create damage to fruits and leaves. The wounds produced due to oviposition and feeding also allows entry of pathogenic organisms such as bacteria and fungi. The western flower thrips can do indirect damage to plants as they serve as vectors for tospovirusessuch as are tomato spotted wilt virus and impatiens necrotic spot virus. The instar larvae get infected with viruses whilst they feed on infected plants and weeds. The adults have the capacity to spread the viruses to the plants which are susceptible. A virus infected plant should be disposed as soon as possible. The damage caused by western flower thrips can produce economic loss for the producers who cultivate via greenhouse. They cannot be suppressed by insecticides especially in the greenhouse because of development of resistance, thigmotactic or cryptic behavior, rapid cell cycle, higher female reproductive capacity, broad host range and small size. By using the benefit of the thigmotactic behavior the western flower thrips protects adults and larvae from insecticides.

Identification of Pests

35

Figure 2.14: Western flower thrips. Source: http://cues.cfans.umn.edu

2.16 WHITEFLIES The species of whiteflies can be seen in the greenhouses and are named as sweet potato whitefly or Bemisis tabaci and greenhouse whitefly or Trialeurodes vaporariorum. The greenhouse whitefly measure about 4.2 mm and the sweet potato whitefly measures about 3.2 mm. Both of them have 4 wings and they are always covered with waxy and white powder. The greenhouse whitefly adults have wings spread flat over the body and this is arranged parallel to the leaf surface. The sweet potato whitefly can have wings at an angle of 450like a roof like arrangement. The females can produce 20 eggs for every 24 hours in the lower sides of the leaves; they laid 300 eggs in their 45 day of life span. The eggs are pale green or purple in case of greenhouse whitefly. The eggs are white or gray with characteristic dark tip in case of sweet potato whitefly. Eggs develop within 10 days and the crawlers or nymphs produced will search for food at the lower side of the leaf. The white nymphs comprise of piercing and sucking type of mouthparts and they are used to suck plant fluids from the sieve tubes of phloem. The nymphs are transparent and flattened and are yellowish-brown. The nymphs cannot move once the feeding site is established and they cannot move for 3 weeks. They transform into pupal stage also called as fourth instar. The greenhouse whitefly pupae are recognized with waxy filaments which enclose periphery side and are elevated with vertical. The pupae will be cake like on the surface of the leaf. The sweet potato whitefly pupae are generally yellowish-brown and are flat in relation to the surface of the leaf.

36

Greenhouse Pest Management

The elongated waxy filaments are absent. The pupae transform into adults in 7 days. The entire life cycle typically takes 4 weeks that is based on ambient air temperature and the target plant which they feed. All the stages of the life are present on the lower side of the leaf. The nymphs and adults feed on the fluids of the plant. The symptoms include plant stunting, leaf distortion, leaf yellowing and wilting. The whiteflies produce honeydew which gets deposited on leaves.

Figure 2.15: White flies. Source: https://www.growveg.co.uk

Final note: This chapter looked at major pests seen in greenhouses. They description along with images can aid a reader to quickly identify the presence of symptoms and take appropriate action to achieve optimum production,

CHAPTER 3

VIRAL DISEASES

CONTENTS 3.1 Introduction ....................................................................................... 38 3.2 Dispersal Mechanisms ....................................................................... 38 3.3 Infection Sources ............................................................................... 39 3.4 Transmission of Viral Diseases ............................................................ 40 3.5 Major Viral Diseases .......................................................................... 41 3.6 Plant Virus Control ............................................................................. 55

38

Greenhouse Pest Management

3.1 INTRODUCTION Viral Infections are a noteworthy issue in case of greenhouse crops particularly in temperate regions. But most endeavors in programs for integrated pest and disease management are centered on fungal and bacterial or fungal disease control and few proposals are given to combat viral diseases. By and large, viral infections are not considered or are dealt with in a simplest way possible. The fundamental explanation behind this is the absence of data about viral diseases to offer suggestions to manage plant viral infection issues. Furthermore, as opposed to bacteria, fungi, pests, no immediate control techniques can be utilized against viral infections. Recently much progress was made in understanding the plant virus and so valuable data was obtained which can help us frame the control strategies. Due to higher costs incurred in mitigating the spread of the viruses through control of vectors, infection source, pest resistance, producers are shifting towards beneficial cultivars which can be appropriate method. The viral management programmes include the integration of measures to reduce the infection sources and virus dispersal. They also involve the reduction of the infections on the crop yields. Knowledge of epidemiology and ecology of viral diseases can give us data required for making certain decisions for the control of viral diseases. The control strategies are dependent on the viral dispersal mechanisms. The control measures can be recommended for viruses with similar manners of dispersal.

3.2 DISPERSAL MECHANISMS The power of viruses to be perpetuated and disseminated in space and time can be based on the methods of dispersal. The knowledge of the dispersal procedures and the methods to control and prevent diseases is important. The virus can be transmitted via biological vectors that are either aerial or soil borne. The aerial vectors can be mites and insects. The insect vectors can have chewing mouthparts like beetles or spa sucking mouthparts like whiteflies, leafhoppers, thrips and aphids. The soil inhabiting vectors can be fungi like Spongospora, Polymyxa and Olphidium or Nematodes like Trichodorus, Longidorus and Xiphinems. The transmission can be by dodder like cuscuta sp. The transmission can be also without involving biological vectors. It can be due to mechanical transmission which comprise of infected plant debris, plant contact and growing practices. It may be via pollen and seed. This can also transmitted via vegetation propagation

Viral Diseases

39

through rootstocks, corns, bulbs, tubers and cuttings. Another method of transmission can be by graft transmission.

3.3 INFECTION SOURCES The plants infected with virus are the sources for spread via biological vector and mechanical schemes and so they must be eliminated as early as possible. The mechanical mode of transmission can be considered as most dangerous type of dispersion method. This is due to the fact that there will be continuous handling whilst intense cropping practices. Some of the viruses are crucial in case of protected crops as the transmission is due to mechanical inoculation whilst cultural operations. If plants are infected by these viruses then it is essential to treat implements in plant handling. The plant debris in greenhouse structures and soil are key sources for infections in susceptible crops. These are subject to removal and there must be disinfection of soil and structures. The material which propagates these viruses which are being employed in planting can be a means for virus introduction at early crop stage. This can provide us a randomized foci pertaining to infection in planting. If more transmission methods are amalgamated then the spread of virus in the plantlets, infected seeds and crop can be important in the epidemic. In some cases, virus-free material which is certified must be used to circumvent virus. About 18% of the plant viruses known are transmitted with the seeds in one or more hosts. The rate of transmission via seeds can differ on the host/viral combination. Viral diseases are dependent on factors such as (Ellouze and Mishra, 2018) • The crop susceptibility • The virulence of the pathogen • The environment • Presence and level of vectors The tolerance levels in case of certification can be based on the type of secondary spread. Minute level of infection can be allowed in lettuce seeds for a good control of lettuce mosaic virus or LMV. In the case of vegetatively propagated plants such as tulip, carnation the source of virus can be infected plants and some of the vegetative derivates like rootstocks, corms, bulbs, tubers and cuttings. Control can be effective if virus-free stocks are used. The certification schemes set to produce virus-free material can be useful. Soil can act as a source for infection. The soil borne viruses can be spread

40

Greenhouse Pest Management

via nematodes and fungi. Some of the viruses such as tobamoviruses do not require biological vector as they are stable present in plant debris which is infected when mixed with soil. The viruses spread can be controlled via disinfection of soil in the case where resistance in cultivars is absent. The virus sensitive crops can be maintained all over the year and this will help us to maintain levels of inoculums and viral infection. The crop rotations must include the non-sensitive species. The management of these hosts can control the viruses.

3.4 TRANSMISSION OF VIRAL DISEASES Several viruses in case of protected plants can be transmitted by invertebrates. The main vectors are sap-sucking insects. Homoptera and aphids are important which can transmit 43% of the virues that are known. The control of virus transmitted through insects can be done by insecticides in order to diminish vector populations. The effectiveness of the control methods is based on the vector/viral transmission relations. The table 3.1 shows crucial properties of various kinds of relations which were dependent on the feeding times required by the vector or acquisition time and inoculation time of the virus, latent period and retention times. The classification provided is dependent on the aphid transmitted viruses. There is no evidence of virus in the salivary system or hemocoel in the case of non circulative transmission. In the case of circulative transmission, the virus can be acquired by consumption. It enters the hemocoel through hindgut. It gets circulated in hemolymph and then it makes its path to salivary gland. The inoculation is by the migration of virus into the salivary duct. The saliva gets introduced into the plant while they feed. The virus gets multiplied in the cells of insects that bestow the title “propagative” on this type of transmission. The insecticide treatment can be not effective in combating virus transmission because of shorter inoculation, latent and acquisition times. The virus can be acquired and then transmitted prior to the vector being affected by insecticides. If we consider protected crops, the chemical treatment can decrease the population of vector and thereby the secondary spread of the disease. In case of non-persistent viruses, tensioactive film products or oils have proved to be effective in combating viral acquisition and followed by inoculation in crops. The insecticidal treatments can be used to regulate inoculation and acquisition times in case of semi persistent viruses. They can regulate latent period, inoculation times and long acquisition times in case of viruses transmitted circulatively. The vector can die even before the

Viral Diseases

41

transmitted virus is active in case of insecticide application. Less number of insects survive such treatments and they may not be effective if viral infections are present. Exhaustive knowledge of disease epidemiology of a region under study can give us crucial information about infection and this will encourage producers to take decisions on taking the call regarding the treatments. It also helps in altering the planting dates to prevent higher vector populations in the plantings. Table 3.1: Classification of virus and vector relations Noncirculative Acquisition time

Circulative

Nonpersistent

Semipersistent

Nonpropagative

Propagative

Seconds

Min.hrs

Min,hrs

Min.hrs

Retention time

Minutes

Hours

Days

Life

Inoculation time

Seconds

Min.hrs

Hrs

Hrs

Latent period

0

0

Hrs.days

Hrs.days

3.5 MAJOR VIRAL DISEASES 3.5.1 Virus Transmitted by Aphids Cucumber Mosaic virus or CMV belongs to genus Cucumovirus. It belongs to family Bromoviridae virions about 29nm sized icosahedral particles and a capsule. It contains single stranded RNA. The RNA molecules are classified into 1, 2 and 3. The first type of RNA has molecular weight of 1.3 X 106, while that of the second type and third type of RNA are1.1 X 106 and 0.8 X 106Da respectively. Some of the isolates of CMV have a minute RNA which can be called as satellite RNA. The satellite RNA has molecular weight of 0.1 X 106Da. It depends on the movement, encapsidation and replication. The RNA satellites have capacity to regulate the symptoms due to CMV. Many varieties of isolates of CMV have been recorded. Based on the serological, molecular, thermosensitivity and symptomatology studies the CMV isolates were divided into two groups. The CMV can be transmitted in a manner which is nonpersistent. It can be transmitted by 60 aphid species or more. This includes Myzus persicase or Sulzer, Macrosiphum euphorbiae and Aphis gossypii or Glover. The rates of transmission can be variable. The transmission mechanisms were explained in 20 species which includes weeds such as Stellaria media Syrill, spinach or bean. The seed transmission was never found in cucurbits. The CMV

42

Greenhouse Pest Management

can be spread mechanically in lab conditions. CMV has large host range which comprise of 1000 species of monocotyledons and dicotyledons. The hosts include passion fruit, Ixora, banana which are semiwoody in nature, Zinnia, Viola, Petunia, Primula, Periwinkle, Lily, Geranium, Delphinium, Dahlia, Aster, Anemone which are ornamental plants, Pea, Spinach, Celery, Carrot, Lettuce, Eggplant, Pepper, Tomato, Watermelon, Zucchini squash, Cucumber, Melon which are vegetable crops. The symptoms differ with the isolate of CMV, environmental conditions, age of plant during infection, cultivars or host species. The plants which are infected with plants can exhibit stunted growth. Leaves will be distorted, mottled and mosaic. Some of the CMV isolates can yield necrosis as well as fruit discoloration and flower abortion can be visible. CMV is distributed all over the world. They are dominant in the temperate areas but their importance is growing in the tropical areas. Many diseases can be caused by CMV and this is also true in case of protected plants like cucurbits, pepper and tomato. Though CMV can be controlled yet a challenge due to its vast host range and its propagation/transmission by aphids. Some of the measures to control CMV incidence in case of protected crops are • Elimination of natural hosts in the vicinity of crops • Usage of seeds which are virus free • Limiting the population of aphids with the help of insecticides • Using aphid proof nets to stop the entrance for aphids • Eliminate the plants which were infected The CMV resistance is available for cucumber especially observed in Chinese and Korean varieties. The sources for tolerance and resistance are observed in cultivated species. In several cases the tolerance and resistance is not possible since CMV species can overcome the resistance provided by plants. The resistance and tolerance towards Aphid vector in the plants can be linked with other control methods. Transgenic squash, cucumber and melon can provide coat protein gene that provides greater level of resistance to many strains of virus.

Viral Diseases

43

Figure 3.1: Cucumber Mosaic Viruses. Source: https://www.gardeningknowhow.com

3.5.1.1 Potyvirus The Potyvirus belongs to the Potyvriridae family and it is considered as the largest of all the plant virus groups (Ellouze and Mishra, 2018). Several members of this family incur economic losses in case of crops which are protected. This can be major disadvantage in terms of production. The virus particles are flexuous and elongated with dimensions of about 680 X 11 nm. One messenger molecule has ss RNA or single stranded RNA whose molecular weight is about 3.5 X 106 daltons. This is attached to a protein covalently. The RNA codes for a polyprotein which is large and it can be cleaved to give viral proteins which are mature. The viral infections are linked with the nuclear and cytoplasmic inclusions, laminated, bundles, pinwheel aggregates. They can be transmitted via aphids in a manner which is persistent. Some of the aphid species like Macrosiphum, Aphis and Myzus are related with huge viral incidences in crops. The transmission via seed is epidemiologically important in case of some potyvirus. This condition can be observed in case of LMV (Lettuce mosaic virus) in lettuce and bean common mosaic virus or BCMV in French bean. This virus can be spread via mechanical inoculation experimentally. Most of the potyviruses have

44

Greenhouse Pest Management

host ranges which are narrow. BCMV can only attack Phaseolus species, PVY or potato virus Y can attack only members of Solanaceae, watermelon mosaic virus 2or WMV2, ZYMV or Zucchini yellow mosaic virus, ZYFV or Zucchini yellow fleck virus can attack only the members of cucurbitaceae and LMV is restricted to Compositae. The Potyviruses can produce various diseases in key crops. The symptoms differ and it is based on host species, plant age, environmental conditions and virus strain. Potyviruses like PRSV-W or papaya ringspot virus-W strain, WMV2 (watermelon mosaic virus 2) and ZYMV (Zucchini yellow mosaic virus )can cause diseases in cucumber, melon, squash, zucchini and water melon. Some of the symptoms are malformed seed, fruit or leaf malformation, mosaic, chlorosis and stunted growth. Reduction in growth, yellow mottling, mosaic and clearning of veins are the symptoms commonly noticed in LMV infections of spinach, endive and lettuce. The potyviruses which attack legumes such as BCMV can result in abnormal seed formation characterized by distorted, discolored and smaller seeds. This genus of Potyvirus can be considered as most damaging as any other plant viruses known. PVY, PRSV-W, WMV-2, ZYMV and BYMV are spread all over the world and they are reasonable for economic problems. Many authors claimed complete loss for water melon, cucumber and squash which are infected with ZYMV. The Potyviruses can also be a great problem even in case of crops grown outside but the protected plants suffer in greater magnitude. The control of the viruses can be achieved by best crop management and integrated control measures. If the virus is transmitted via seed then it is best to used certified seeds which are virus free. This can be basis for effective virus control. Using plants which are virus free can prevent primary infections. Since these viruses are transmitted in a manner which is non persistent, insecticide spraying might not prevent the spread of virus but the control can be done with the help of light mineral oils in the crops which are grown outside. The breeding program is a success if resistance cultivars are developed for the following: lettuce against LMV, Melon against PRSV-W and French bean against BCMV. Transgenic techniques were also attempted to combat these viruses. The cross protection with the help of attenuated ZYMV WK strain has found application to mitigate ZYMV in squash, melon and cucumber.

Viral Diseases

45

Figure 3.2: Potyvirus. Source: https://www.freshfromflorida.com

3.5.1.2 Luteovirus Several yellowing diseases transmitted by aphids can be attributed to members of genus Luteovirus. This can be observed in case of CABYV or cucurbit aphid borne yellows virus and BMYV or beet western yellows. The size of these particles is about 25 to 30 nm. The particles are icosahedral and they have a capsule. They contain single stranded RNA. The transmission is by aphids and they exhibit persistent, non propagative and circulative manners. BMYV can infect tomato, pepper, spinach, carrot, sugarbeet, squash, watermelon, cucumber and lettuce. The symptoms include brittleness and thickening of old leaves, yellowing and chlorotic spotting. CABYV can cause yellowing disease in zucchini squash, cucumber and melon. The symptoms include bright yellowing of leaves, thickening of leaves and chlorotic patches. In cucumber and melon, it is linked to heavy economic losses and this is due to less number of fruits per plant which in turn is due to abortion of flowering. This condition was first described in France in protected and outdoor crops. It was also observed in California, Africa, Asia and Mediterranean area. The management of this disease can be by using integrated measures to lower the aphid population inside the greenhouse. It can be done with the help of nets and chemical spraying. This can control infection foci. Some resistance has been reported in Melon germplasm against CABYV and in Lettuce against BWYV.

46

Greenhouse Pest Management

Figure 3.3: Luteovirus. Source: http://ucanr.edu

3.5.2 Viruses Transmitted via whitefLy 3.5.2.1 Tomato Yellow Leaf Curl Virus (TYLCV) TYLCV belongs to genus geminivirus which belong to plant viruses. The virions exhibit twin isometric morphology. They have single stranded, circular DNA genome that is dependent on the transmission to dicotyledons with the help of Bemisia tabaci or Gennadius which is a whitefly the TYLCV is a member of geminiviruses(subgroup III). Its genome comprise of 6 open reading frames which are in general bidirectionally organized. Two ORFs namely V1 and V2 are in virion sense and Four C1, C2, C3, and C4 are in the complementary sense. They encode proteins which help in encapsidation, transmission, movement and replication of the virus. They are separated by around 300 nucleotides which are also called as intergenic region. This can control the signals for transcription and replication of the viral genome. This virus is transmitted by B. tabaci in a manner which is circulative. They have host range that covers Malva parviflora L., Nicotiana spp., Datura stramonium L., Solanaceae like tomato. TYLCV can infect tomato crops with greater intensity. The symptoms include flower abortion, reduced leaf size, yellowing of leaf margins, curling and stunted growth. They cause serious damage in tomato crops of Central America, subtropical Africa and the Mediterranean basin. The losses can be due to lowered fruit yield. Controlling this virus with the help of crop management to prevent inoculums and vector sources is possible in greenhouses. The use of tolerant

Viral Diseases

47

and resistant cultivars which are commercially available can be used to avoid an attack by this virus.

Figure 3.4: Tomato yellow leaf curl virus diseased (left) and healthy (right). Source: http://www.infonet-biovision.org

3.5.2.2 Clostero Viruses This virus is generally observed in temperate regions. These viruses can be transmitted via whiteflies. This infection can lead to yellowing of plants. Due to the several serious problems attributed, studies in these insects are warranted. These viruses are in general not characterized to the extent as other viruses. But these plant viruses may belong to genus Closterovirus of plant viruses. Some of these viruses are pseudo yellow cirus or BPYV and tomato infectious chlorosis virus or TICV which can be transmitted with the help of Trialeurodes vaporariorum or sestwood and cucumber yellow stunting disorder virus or CYSDV. Others include Lettuce chlorosis virus or LCV and Lettuce infectious yellows virus or LIYV spread by Bemisia argentifolii and B. tabaci. The transmission manner is semipersistent in some cases. The closteroviruses which care transmitted via whitefly can have flexous particles with different lengths based on the species-. The dimensions can be about 900 X 12 nm. The genome constitutes two single stranded RNA. These two RNA are of size 8 kilobases each. This is opposite to citrus tristeza or CTV, beet yellows or BYV which are both closteroviruses transmitted with the help of aphids. Several viruses of this kind were described in the US as they caused large scaled destruction in

48

Greenhouse Pest Management

protected and outdoor crops. Some of the symptoms are necrosis, stunted growth, yellowing of leaves and interveinal yellowing. LIYV generally targets carrot, lettuce, watermelon, squash, melon and sugar beet. 70% of the lettuce crops were damaged. TICV can infect tomato crops grown in greenhouses. LCV can infect lettuce crops but cannot exhibit considerable symptoms in cucurbits. CYSDV is predominant in the Mediterranean area. They are capable to inflict disease in cucurbits. The integrated disease management in case of protected crops is important. Early removal of infected plants and stopping the entry of whiteflies along with the use of insecticides can be helpful for a greenhouse. In Melon, resistance was developed against CYSDV and BPYV.

Figure 3.5: Clostero virus. Source: https://www.ipmimages.org

3.5.3 Viruses Transmitted via Thrips 3.5.3.1 Tomato Spotted Wilt Virus TSMV belongs to the genus Topsovirus and family Bunyaviridae. It has isometric shape. The particles are membrane bound and they have diameter of about 80 nm. They contain Small, Medium and Large linear single stranded RNS strands. One large strand has negative sense. The L RNA or large RNA encodes RNA polymerase. The mRNA codes for NsM protein or non-structural protein and precursor to G1, G2 glycoproteins which are

Viral Diseases

49

related with the lipid membrane. The small RNA encodes nucleocapsid protein and another non-structural protein. This virus is transmitted via thrips like Frankliniella occidentalis or Pergande which is most popular all over the world. The transmission can be propagative and circulative. This virus can be acquired by larvae of the first stage and can be spread by adults and also larvae of the second stage. The adults are of concern epidemiologically as they are mobile and they exhibit virulence through their span of life. TSWV has a vast host range. They infect about 250 species spread over 70 families of both dicots and monocots and cultivated species included. The symptoms include stunted growth, stem malformation, leaf malformation, necrosis, chlorosis, bronzing, mottling, mosaic, line patterns, ring spots, local lesions which are necrotic, chlorotic lesions and in rare cases with no symptoms. The abortion of flowers is visible and there will be fruit malformation, abnormal coloration and necrosis. The symptoms differ and they are based on the environmental conditions, plant age and hostvirus combination. These viruses cause devastating damage in protected and outdoor plants and create more economic losses. Much of the economic losses are observed in ornamental species, as well as vegetables such as lettuce, pepper and tomato. The mitigation of TSWV is quite difficult because of host ranges which are wider of both vectors and viruses. The natural transmission is via thrips. The utilization of insecticides to combat viruses by controlling the natural vectors is useless. The crop management practices are hard to implement. The usage of cultivars which are resistant can be a good solution. The resistance against TSMV is hard since there are problems with identification and characterization that allows their incorporation into cultivars. Much progress has been seen in studies linked with resistance in tomato, lettuce and pepper. The resistance is based on the diversity which is present in TSMV isolates. The production of genetically engineered plants which are resistant to virus is also under progress. For example, ESTs or Expressed Sequence Tags were identified in seeds of peanuts for TMSV (Kudapaa, et al, 2013). Some of the efforts to produce resistant varieties are in progress in protected crops. This can be by using integrated measures so that the viral spread can be limited. Growing of certified vegetal material which is virus free can limit the virus. The thrips can be controlled both chemically and biologically.

50

Greenhouse Pest Management

Figure 3.6: Tomato spotted wilt virus. Source: https://www.apsnet.org

3.5.4 Viruses Transmitted via Bettles 3.5.4.1 Squash Mosaic Virus The Squash Mosaic Virus or SqMV belongs to the genus Comovirus. These virions are almost 30nm and they are composed of isometric particles. They have 2 single stranded RNA segments. They measure about 2.4 X 106 and 1.6 X 106 Daltons. They generate polyproteins and from this structural and non-structural proteins can be produced via proteolysis. The RNA1 can carry information for complete RNA replication and the polymerase is also included. The non-structural proteins can help in movement of protein from cell to cell. This is encoded by RNA2. They also encode polymerase, proteinase, vpg and a NTP binding motif containing protein. Two polypeptides of the coat can be encoded by RNA2. The SqMV can occur as several strains. The isolates were classified into 2 serological groups which vary in their seed transmissibility and in symptomatology and host range. This virus is spread via insects having chewing type of mouth parts like chrysomelid beetles. The infection follows non-persistent manner. It is embryo-borne or seed-borne. The isolates of subgroup 1 are transmitted via seeds to watermelon, melon, squash and pumpkin. The isolates of subgroup 2 are present in squash and pumpkin. The transmission of this virus can be mechanically transmitted via cultural operations and plant contact. The experimental and commercial seed lots can result in 10% of seedlings which are infected. In case of watermelon, about 94% transmission is observed.

Viral Diseases

51

The range of natural host is narrow and it attacks members of cucurbitaceae where many species are susceptible. In experimental conditions, this virus also infects other families. In case of cucurbits, the SqMV can cause infection without any symptoms. They can produce ring spots and systemic mosaic is common. The vein banding and malformation is based on the host and environmental conditions and also based on the strain of the virus. The symptoms present on the fruits can have minute chlorotic areas and greater malformations are observed with dark green areas. Subgroup 1 isolates can cause harmful symptoms in watermelon, pumpkin and melon. The isolates of subgroup 2 cannot infect watermelon but may result in mild symptoms in case of melon and harmful symptoms in for pumpkin. SqMV has been distributed widely in the Western hemisphere. It also occurs in many countries throughout the world and they can be spread via seed lots. The mitigation of this virus can be done by examining these lots so that transmission via seeds can be controlled. If observed the mechanical transmission must be prevented by removing the plants displaying symptoms and decrease the chances via pruning and handling.

Figure 3.7: Squash Mosaic Virus. Source: http://lclane.net

3.5.5 Viruses transmitted via Fungi 3.5.5.1 Melon Necrotic Spot Virus MNSV or Melon Necrotic Spot Virus is a member of genus Carmovirus and

52

Greenhouse Pest Management

it belongs to the family Tombusviridae. The virions measures around 30nm and it is composed of icosahedral particles. It has single stranded RNA which has molecular weight of 1.5 X 106 Daltons. Two proteins are expressed with the help of RNA and another protein gets expressed from 1.9kb subgenomic RNA. The coat protein is generated from 1.6kb subgenomic RNA. MNSV is transmitted via zoospores of the Olpidium bornovanus or Sahtiyanchi which is a fungal vector. The transmission is through seeds. About 405 of the seedlings of muskmelon got infected when cultured in the soil contaminated with Olpidium. The mechanical transmission is also possible during cultural operations. This virus has experimental host range which is narrow. It is restricted to cucurbits. It differs from systemic infections of other hosts. The isolates have failed to infect cucumber and melon plants systemically. The melon isolates can infect melon plants systematically and not cucumber and watermelon. In watermelon, cucumber and melon the MNSV causes minute chlorotic spots in early leaves which can get transformed into minute necrotic lesions which can enhance their size. In watermelon and melon, the necrotic streaks are visible along the petioles and stems. These malformations, necrosis, discoloration of fruits can be observed both internally and externally. MNSV is a pathogen which can affect watermelon, cucumber and melon. Heavy economic losses were observed in Europe, USA and Japan. Grafting on resistant Cucurbita ficifolia rootstocks were used in cucumbers to mitigate MNSV. The melon cultivars against virus are available in the market.

Figure 3.8: Melon Necrotic Spot Virus. Source: https://dpir.nt.gov.au

Viral Diseases

53

3.5.6 Viruses Transmitted via Mechanical Means 3.5.6.1 Tobamovirus The plant viruses of the genus Tobamovirus can cause several diseases which can devastate protected crops. The virions are rod shaped and are rigid. They measure 300 X 18nm and they comprise of single stranded RNA which has molecular weight of 2 X 106 Daltons. Tobacco Mosaic Virus or TMV is one of the members of this genus. The genome constitutes about 5 open reading frames. They encode proteins which have molecular weights of 17.5K, 126K, 183K and 126K respectively. They are responsible for induction of symptoms, movement, encapsidation and replication. Fifth protein has molecular weight of 54K. The fifth protein was observed in vitro but not in in vivo. There is homologous genetic organization and expression of genome in tobamoviruses which was sequenced till now. The tobamoviruses are infectious and the disease agents are persistent in nature. They can be spread and transmitted between plants by contact while cultural operations when contaminated are utilized. The viruses can exist for many years in the plant debris. This can be source of other infections via aerial parts and roots in case there is infection in greenhouse structures. These viruses can be transmitted via seeds. This virus can be transmitted via testa, external seed surface and rarely via the endosperm. The seeds which have infected endosperm can stay infected for years. They are no vectors known. Tobamoviruses can be transmitted via mechanical inoculation. The host ranges is narrow and are restricted to certain hosts. Some of the species can serve as hosts and they belong to various families. Pepper gets infected by pepper mild mottle virus or PMMV, ToMV (tomato mosaic virus) infects pepper and tomato. Cucumber green mottle mosaic virus or CGMMV attacks melon, watermelon and cucumber via vector Lagenaria siceraria. Tobamoviruses can cause various diseases in susceptible species in protected crops during intensive production. So there will be higher density of plants with cultural operations to cause mechanical transmission of virus. PMMV can create faint mosaic in case of pepper leaves. Because of this, there will be malformed fruits and disturbed coloration. They show necrotic areas. ToMV can cause various symptoms and they are based on the environmental conditions, plant age, and cultivar and virus strain type. Mosaics and mottle are present in the leaves and they are malformed. The plants exhibit stunted growth and fruit exhibit mottling and some internal browning is seen. In pepper, the symptoms differ with cultivars. The

54

Greenhouse Pest Management

symptoms are stem necrosis, leaf necrosis, leaf abscission, local necrotic lesions, systemic chlorosis and mosaics. In case of cucurbits, CGMMV can show symptoms such as internal discoloration, distortion, fruit mottling, flower abortion, stunting and symptoms of the leaf include malformation, mottling and mosaic. The Tobamoviruses are the primary problem in case of protected crops. PMMV is most destructive pathogen of pepper crops which are protected. This infection spreads across plants and hence the number of fruits per plant is drastically reduced. ToMV is a virus of economic importance especially in case of tomato crops. The growth of resistant cultivars can decrease the spread of disease. In case of pepper, ToMV can incur damages to susceptible cultivars. The control methods are used to reduce primary inoculums sources. The seeds which are virus free must be used. The seeds can be cleaned by soaking with various solutions. The active ingredients can be sodium hypochlorite, hydrochloric acid and trisodium phosphate or simply by dry heating. Plant debris must be removed and the soil must be heat treated in the greenhouses to prevent primary infections. The secondary spread can be decreased by washing implements and hands with water and soap prior to plant handling. The process of cross protection can be employed in greenhouse tomato crops to mitigate ToMV by tomato seedling inoculation with attenuated strain. This will prevent the infection with disease causing ToMV. The Solanaceous crops can be susceptible and should not be grown nearby. Resistant genes have been incorporated in tomato opposite ToMV. The resistance genes were also incorporated in pepper opposite tobamoviruses such as PaMMV, PMMV, ToMV and TMV; though resistance was found to be overcome by few strains.

Figure 3.9: Tobamoviruses.

Viral Diseases

55

Source: http://seminis.com.au

3.6 PLANT VIRUS CONTROL The greenhouses can be treated as closed systems. The external exchanges are maintained at a minimum. The temporary situation in the simple hermetic structures is on the lines of a Mediterranean region can be considered. The viruses which have devastating effects are soil borne and they are TBSV, ToMV, PMMV, MNSV,LMV, BCMV, MNSV. Some of the viruses which can be transmitted via seeds are LMV, BCMV, MNSV, SqMV, CGMMV, PMMV, ToMV and TMV. There should be adequate knowledge of epidemiology of the disease and dispersal mechanisms. There should be an integrated control strategy. The impact of the infection can be reduced by cross protection and breeding for resistance. The most efficient control method is the development of cultivars which are resistant. The development of transgenic plants and breeding for resistance cannot provide permanent solution against any virus. The virus populations arise variable and have the capacity to mutate with respect to virulence. Cross protection is dependent on the mild strains which can be used to protect against infection by the harmful strain of virus. The mildness of strain is related with target crop and this must be considered if there should be cross protection in greenhouses. Other crops can be sensitive to a virus when grown at a same time. The same technique to prevent dispersal of the mild strain in the crops which are being grown in the vicinity can be employed. To combat virus mutations, the mild strain reversion must be used in the cross protection technique. The risk of co-infection with other viruses which can have synergistic effects must be evaluated thoroughly. This cross protection alone is not good to have a good control of the disease since the protection is based on the homology of the severe strain. It is best to combine various management practices with integrated management strategies of green house. Some of the indirect measures to mitigate virus are prevention of continuous cultivation of species which are sensitive, good plant handling, eliminating virus infected plants, limiting external entrance of insects, disinfection of soil and structures of the greenhouses and usage of dates for planting. The management of such diseases can be done by: (Ellouze and Mishra, 2018) • •

Using seeds that are virus/viroid-free. Hygiene practices (hand/foot washing, avoiding food items)

56

Greenhouse Pest Management

should be adhered to strictly. • Routine checking for mosaic, ringspots, stunting, leaf deformation and irregular flower color or shape. • Insects and weeds ought to be addressed at the earliest. • A thorough clean up after every growth cycle. • Containers or bags from an earlier lot can be avoided due to viruses/viroids in the roots. Final note: This chapter covered various important viral diseases along with details of the viruses. The symptoms were described and the methods to handle the infections have also been covered.

CHAPTER 4

BACTERIAL AND FUNGAL DISEASES

CONTENTS 4.1 Introduction ....................................................................................... 58 4.2 Bacterial Diseases .............................................................................. 58 4.3 Fungal Diseases ................................................................................. 62

58

Greenhouse Pest Management

4. 1 INTRODUCTION Cultivation of crops in greenhouses serves a good option if there is a demand for produce in adverse environmental conditions. Some complex challenges do exist while cropping in greenhouses. Due to intensive cropping systems along with other factors there can be development of bacterial and fungal diseases if efficient control measures are not followed. The losses are too high if proper mitigation measures are not followed.

4.2 BACTERIAL DISEASES Bacterial diseases can damage almost all types of crops grown in greenhouses. Some of them are discussed in this section

4.2.1 Wilts 4.2.1.1 Tomato Bacterial Canker The plants infected exhibit unilateral wilting in shoots, leaves and leaflets. The plants in their early developmental stage exhibit wilting. The vessels present in the sides of the leaves which are wilted show yellowish-brown discoloration. If in some places there is much infection, the cortex can split and cankers which are of several centimeters in length can develop. These plants die eventually in their early ages. The systemic infection of fruit can lead to brown or yellow discoloration of vascular strands. The seeds which are infected can be black or shriveled. The spots which are also called as Bird’s-eye spots can be about 6 mm in diameter and they appear on fruits. This pathogen is a seed-borne organism. It is capable of surviving for many months on the plant debris and cultivation equipment and also in the soil. Large populations can be maintained on tomato leaves. Its infection is around 37 degrees and the optimum temperature will be at 24 to 28 degrees. The symptoms are not visible until they are transplanted. Generally in greenhouses, cultural practices may contaminate the crop.

Bacterial and Fungal Diseases

59

Figure 4.1: Tomato Bacterial Canker. Source: https://www.flickr.com/photos/99758165@N06/35187342650

4.2.1.2 Slow wilt The plants infected with this infection can turn grey-green. There will be stunted growth and no visible wilting is seen. The plants wilt over 6 to 8 months and they eventually die. The pith and vascular tissues at the base of the stem can exhibit yellow discoloration. Root rot and stem cracks can occur. Disinfestations of soil and use of resistant cultivars, grafting and cleaning of propagating material and maintaining hygienic conditions can be good for wilts.

4.2.2 Rots 4.2.2.1 Tomato Soft Rots The plants which were infected with this pathogen exhibit stunted growth. The lower leaves exhibit yellowing at the vein edges and they appear flaccid. The pith transforms from yellow to brown and eventually it get disintegrated. The stem gets hollow and it gets split and they release bacterial slime. The black blotches can be visible along the leaf stalks and stem. A yellowish or light-brown color can be observed in the vascular system. The plants which have stem rot can wilt and eventually die. The plants which get split can survive and may yield in rare cases. The plants which get grown in high relative humidity and which have lush growth can be more susceptible. The infection begins at the leaf scars at the base of the stem and their presence is common even in plants which were never pruned.

60

Greenhouse Pest Management

Figure 4.2: Tomato soft rots. Source: http://www.omafra.gov.on.ca

4.2.2.2 Bacterial Blight These infection exhibit symptoms such as necrosis and rotting and they are systemic diseases commonly found in Saintpaulia, Cyclamen and Chrysanthemum especially in the greenhouses. The pathogen makes their way from the stock plants which were infected and they get disinfected because of cultural practices. The infected plants must be removed and the knives should be disinfected.

Figure 4.3: Bacterial blight. Source: http://www.aganytime.com

Bacterial and Fungal Diseases

61

4.2.3 Leaf and Stem Spots The bacterial speck can result in minute spots which are dark brown and bright yellow halo intact on the tomato leaves. The necrotic tissues cuts off and ragged leaves are seen. The spots may fuse to give brown-black blotches well on the surface of parts. The black spots are about 1mm and they appear on the fruits. The infected leaves can become yellow and they get dried out eventually. The symptoms are almost same as bacterial speck. The spots which appear on fruits are generally raised and they look scabby in nature. These pathogens survive on plant debris outdoors and greenhouse. They are transmitted from one plant to another with the help of water drops. They infect plants via injuries and stomata. The infection need free water available on the surface of the plants.

4.2.3.1 Angular Leaf Spots The damaged plants are mostly melon, zucchini and cucumber with symptoms like minute, angular and leaf spots which are light-grey. They may fuse so that they can cover large area. The infected leaves can appear chlorotic and the areas appear ragged or tear off. Water-soaked spots are visible on the fruit and stem. If there is mush humidity there will be tear drops which form on fruit, stem and leaves.

Figure 4.4: Angular leaf spots. Source: https://www.gardeningknowhow.com

62

Greenhouse Pest Management

The pathogens can survive on the plant debris and can be in seed coat. The bacteria can spread from water through soil and can infect plants. It transmits from one plant to another in cultural practices. Careful disinfestations of soil, hygiene and use of disease free seeds can decrease the incidence of disease. Decreased use of nitrogen fertilizer is crucial for tomato soft rot. The copper fungicides are important chemicals which can be used. Some cultivars are resistant to bacterial spot of tomato and tomato speck, but they are not proved effective in greenhouse systems.

4.3 FUNGAL DISEASES 4.3.1 Root Rots and Damping off The plants in their seed beds can be diseased after or before emergence from the soil. In this case the disease can be called as pot emergence or pre emergence damping off. The seedlings cannot emerge in patches of the seedbeds for post emergence. The plants can rot quickly and can drop down on the soil in pre emergence. The wet soils and low temperatures can diminish and delay the plant growth and hence can favor infection. Several members of fungi can cause damping off. Some of them are Rhizoctonia solani, Fusarium spp. and Pythium spp. which are more common. As the technology improves, the damping off disease is not seen often in case of greenhouses. The crown rots and root rots can be destructive in soil. Some of the diseases which are wide spread are described in the sub sections below:

4.3.1.1 Phytophthora and Pythium Rots Several Phytophthora spp. and Pythium spp. can damage the lower parts of gerbera, poinsettia, carnation, cucumber, pepper and tomato in soilless and soil cultures. In case of tomato crown and root rot may extend to a good height above the level of the soil. The infected area can have dark discoloration while pith is completely destroyed. Phytophthora nicotianae is considered as common pathogen. In case of pepper Phytophthora capsici is quite common. The fruits , stem and collar rot well while leaf spots appear. In case of cucumber, soft rot at the level of the soil can appear after transplanting. The tissues which are infected can shrink and in case of wet weather, there is a possibility of growth of white mycelium. The infected plants wilt and eventually die. Poinsettia which are being grown in pots also get Pythium rot and die. In case of succulent plants due to severe root rot, the death is rapid. In Poinsettia and cucumber Pythium aphanidermatum,

Bacterial and Fungal Diseases

63

Pythium debaryanum and Pythium irregulare are common. The carnations gets infected by Phytophthora and Pythium species which can develop soft rot in the root system and collar and this has common resemblance with Rhizoctonia.

Figure 4.5: Phytophthora and Pythium Rots. Source: http://ipcm.wisc.edu

4.3.1.2 Rhizoctonia Stem Rot This can infect many plants such as poinsettia, carnation and tomato which has symptoms almost the same as Phytophthora and Pythium rots. The Rhizoctonia stem rot is restricted to the collar. The carnation is very susceptible to this infection. The plants which are infected exhibit dry lesions which are pale brown. There can be circular rings at the level of the soil. There will be stunted growth and the leaves appear dull green as well as complete wilting. The pathogen strands may develop on the lesions with stems getting weak to easily break at the site of infection. All Pytophthora , Pythium species and R. Solani species can inhabit soils and they survive for longer periods. The infection occurs at the time of planting and symptoms may appear in case of Pythium and Phytophthora rot. For Rhizoctonia stem rot, the symptoms may appear after some weeks. If moderate soil moisture levels are present the infection can persist. Phyophthora spp. and Pythium spp. can infect soils that saturated with water.

64

Greenhouse Pest Management

Figure 4.6: Rhizoctonia Stem Rot. Source: https://crops.extension.iastate.edu/rhizoctonia-root-rot

4.3.1.3 Corky Root Rot This pathogen mostly damages melon, tomato and eggplant. The leaves of tomato appear dull green as well as stunted growth. The leaves turn bronze and they curl downward. The necrosis of the leaflets will follow. The young roots which were developed are brown in color and are developed poorly. The lesions are scattered and they generally appear on the roots which are large. The roots will become corky and they have variable sizes. There will be fewer yields.

Figure 4.7: Corky Root Rot.

Bacterial and Fungal Diseases

65

Source: https://u.osu.edu

The pathogen can live on the debris of infected root and this is due to the presence of tiny sclerotia. It can be considered as cool weather disease. In case of subtropical countries, the disease can advance during winter with recovery by early spring.

4.3.1.4 Crown and Root Rot As far as plastic greenhouses are concerned, there will be yellowing of lower leaves. It is visible in case of infected plants at the end of the winter which is the time for fruiting. If the infection is intense, the plant wilts and gets chlorotic. A dry lesion of about 10 cm will appear on the collars. There will be a brown discoloration which can be dominant on the root system: quite common in vascular region of the central root, base of the stem and root. Several microconidia are present and they can disseminate the pathogen which can appear on the stem which is infected. The fungus can survive with the help of chlamydospores which can devolop in the soil. This disease gets aggravated by cool weather.

Figure 4.8: Crown and root rot. Source: http://www.missouribotanicalgarden.org

4.3.1.5 Black Root Rot This disease is common in many countries of Europe. It can infect melon and cucumber. It causes brown rot in the root system especially in the cortical tissue. Several sclerotia can get developed and the tissues which are infected appear black. The infected plants can wither and eventually die.

66

Greenhouse Pest Management

The infection can be high if the weather is cold. The pathogen can live for many years with the help of sclerotia. These diseases can be controlled effectively by biological control, grafting on rootstocks which are resistant, using cultivars which are resistant, disinfecting soil, drenching with the help of effective fungicides and use of suppressive substrates which can be natural or artificial in origin.

Figure 4.9: Black Root Rot. Source: https://ohioline.osu.edu

4.3.2 Wilts Many greenhouse crops can get infected either by one or more wilts. In many crops the wilts can cause serious damage and there are several problems in controlling them.

4.3.2.1 Fusarium Wilt The Fusarium wilts can appear on tomato, cucumber, melon, carnation, gladiolus, cyclamen and chrysanthemum in greenhouses. The symptoms include discoloration of vascular bands till the top of the stem, stunted growth, drooping, chlorosis, yellowing and wilt. The presence of large lesions on the stem and wilting of the lateral shoots can be found in infection of Fusarium

Bacterial and Fungal Diseases

67

wilt in melon and carnation. The Fusarium oxysporum has several strains. Each of these cultivars can infect one host and they have a capability of colonizing root system to infect other plants also. They can live in soil for many years with the help of chlamydospores and the inoculums might get diminished over the years. The Fusarium wilt in gladiolus, chrysanthemum, cyclamen, carnation, watermelon and tomato can be aggravated by high temperatures except in melon.

Figure 4.10: Fusarium Wilt. Source: https://www.planetnatural.com

4.3.2.2 Verticllium-Philaphora Wilt This infects several plants and many plants grown in the greenhouses. The disease is more serious in case of family Solanaceae like pepper, eggplant and tomato. Chrysanthemum is more susceptible to this disease. The symptoms are same as the Fusarium wilt. The verticillium wilt can be aggravated due to moderate temperatures. Among them the Verticilllium dahlia is more common. It can live in soil for several years with the help of black resistant microsclerotia. Verticillium albo-atrum can live by producing dormant mycelium which is dark. Almost similar kind of damages is seen with P. cinerescens in carnations in many areas.

68

Greenhouse Pest Management

Figure 4.11: Verticllium-Philaphora Wilt. Source: https://pestid.msu.edu/

4.3.3 Powdery Mildews The powdery mildews can produce more damage to greenhouse crops. Some of the powdery mildew fungi capable of attacking greenhouse plants are E. cichoracearum on gerbera, Microsphaera begonia Sivan on begonia, Sphaerotheca pannosa on roses, Oidium lycopersicum on solanaceous plants, Erysiphe cichoracearum on cucumber and Sphaerotheca fusca on cucurbits. The powdery mildew fungi can attack all the green tissues but L.taurica cannot. There will be white powdery spots which coalesce and can cover large area. Leveillula taurica can infect leaves alone. There will be yellow-green and light yellow spots visible on the upper surface of the leaf and that later get brown. The white mold can be visible on the lower surface rarely. The plants infected with powdery mildew can be distorted and chlorotic. There will be poor growth and premature defoliation in severely affected plants. The infections can be by conidia. If favorable conditions exist, the progress of powdery mildew is rapid. After the season end, these fungi can develop cleistothecia with ascospores especially for E. cichoracearum and S. fuliginea; despite the frequent occurrence, the epidemiological importance is minimum. The conidia can be discharged and spread by wind as well as animal pests. The young conidia can germinate on the plant surfaces which are deprived of nutrients. The relative humidity which helps infection may

Bacterial and Fungal Diseases

69

differ from species and species. Higher relative humidity favors the growth of S. fuliginea by helping the formation of spores and their germination. Excess free water can harm these spores. If the relative humidity is about 99% then there will be good spore germination in case of S. fuliginea and S. pannosa. If the relative humidity drops below 75% then the germination of spores in S. Pannosa is halted. If there is development of mycelium, then sporulation might occur even if the relative humidity drops to 22%. The powdery mildew fungi can develop on weeds and cultivated plants in and outside of the greenhouse production systems. Chemicals like demethylation inhibitors such as fenarimol and triadimefon, pyrimidines like bupirimate and ethirimol, dinocap and pyrazophos can control the powdery mildews in greenhouse systems. The biological control agents were successfully tested against S. pannosa and S. fuliginea. Resistant cultivars of cucumber and melon are available in the market.

Figure 4.12: Powdery Mildews. Source: http://msue.anr.msu.edu

4.3.4 Downy Mildews The downy mildews can affect tomato, cucurbit, lettuce and snapdragon. Phtophthora infestans infect tomato, Bremia lactucae infect lettuce, Peronospora sparsa infect on rose and Pernospora antirrhini can infect snapdragon. These species can have devastative effects on greenhouse grown crops. In case of tomato, the young shoots and leaves are first infected. The infection of the fruits will begin close to the stalk and can spread all over

70

Greenhouse Pest Management

the fruit. The infected fruits and shoots can be brown and firm. In case of cucurbits, the downy mildew can look as circular and angular spots which are yellow on the surface of the mature leaves. The tissues at the spot center die and they appear light brown. The melon and cucumber are very susceptible. In case of lettuce the downy mildews can cause light green and yellow spots on the surface of the leaf. The older spots can turn brown and can get dried. The rose plants when infected can damage their green parts. The leaves of this plant are much susceptible. The leaf infection carries symptoms like being injected with toxins. The leaves which are infected will have dark brown spots which are irregular and they shed readily. The snapdragon plant can be infected with the P. antirrhini. They will have stunted growth and the internodes will become shorter. The leaf borders will curl down and eventually they get dried. After some weeks the plants die. White fungal growth can be seen in moist conditions. The plant infection can occur via mycelium and stomata which can develop intercellular. The conidiphores that are branched are produced and they get inside via stomata. The infection gradually progresses and enlarges towards the periphery of the spot. The conidiospores are hyaline and ovoid with brown color in P.cubensis. They spread due to hygroscopic variations and they spread with the help of water and wind currents. The initial infection can occur due to spores which were transmitted over long distances via wind. Plenty of oospores of P. antirrhini can grow on dead plants. Oospores of the species P.sparsa can infect roses while those of P.infestans and P. cubensis are rare. Phytophthora infestans can live on the tubers of sweet potato and they get transmitted to potato plants post plantations. The inoculums are spread via potatoes to the tomato crops nearby. The downy mildews of the cucurbit can be infectious all the year both in greenhouse and outside. P.sparsa can live in the form of dormant mycelium on the infected stems of rose plants. Peronospora antirrhini can survive as oospores in case of soil and dead plant parts. Freely available water on the surface of plant tissues is crucial for downy mildew fungi to infect. A higher relative humidity favors good sporulation. Peronospora antirrhini can grow well in high relative humidity and low temperatures. The high relative humidity and free water cannot be always a limiting factor for this infection in case of greenhouse systems. The temperature can be more crucial than any other factors. P.cubensis can be grown in case where there is maximum temperature and during those conditions they can infect all year. P.sparsa and P.infestans cannot infect in hotter conditions. The life cycle of the downy mildews encompasses about

Bacterial and Fungal Diseases

71

8 days. If favorable conditions persist there will be many life cycles and the spread is rapid. The chemical fungicides can be of importance in controlling downy mildews. Systemic phenylamides, chlorothalonil and dithiocarbamates can be used in case of greenhouse systems. Some tomato cultivars are resistant to downy mildews. Some of the cucumbers are partially resistant in case of greenhouses. The rose cultivars are much susceptible to downy mildews. If the greenhouses are properly ventilated, then this infection might be controlled.

Figure 4.13: Downy Mildews. Source: https://gpnmag.com

4.3.5 Botrytis Botrytis gladiolorum and Botrytis cinerea can inflict much damage to the crops grown in greenhouses: the latter causes grey mold. They have large range of hosts which includes almost all major crops which are grown in the greenhouses. All the parts of the plants which are in various growth phases can get damaged. Since this pathogen exhibit diversity in damaging plant parts, the symptoms vary according to the host. Water soaked spots appear in fruits, flowers, leaves and young stems. These spots get enlarged if favorable conditions persist. In case of tomato, there will be appearance of circular spots which are green-white and they are also called as ‘ghost spots’. In case of plant parts which are hard like collars and stem B.cinerea can cause cankers and the parts which are present just above them may die. These symptoms are white common in cucumber, pepper and eggplant

72

Greenhouse Pest Management

which are vegetables. The tissues which are infected may die eventually. The grey mold which has conidiophores with spore clusters may get developed upon their surface. In case of tomato, the black sclerotia may develop in the interior stem. Botrytic cinerea can also cause collar rot in lettuce. The plants which are infected can develop necrotic lesions which are brown on the stem, close to the soil and the leaves of the lower plant area. The infection can progress upwards gradually. The plants which were infected can wither and eventually die in a short period. Botrytis tulipae is the cause of tulip fire blight. The spots are visible on the flowers and leaves. There will be bulb rot, blossom blight and lesions on the stem. Botrytis gladiolorum can inflict damage to gladiolus and some of the members of Iridaceae. There will be large spots on the stem and leaves. There will be soft rot, neck rot and pinpoint spots on the flowers. Botyrtis spp. can inflict disease in almost every type of propagating materials. They can be destroyed prior to planting or they may become weak after their emergence. This species can cause heavy post-harvest losses whilst transportation and storage. Bitrytis cinerea can sporulate on every organic material. The spores can be spread with the help of wind or water. The plants which are healthy can be infected via senescent tissues, wounds or through epidermal tissues while they may rarely enter via stomata. The symptoms are not apparent and they appear late once the tissue ages or because of prolonged storage. In case of greenhouse systems the initial infection can be from the outside spores. The inoculums which can get established can be the primary source of infection. If plants are grown in low light intensity, high relative humidity and lower temperatures, then there will be infection due to B.cinerea. This disease can be mitigated by ventilation and constant heating of greenhouses. Fungicides like dicarboxymides and benzimidazoles can be used frequently. If resistant strains are present then it is a good practice to use pesticides or any biocontrol preparations. Latest fungicides can be used in greenhouses but in limited scale. The biocontrol agents like Trichodex has been used in greenhouses.

Bacterial and Fungal Diseases

73

Figure 4.14: Botrytis. Source: https://www.greenhousecanada.com

4.3.6 Sclerotina Rot This is a common disease in pepper, cucumber, tomato, eggplant and lettuce. The infection in case of lettuce starts close to the surface of the soil especially in the water soaked areas. The infection can spread to the roots or can go to the top. The adjoining plants can infect fruits, flowers, leaves and stem. The infected areas can become water soaked. The infection to the stem is more serious. The leaves which are present above the area which is infected can transform into yellow color. They gradually wither and die. In case of wet weather, the white mycelia can develop on the infected areas. This eventually grows into black sclerotia. Sclerotinis sclerotiorum is considered as common pathogen and it can generate sclerotia to a size of a bean and S. minor can generate minute sclerotia. The sclerotia can disperse into soil and they can survive for more years. In favorable conditions, they can produce apothecia which can release ascospores and it may cause new infection. Moderate temperatures should prevail for infection to progress. The control measures are same as grey mold.

74

Greenhouse Pest Management

Figure 4.15: Sclerotina Rot. Source: https://pnwhandbooks.org

4.3.7 Alternaria Some of the diseases spread by Alternaria spp. are described below

4.3.7.1 Tomato Early Blight A collar rot of the plants after or before transplanting can be a primary symptom. In case of well grown plants there will be minute irregular brown spots. They may or may not have concentric rings and yellow halo. They appear on the leaves mainly: with infected leaves appearing ragged and there will be spots and yellow rings appear on the calyx, pentacles, leaf stalks and stem. There will be black or brown spots on the fruits and at the end of the stem there will be leathery surface. If the plants are infected severely then there will be defoliation. Alternaria branch rot and leaf spot of carnation can infect crops especially during mist conditions in the greenhouse. The formation of minute purple spots on the surface of the lead can be considered as primary symptoms. These spots will enlarge and the central part will turn brown. Eventually they turn black because of the development of the spore mass. The infection on the stem appears on the knots. They cause post-harvest rotting in tomato fruits, they can cause leaf spotting in case of cucumber and cankers can be present in case of tomato crops. Alternaria cucumerina can infect squash,

Bacterial and Fungal Diseases

75

melon and cucumber. They do not impose any sort of economic losses in greenhouse production systems. All the species of this genus of Alternaria can exist as facultative parasites to infect weak plants. They can easily live in the plant debris and in the soil. The black spores can also survive on the greenhouse surfaces. Alternaria solani can live on potato that is considered as an alternative host. The spores which can grow on the dead material or in some cases on the host plants can spread with the help of the wind or through splashed water. The plant gets infected via stomata or even through epidermis of leaf. The germination of spores and the infection thereafter requires wide range of temperature. The relative humidity must be greater than 97% for rapid spore germination. The relative humidity can also be at 75%. The tissues which are senescent get infected first. The optimal temperature for A.solani stands at 18 to 25 degrees and for A.cucumerina between 20 to 32 degrees. The temperatures whilst their growing period of the host cannot be factor which may limit their regulation. The control of Alternaria diseases involves iprodione, chlorotholonil and dithiocarbamates. The utilization of healthy propagating material and hygienic measures are crucial if the crops are to be grown in the soil. The inoculums which can survive on soil and frames of the greenhouses must be eliminated as soon as they are identified.

Figure 4.16: Tomato Early Blight. Source: http://www.mofga.org

76

Greenhouse Pest Management

4.3.8 Didymella They are two serious diseases caused by Didymella spp. in the greenhouse production systems. They are stem rot or canker in eggplant and tomato and in case of cucurbits it causes gummy stem blight. These diseases can damage all the aerial parts of the plants in presence of high relative humidity and cool weather. They can infect the root system and collar which can result in yellowing followed by withering. The host plant usually dies because of these complications. The cankers on the petioles and stem are visible. This disease can produce large spots on the surface of the leaves and they may extend to the entire leaf surface. The fruits of tomato can get infected at the end of the stem. The area which is infected can be light brown and it turns pink as there will be lot of pycnidio-spores which can be released. The infected parts can cover about one third of the entire fruit surface. The infection of melon and cucumber fruits by D.bryoniae can occur at the end of the blossoming season. Infection can occur in the interior side of the fruit that cannot be visible from the surface. After the infection many pycnidia can be visible in the infected areas and the color becomes dark brown. The dark perithecia can appear late than pycnidia which are produced by D.bryoniae. The inoculums can be inside the plant residues outside or inside of the greenhouses with an initiation at the collar. These diseases can be spread by culture practices and water splashes. Strict hygienic conditions, plant residue destruction and soil disinfestations can slow the outbreak of these diseases. The fungicides which can be used against other fungal diseases can be effective against these diseases. The lowering of relative humidity and free water on the surface of the leaf can reduce the disease incidence.

Figure 4.17: Didymella. Source: https://en.wikipedia.org

Bacterial and Fungal Diseases

77

4.3.9 Rust The carnation rust can be more severe on the leaves. Some of the other plant parts might also be infected. There will be some minute light green spotsthat get transformed into brown blisters which are powdery as the urediospores devolop. The plant parts which are infected severely can get twisted. They are spread via wind and water splashing and they can get germinated on free water. The pathogen cycle is about 2 weeks. In case of greenhouses, due to wet leaves, the life cycles may be more. The Rose rust is caused by Phragmidium mucronatum. There will be pustules which are yellow orange and they develop underside leaf especially older ones: with more damage in greenhouses. Many species of these fungi can infect rose: mainly autoecious. They are macrocylic fungi and capable of producing telia at the crop season end at the place or uredospores. The infection initiates at spring. The temperature of 27 degrees and free water can be necessary for these uredospores to get germinated. Chrysanthemum Rust is caused by Puccinia tanaceti and white rust of the same plant can be caused by Puccinia horiana. There will be flecks on the leaves which are pale yellow and pustules which are dark brown due to urediospores. The leaves which have more pustules can wither and die. There will be no infection of the stem. It requires moderate temperatures and no necessity for free water for infection to occur. It can survive on the infected leaves and can be spread via wind. The white rust of chrysanthemum has been a destructive disease in the Mediterranean and Europe. There will be cushions which will be white or yellow which can develop underside leaf that become brown. This disease can be favored by moderate temperatures and high relative humidity. Geranium rust and Snapdragon rust can be destructive diseases. Application of fungicides like chlorothalonil and dithiocarbamates can help. Systemic fungicides like oxycarboxin can be used to control rust. The prevention of water condensation can also be effective.

78

Greenhouse Pest Management

Figure 4.18: Rust. Source: http://calag.ucanr.edu

4.3.10 Cladosporium Tomato leaf mold is caused by Fulvia fulva. This can result in yellow or light green spots on the upper leaves. The fungus which is sporulating can appear as olive green and velvety growth with yellow spots on the lower side. This pathogen can live for many months in the greenhouse on the plant debris. It can be spread with the help of water drops and wind. The optimal temperature can be 25 degrees. In case of favourable conditions, the leaf mold can have many life cycles in each season which can destruct crops. There are many strains of this pathogen. Cucurbit scab is caused by Cladosporium cucumerinum that attacks melon, squash and cucumber. It causes angular or circular leaf spots. They look water soaked. The infection on the fruits is much destructive. The water soaked lesions can measure about 1cm long. There are gummy exudations. Corky tissue can grow around the lesions and they finally develop into scabby like tissue. The pathogen can survive on the debris and the spores can be disseminated by air. The relative humidity of 86% and temperature of 25 degrees favors the disease. These diseases can be controlled with greenhouse ventilation. The disinfection of frames and soil of the greenhouses is crucial. Frequent application of benzimidazoles, iprodione and dithiocarbamates can be a good method, some of the cultivars which are resistant can be used.

Bacterial and Fungal Diseases

79

Figure 4.18: Cucurbit scab. Source: https://extension.umaine.edu

Final note: This chapter highlighted significant diseases of bacterial and fungal origin in the context of greenhouses. Along with images and description of symptoms, a reader can grasp the manifestations along with appropriate treatment suggestions.

CHAPTER 5

NEMATODES

CONTENTS 5.1 Introduction ....................................................................................... 82 5.2 Biology of Nematode Pests ................................................................ 82 5.3 Symptoms .......................................................................................... 83 5.4 Monitoring......................................................................................... 83 5.5 Strategies For Control ......................................................................... 85 5.6 Integrated Approach .......................................................................... 88

82

Greenhouse Pest Management

5.1 INTRODUCTION The plant and parasitic nematodes are microscopic in nature and they survive akin to obligate parasites. They are aquatic in nature and they mainly feed on the roots of plant. They can be destructive to food and fiber crops. The loss of yield was pitched in at projected yield loss of 12.3% ($157 billion dollars: Singh et al, 2015). The impact of nematodes is always underestimated as the symptoms of damage are not specific and the damage can be quantified in terms of loss of yield. The nematodes are more harmful to horticultural crops. The root-knot nematodes; Meloidogyne arenaria, Meloidogyne incognita and Meloidogyne javanica are common species that have damaged and reduced the yield to about 60% in case of Mediterranean region. Some of the genera which can damage crops in greenhouses are Heterodera, Paratrichodorus, Trichodorus, Ditylenchus, Paratylenchus, Helicotylenchus, Pratylenchus and Tylenchorhynchus. They affect plant growth in certain environmental niches. In order to control nematode problems it is better to depend on integrated pest management and principles of tolerance, population reduction and prevention. The use of integrated pest management or IPM can stabilize the populations of this pathogen to keep them at acceptable levels. This will result in long-term socio-economic consequences. IPM has been neglected in many parts of the world because there is good availability of soil fumigants which are of broad spectrum type like methyl bromide. This pesticide was proved harmful for stratospheric ozone.

5.2 BIOLOGY OF NEMATODE PESTS The Meloidogyne ssp. are considered as endoparasitic and sedentary nematodes . The second stage is infective and they can freely move and can get penetrated into the area just behind the tip of root. M. javanica, M. arenaria and M. incognita cannot survive below 15 degrees. Once the nematode enters the cortical tissue, it will establish a feeding site. Many root cells in the head region can get enlarged to form giant cells with many nuclei. This can constitute to become a nutrient sink and the nematode gets its nutrients from this site. The juvenile nematodes can get enlarged and may transform into saccate shape whilst their development. Many of the plants which serve as host can respond to Meloidogyne and there will be rapid rate of cell division. We can observe expansion of the cortical regions which are in the vicinity to the point of the infection to yield galls or knots. The female is pear shaped and they can lay eggs into an egg mass which is

Nematodes

83

a gelatinous matrix. This matrix can keep the eggs together at the end of the female body. In favorable conditions, mating may not be necessary for M. javanica, M. arenaria and M. incognita. They reproduce by the process of parthenogenesis. These nematodes can be active all around the year in moist and warm soils that can support growth. The nematode distribution can form a pattern of aggregation in a field. The nematodes can spread in soil and the movement is slow and the dissemination of the nematodes can be by wind, water, containers, machinery, plant material and soil movement. The development of these nematodes can be affected by many factors like soil texture, host plant suitability and temperature. Each nematode need soil temperature of 10 degrees for about 700 days to generate. These nematodes can have broad host range which may include non-cultivated and cultivated plants and also include weeds. The nematodes can survive in sand soils to thus target type of soil.

5.3 SYMPTOMS Some of the symptoms are abnormal wilting, early senescence, yellowing, slow growth and stunting that is based on the wetness of the soil. The symptoms stated above are due to damage in the root system and impairment of the ability to absorb water nutrients and minerals for normal growth. The symptoms are normal if the development of fruit is stressed. If plant growth is uneven we can infer that there should be a nematode attack. It is due to the reason that there will be root invasion and hence greater tissue injury. The plants damaged by nematodes can be positioned in the patches which can reflect aggregation pattern. The appearance of root galls can be considered as an important symptom for root-knot nematode attack. The production of galls is a key response of plant against nematode. The number and size differs and it is based on the susceptibility of the host and the densities of the nematode populations during planting. The root-knot nematode populations are common even if there is no gall formation. The plants with large galls can be scattered in between plants which are unaffected. The plants which are infected can show poor root systems with excess or less number of lateral roots as well as susceptibility to secondary infections by bacteria and fungi which are harmful for plants.

5.4 MONITORING The important use of sampling in integrated pest programs is to link

84

Greenhouse Pest Management

numbers and type of nematodes to enhance the performance of the crop and to evaluate followed by selection of management strategies. Because of the aggregation pattern of nematodes, sample collection with numbers is quite necessary. A sampling tube is used to extract populations that are counted. Some of the things which must be considered are proper handling, efficient storage of sample, soil conditions. Sampling time is reflective of the critical life stages; representative sampling pattern gives data on the population densities and depth of core, diameter and number of cores which are to be needed for soil sampling. The nematodes must be extracted and e identified by trained personnel in well-equipped lab conditions. The identification of these nematode species can be dependent on the morphological features of the juveniles, adult males and females and also on the DNA based techniques like RAPD-PCR and enzyme phenotypes. Investigating roots for the galls caused by root-knot galls is important to know the presence of Meloidogyne spp. in any field. The percentage of gall formation or galling can also give us enough information on the magnitude of damage. The indices pertaining to root galling are dependent on the proportion of galls within the root system. The yield losses and root gall has direct proportionality as they exhibit a linear relationship. For annual crops, the population density at the time of planting can be important to predict the relationships between crop yield and pre-planting populations. These relationships can be utilized in many management strategies which include pre-planting decisions, soil fumigation and varietal selection. Enhanced population densities of nematodes can affect the performance of crop. There can also be minimal density which may not produce loss in the yields. This can be referred to as tolerance limit. The densities of Root-knot nematodes of a juvenile per one cubic centimeter cannot produce measurable yield losses. The densities of nematodes which are greater than 3.5 juveniles per cubic centimeter at planting can produce considerable yield losses of 50% of the crop growth. The stress factors, plant at the infection, plant age, soil type and temperature. Due to immobility of nematodes the concept of emigration and immigration cannot play a key role in the growth of population in a field. The final population at the harvest of the crop can be predicted from the initial population which is before planting. The maximum multiplication rate can be seen in case of lower initial densities whilst unlimited resources are available. If the initial population densities enhances or increases the multiplication rates lowers. When higher densities are present then there will be equilibrium where the initial and final populations are equal. The

Nematodes

85

initial density of the nematodes can get lowered post-harvest if the plants are severely damaged.

5.5 STRATEGIES FOR CONTROL The loss of crops can be prevented by allowing specific nematodes into the soil where they never existed. The regulatory activities such as quarantine, planting media, nematode-free soil and certified material can be employed as exclusion procedures. Good management of populations which were already established should be initiated before planting as there is no procedure to regulate once nematode populations are established. The available strategies for the control of nematodes can be applied simultaneously and the effect must be studied for many seasons as management of nematodes in one crop can affect other crops.

5.5.1 Practices Organic and inorganic media can be used in case of soilless cultivation. Some of the important factors which helps in development and application of soil techniques are water storage, lack of fertile soils, soil salinity and cost of regulating soil borne diseases and pests. These techniques can be applied to ornamentals and protected vegetable crops. These techniques are being used in Mediterranean region as well as Northern Europe. Crop rotation with non-host crops can suppress the build-up of nematodes in annual crops. In rotation sequence, the crop can lower the density of nematodes and this leads to reduced damage in subsequent crop. The crop rotation is good in case of nematode control in case of commercial crops production in greenhouses. It is a best option to use this crop rotation technique as Meloidogyne spp. is polyphagous in nature. This technique can be one of the best strategies in case of subsistence agriculture. Weeds can be reservoirs for infection and they can allow the nematodes to grow. The control of weeds can be crucial in case of rotation technique. The success of this program can be based on the absence of the host roots so that there won’t be feeding and reproduction of nematodes. The weeds can nullify the effect of the non-host and resistant crop plants. Fallowing is a good method which can regulate the population of nematodes by starvation. This method can reduce the population densities of every plant-parasitic nematode. The fallow period can be for few weeks in case of intensive agriculture. If we couple this with root destruction then the short term fallowing can be important and there will be impact on the

86

Greenhouse Pest Management

population densities in the soil. This method has several unfavorable effects on the soil structure and soil organic matter. As there are many root-knot nematode hosts the growth of the weeds must be controlled in the fallow period without which the efficiency is lowered. Repeated tillage can be done to sustain cleaner fallow conditions of the soil. The reproduction of nematode post-harvest can be controlled by the root systems which can be removed mechanically from the soil and they can be exposed to sun and wind. The densities of nematodes can be increasing in case roots are not destroyed. The destruction of crops can help reduce the nematode population. The organic coil amendments can play a crucial role in preventing populations of plant nematodes. They can augment natural enemies as well as stabilize the soil structure and fertility. The soil amendments have been tested with urban wastes, animal wastes, agroindustrial wastes, green manure, plant crop residues and oil cakes. Some of the amendments can be advantageous by improving yields with reduced nematode populations. Exhaustive research is required to characterize the amendments which can then be available in higher quantities for the control of nematodes.

5.5.2 Resistant Cultivars Host plant resistance can be economic, environmentally acceptable and effective method to control nematodes. The plants which are resistant can be cultivated on the infected land without reduction in yield since they remarkably lower the reproduction of nematode. The genetic resistance to this species i.e. Meloidogyne ssp. has been commercially developed in sweet potato, lima bean, cowpea and tomato. The process of genetic engineering can be a good tool to develop new crop cultivars which are resistant to nematodes. Many classes of anti-nematode genes which can encode enzyme inhibitors, enzymes and lectins are being tested for broad spectrum resistance. The antibodies produced by plants or plantibodies have also seen testing for disease and pest resistance. Frequent cultivation of the resistant varieties can increase the development of novel pathotypes which can reproduce cultivars. These pathotypes have been reported in the Mediterranean region. This can occur even if there is no prior exposure to the resistant cultivars. The resistant cultivars can be highly effective if employed in combination with other practices of management. Some of the restrictions while using resistant cultivars must be studied. In case of tomato, there will be a single dominant gene which can be responsible for resistance. If the temperatures are above 30 degrees then the resistance gets weakened. This is the reason

Nematodes

87

why the resistant varieties are only employed in autumn-winter planting.

5.5.3 Resistant Cultivars Organisms that control nematodes that have been studied include bacterial obligate parasites such as Pasteuria penetrans, nematode trapping fungi such as Arthrobotrys oligospora and Verticillium chlamydosporium. Data from microplot and greenhouse experiments have proved that these organisms can lower the density of Meloidogyne spp with Verticillium chlamydosporium showing highest virulence in a 2007 study (Nyongesa et al, 2007). In rare cases, chemical nematicides can yield good results. P.penetrans has been marketed for the improvement of soil in Japan.

5.5.4 Use of Steam Steam can control almost all the soil borne pathogens, insects and weeds. The temperature of the steam must be maintained at 80 to 100 degrees. Post the banning of methyl bromide there were considerable advancements in the greenhouse soil disinfection using steam. Steaming can be considered as more economical and effective than chemical disinfestations. This method cannot be suitable for the greenhouse where there are plastic structures.

5.5.5 Solarization The method of soil solarization is an important method which is also effective. In this technique moistened soil is covered with a clear plastic sheet. This is mainly dominant in the Mediterranean areas. The major use of this technique is that there will be simultaneous regulation of nematodes, weeds, soil borne pathogens and insects. This will also improve the crop performance by altering the physicochemical properties of the soil. The main problem with this technique is that it is based on climatic conditions, as well as the challenges of the cost and the duration of the treatment. An evaluation of the economics, timing and applicability is still required in some of the geographical areas is warranted.

5.5.6 Nematicides They are classified into two groups. They are fumigants and non-fumigants. The fumigant compounds are volatile compounds that are broad-spectrum pesticides. 1,3-dichloropropene can only act as a nematicidal agent. The success of fumigants is based on the moisture content of the soil, temperature,

88

Greenhouse Pest Management

dosage and timing and application method. The fumigants can be applied prior to planting that leads to phytotoxicity. The non-fumigant nematicides are generally non-volatile compounds such as carbamate compounds and organophosphate compounds that are considered as nematostats. They cannot kill nematodes at field concentrations but they can alter the behavior by intercepting hatching, root invasion and movement, feeding behavior, neuromuscular activity and disorientation of males against females. The non-fumigant nematicides can be applied after or before planting. They never gave promising results to control nematodes or any increase in the yield. The use of Oxamyl, fenamiphos and carbofuran showed diminished effectiveness because of the microbial degradation.

5.6 INTEGRATED APPROACH The regulation of Meloidogyne spp. in the case of greenhouses is hard as there will be high soil temperatures which may possibly favor the development of nematodes in the presence of susceptible host. There is a need of correct identification and characterization of the nematode populations which are locally present. The relation between crop performance and number of nematodes and yield must be studied carefully. It is considered as the best practice to use IPM systems to regulate broad-spectrum fumigants. There is a need of fusing one or more strategies which can check nematode problems. This is because of the fact that no single method is effective. The technique of soil solarization can be amalgamated with soil amendments, resistant cultivars and soil fumigants can enhance the efficiency. The resistant plants can lower the reproduction of nematodes remarkably. Some of the epidemiological implications must be considered so that we can be sure about the status of infection for the subsequent crops. The control of nematode populations can be feasible where there will be cold as the low temperatures can slow the development of nematodes and avoid the juveniles of various species from entering the root systems. The cropping systems where there will be no crop in summer seasons can enhance the mortality rate of nematodes as the hosts are absent and the soil temperatures are higher. Final points: This chapter discussed the details of nematode diseases in the context of greenhouses as well as the treatment options. Further research in this aspect is warranted in terms of epidemiological implications as well as targeting juvenile nematodes.

CHAPTER 6

EPIDEMIOLOGY

CONTENTS 6.1 Introduction ....................................................................................... 90 6.2 Disease/Pest Tetrahedron.................................................................... 90 6.3 Epidemics .......................................................................................... 93 6.4 Damage ............................................................................................. 94 6.5 Action Thresholds .............................................................................. 95 6.6 Relationships And Thresholds............................................................. 96 6.7 Research ............................................................................................ 97 6.8 Integrated Control .............................................................................. 98

90

Greenhouse Pest Management

6.1 INTRODUCTION The fields of population biology and epidemiology help us to understand the spread and development of diseases, arthropod pests and some factors that affect the processes. The level of pest infestation and disease is the product of several interacting factors. This level will help us to understand the loss of yield due to pest or pathogen. The research methodologies are almost similar for fungal and bacterial diseases, nematodes, viruses, mites and insects.

6.2 DISEASE/PEST TETRAHEDRON The disease/pest tetrahedron can be used to understand the interaction of pests and diseases with their environment. The tetrahedron (Figure 6.1) consists of 4 important components. These four components can determine the level of pest or disease. The four components are Plant pathogen/pest, host, environment and human activity. The use of chemical control is targeted at influencing the pathogen or pest directly. The integrated control can lower the magnitude of disease or pest by influencing 4 components. A good understanding of various factors on diseases and pests can give us a better understanding of integrated control.

Figure 6.1: Disease/pest tetrahedron. Source: http://ucanr.edu

6.2.1 Pest or Pathogen The infection cycle of a fungal pathogen includes infection phase, sporulation phase, and dissemination phase. The infection phase constitutes spore germination and their penetration of plant tissue followed by colonization.

Epidemiology

91

The sporulation phase constitutes spore production and their maturation. The dissemination phase comprises of liberation, dispersal and deposition of spores. The viral and bacterial pathogens have the same but simple cycle of infection. Some of the pathogens can finish 1 cycle per season while others pathogens can complete many cycles per one season. The amount of disease which develops is a result of cumulative successions of various phases in a given life cycle. All the phases which are observed in the life cycle are subjected to influences from the human activity, host and the environment. The pest organisms belong to different taxonomic groups and their respective life cycles differs accordingly. The dispersal occurs only at adult stage often. The adults search for a habitat which is exploitable. They also search for plants on which they can feed and on which they can oviposit on. If plant is selected which is suitable for ovipositing and feeding the adults will lay eggs which are called as ovipary or they can deposit larvae and nymphs which is termed as vivipary. The progeny can feed and develop on plants on which the oviposition occurs until mature stage is obtained. The adults can feed, oviposit on a selected plant or even migrate to younger plants. Several arthropods can spend whole life cycle on plants. The holometabolous insects can feed on various hosts than the immature fed on. Several greenhouse pests can be multivoltine i.e generate many generations in a year and univoltinism which means one generation per year.

6.2.2 Host The host plant can be a key factor for the disease development than to determine the damage by a pest. This is one of the reason the plant resistance is taken into consideration to regulate disease than to regulate pests. Various cultivars can differ in their susceptibility to certain pests and diseases even if there is no complete resistance. The presence of partial resistance can affect the development of disease by lowering the number of infections by a pathogen. This can be done by enhancing the latency period and lowering the rate of sporulation and lesion expansion or both. This results in development of an epidemic slowly. Various cultivars can affect the host plant selection by a pest, survival and development and so there will be increase in population. Several resistant cultivars are capable to offer resistance throughout their life. Some of the resistance offered is dependent on the physiological age of a plant. The age related resistance can be either young plant or adult plant resistance. Some plant parts can be less or more susceptible to disease because of the age.

92

Greenhouse Pest Management

The physiological state of the plant is affected by nutrition, humidity and temperature. The climatic conditions and nutrient deficiencies can predispose plants to the development of pests and diseases. Unbalanced fertilization can enhance the problems. If there are more nitrogen amendments then the plants will be more susceptible to Botrytis cinerea and there will be an increase in homopteran pets like white flies and aphids. A good understanding of the factors which affects the incidence of pests and disease via the host can help us prevent such outbreaks. Since the host plays a major role in pest population dynamics and disease epidemics, the host plant must be carefully monitored in every epidemiological research. The plant growth, development stage of the plant, nutrition, plant spacing, cultivar and planting date along with an important factor of plant size must be recorded.

6.2.3 Environment Several components of the environment can influence the magnitude of a disease and pest injury via the host plant or the effect may be a direct one on the pest and pathogen. The pathogens are influenced by wind, radiation, relative humidity and temperature. The pathogens are mainly affected by climate conditions at every phase of infection cycle. The spore germination and germ tube growth exhibit optimum temperature curve. In case of several pathogens, the germination occurs at higher level of relative humidity or we can say that excess wetness on the surface of the plant. The expansion of lesions is affected by air temperature. This can also affect the plant tissue temperature. The sporulation is influenced by relative humidity and temperature. The dispersal of spores is affected by air movement and humidity. All these environmental factors will have different effects on the varying crop heights. It is crucial to measure the microclimatic conditions at a height where there is high risk of pest attack. The environment can be manipulated by ventilation regimes, relative humidity, varying temperature and radiation that play a role here.The density of pests can be directly affected by both biotic and abiotic factors other than the host. They are dispersal of pests, fecundity, survival, phenology, air movement, relative humidity, light and temperature. The abiotic factors can also influence the natural enemy populations.

6.2.4 Humans Humans can influence the green house environment and the host plants. A pest or pathogen can be affected by cultural practices such as application

Epidemiology

93

of biological and chemical control types. The cultural practices can make the plants less susceptible or they may also accept diseases and pests. The cultural practice which changes the plant growth like leaf area can affect the microclimatic conditions for pest and pathogens in the crop. In the case of labor intensive greenhouse crops, spread of pests and pathogens all over the crop by the workers is a possibility.

6.3 EPIDEMICS The pest density and the amount of disease which result from the interactions among human influence, plant-pathogen and environment is the main subject of pest population dynamics and plant disease epidemiological studies.

6.3.1 Epidemics of Disease The magnitude of a disease can vary over time. The curve of the magnitude of disease versus time is known as disease progress curve or DPC. It is a sigmoid type of curve. There will be a slow increase at the start followed by a logistic increment followed by a leveling of the maximum level of disease. The disease can be lowered by reducing inoculums at the start. The reduction of the initial inoculums can be main step in the sanitation measures prior to planting. The inoculums can also be lowered during the epidemic by removing affected plant parts. The reduction of inoculums can slow the epidemic that is mainly based on the pathogen type. In the case of powdery mildew fungi, the lowering of initial inoculums can give a small delay of the progression of disease since their spores are presented in abundant in the environment. In case if rare an inoculant is present then sanitary measures can give complete control. The process of sanitation occurs in greenhouses and nurseries. Many of the manipulations of hostplant susceptibility, environment and pathogen are targeted at lowering the rate of the progression of disease. This can be done by pacing down all the processes in the infection cycle.

6.3.2 Population Dynamics The Malthus equation can be applied to study insect demography. This equation which can be used to predict the population is given below as Nt = N0ert Nt denotes the number of pests at certain point of time. N0 denotes the initial time and e denotes the base of the Naperian logarithms. r is the rate of

94

Greenhouse Pest Management

increase of population and t denotes the time elapsed. If we assume r as constant and is independent of conditions which influence the development of pest, reproduction and survival then the growth of population is unlimited. The rate of increase can be called as maximal or intrinsic rate of increase. The maximum population size which any environment resources can sustain can be known as carrying capacity.

6.4 DAMAGE Through the knowledge of pests and the impact of diseases on the yield of crops in case of decision making whilst pest control is necessary. The process of decision-making is dependent on the damage relationship like level of yield loss. The loss of yield can be either loss of quantity or loss of quality or in some cases both. The damage relationships for a particular pestplant interaction can be explained as quantity of yield. This can be expressed as absolute or relative units. The damage relationships can be assessed empirically. These relationships can be analyzed with the help of regression analysis to evaluate yield loss due to infestation. The man limitation is that these models are descriptive and they never take into consideration, the physiological processes which control the yield. The descriptive models can be employed in the integrated control. There are 5 descriptive models which can be used to calculate the magnitude of disease and loss of yield relationship. They are single-point model, Multiple-point models, Integral models, Response surface models and synoptic models. The single-point models are also called as critical-point models. These models are used to estimate the loss of yield by evaluating the amount of disease at any moment. This is generally determined by physiological state of certain crops like onset of flowering. These models rarely are developed linked with time variables. These models were developed primarily for diseases which affect cereals. The use of these models are limited to certain crops which have a yield which gets accumulated over a prolonged period of time or if the harvesting occurs twice or more like greenhouse vegetables. The multiple-point models generally use various disease assessments in order to estimate loss of yield. This model can be used in cases where there is disease progression that is variable based on the environment and host. The integral models generally use the cumulative disease pressure over a certain period of the crop growth. This can be determined by measuring the area under the DPC (disease progress curve) or AUDPC (the area under the DPC). These models fail to demarcate an early moderate epidemic and

Epidemiology

95

severe epidemic under same AUDPC. This limitation can be regulated by adding the weighting factors like number of disease-free days into the model. The Response surface models predict the loss of the yield by employing 2 different variables like crop growth stage and disease severity. The Synoptic models are multivariate models which can estimate the loss of the yield by considering all the independent variables in a single equation. The conceptual framework can be used to estimate the link between the magnitude of the disease and loss of yield which can be applied to damage relationships with arthropod pests. In the case of decision-making, a particular linear function of the yield response to infestation can be assumed. There will be a tolerance level linked with low pest density. The crop tolerance to a particular pest can be high if that pest is capable of injuring leaves of egg plants, cucurbits, pepper and tomato. About 40% of the leaf injury cannot reduce the yield. The sigmoid yield responses to an infestation can be hard to fit but power transformations or logarithmic transformations can linearize the damage relationship. The consideration of disease and pest along with crop variables deliver polynomial relationships which are otherwise hard to interpret and to be employed in decision making process. For a multivoltine condition, the number may differ as per the season. Another approach to determine loss of crop is the use of dynamic simulation models. A model for the development of disease or pest can be combined with crop production and growth. This approach can produce explanatory models. These models can have higher predictive value than descriptive models. The simulation models need a lot of basic information about the physiological processes and their possible effect on the environmental parameters especially on epidemics. It is hard to develop such models compared to models which depend on regression analysis.

6.5 ACTION THRESHOLDS It is important to combine the damage relationships with pest/crop interaction as well as to evaluate the action thresholds and damage. The damage threshold is the maximum level of pest attack and disease below which there is no loss of yield. The action threshold can be a level of pest attack or disease at which the action pertaining to control must be taken to avoid pest or epidemic to attain the damage threshold. The action thresholds for many diseases will be below the logistic increment in DPC. The damage and action thresholds can be considered as key tools in integrated control in

96

Greenhouse Pest Management

case control alternatives are present. The damage threshold is based on the pest/disease level and loss of yield relationship. The action threshold can differ as per the efficacy of the control alternatives and the time it takes to be effective. The action threshold to regulate a pest or disease can be high if a fast acting pesticide is present than the use of biological control in which the natural enemies need certain period to interact. The action thresholds in the case of control of greenhouse whiteflies may be high if we consider several adults per leaf when insecticides are applied. It will be one adult per leaf if Encarsia Formosa is used. The application of action thresholds can reduce the amount of control inputs than general practice. Determining the thresholds cannot be easy. The loss of yield is defined as the weight loss of the product harvested or in terms of loss of economic value. The economic loss can be compared with the cost of the control measures. The conversion of loss of yield to economic yield loss is based on the expected price of the product harvested and it is hard to perform. In case of greenhouse crops, the harvest will be continuous and there will be more complications added with the fluctuating prices in one growing season. The determination of the action thresholds can lead us to some considerations. They are the risk attitude of the grower, effect of control actions on the revenue of the crop and long term consequences of the decisions for pest and disease levels. The use of stochastic models might be useful thresholds for evaluating risks and action model.

6.6 RELATIONSHIPS AND THRESHOLDS Limited information is available pertaining to damage relationships and action thresholds for pests and diseases of the greenhouse. This can be described in pot and flower plant crops for low tolerance to the common pests and diseases. The damage thresholds observed in case of ornamental plants is approximately zero; In case of powdery mildew fungi the damage threshold can be about 5 pustules per square meter. The same pest might have varying damage thresholds if ornamental and vegetable crops are taken into consideration. Tomato can tolerate high infestation caused by leafminer and there will be no loss of yield. If one or 2 mines infest on chrysanthemum, then there will be considerable cosmetic damage. Some thresholds are present for greenhouse pests and vegetable diseases. For cucumber, the model which fits the best to determine damage relationships for powdery mildew is an integral model using AUDPC. The slope of regression line between AUDPC and yield is the same for many cultivars. In this, the disease at an early stage

Epidemiology

97

is compared with the disease at late stages and even severe stages. The yield losses and AUDPC are detected in these situations. Another important challenge to evaluate damage relationships is the ability of some pests to produce many types of damages. This problem can be observed in case of greenhouse whitefly which can feed on phloem sap as well as its ability to damage leaves and fruits and cause photosynthesis to stop by producing honey dew followed by development of sooty molds. The damage threshold can vary and is dependent on what type of damage first occurs and in this case of whitefly, relative humidity plays a major role. In case of humidity, rich greenhouse environments there will be damage by sooty molds and the whitefly densities will be low. About 2500 greenhouse whitefly nymphs per leaf were reported to lower the yield of tomatoes, due to phloem extraction. In another case, it is observed that 60 nymphs per leaf can produce abundant honeydew which may induce a sooty mold on tomatoes when relative humidity is 80% in a span of 8 hours. In case of Bemisia species, another type of damage is present which is linked with their capability to spread Tomato Yellow Leaf Curl Virus or TYLCV. This can enhance complexity to the density of pest and loss of yield relationship. The damage threshold is based on the quantity of virus inoculums which is present in the interiors or near the greenhouse equipment. There is a least possibility of single damage threshold for a given crop or pest. It is based on the climatic conditions and market. The action thresholds are variable especially in IPM programs. In case of natural control, there must be consideration of naturally occurring parasitoids and predators. This can be an additional element to regulate the decision making process.

6.7 RESEARCH A decision must be made for monitoring and sampling purposes. There is a need of accurate assessment of the severity of the disease and pest density. The decisions must be made on the frequency, method and size of the sampling. Apart from monitoring disease or pest it is crucial to monitor the environmental parameters and host plants. The growth of a plant can differ from season to season. The crop yield also varies based on the diseases and pests. The pest infestation and disease can be assessed in terms of number of lesions, insects or pustules. This can be done without monitoring the plant size. In terms of physiology, the amount of plant tissue which is healthy is crucial than the amount of plant infected as the healthy tissues can give us

98

Greenhouse Pest Management

yield. When the loss of yield must be expressed as a yield percentage in the control, a glitch may come up when comparing various the growing seasons or predicting the losses in future. In case of yield in the control differs, the slopes pertaining to explain yield loss percentage can vary from each other: these lines can be forced via origin. In describing the damage relationships the level of lines can be same and can give us accurate explanation of the native situation. The utilization of latest computer programs can help us to execute multiple regression analyses in stepwise. The choice of parameters can be restricted to those entities which can logically be forecasted to play a crucial role in damage relationship so that there will be accurate predictive relationship. Different methods can be employed to simulate various epidemics or densities of the pests. The time of infestation or inoculation can be altered. This can result in varying levels of peat and disease attack at certain point of time. The climatic conditions can also differ that can interfere with sufficient analyses of the impact of yield severity. It is possible to use varying levels of initial density of pests by putting diseased plants on one side of the framework. The level of pest or disease can be altered by differencing environmental parameters. This method is not good as the environmental parameters can influence the yield regardless of pest or disease. A pest or disease is permitted to attain certain level at a time when it stops with a particular pesticide. The experimental design may depend on the model type which is to be developed. For descriptive models which are dependent on the regression analysis, the experiments should be same as the commercial practices. In order to assess yield the plots must be large and it is important to nullify the significant edge-effects. In rare cases, the damage relationships can be produced from a comparison of various greenhouses. In the development of simulation models, the experiments are at a smaller scale and under certain controlled conditions. The effect of more factors on physiology can be determined. So this effect can be quantified and may be incorporated into this model. The prediction of yield can be performed by using the information obtained from the lower level.

6.8 INTEGRATED CONTROL There is a need of thorough knowledge of population biology and plant pathogens of the pests in greenhouse crops that will enable us to develop integrated control measures. The environment and cultural practices can be

Epidemiology

99

altered to avoid epidemics. The producers were interested in the high yields and the greenhouse climate regimes and cultural practices cannot be selected as first factor to avoid pest and disease damage. Due to enhanced awareness of the energy input limits and the chemical pesticides used there was a considerable positive effect pertaining to mitigate pesticide resistance. These issues have helped the producers to adapt to and limit pests and diseases. The integrated control can comprise of amalgamated control measures which may also include chemical control. The chemical control is restricted to an absolute minimum in case of IPM systems. It can be considered as the last line of the defensive barrier. The combination of cultural practices like the choice of cultivars and the climatic control along with the nutrient solution with some other biocontrol measures can give the best perspectives in the coming years. It is based on the greenhouse facilities and crop to evaluate which control measures can be used in the IPM program. In general cases, all the constituents of the tetrahedron can be controlled or modified. Since the control measures will have no negative influence on others, the magnitude of control can be greater if the constituents of the tetrahedron are modified. The use of biological control can be increased with the help of cultural practices that can avoid the explosive disease epidemics and the outbreak of pest or any uneven activity which may enhance the activity of natural enemies. The biological control of powdery mildew fungi can be good in cucumber cultivars which are partially resistant. The control can be the best option in case of greenhouse whitefly which attacks cultivars that are less susceptible to the development of pest. In cased of heated greenhouses, the biological control can be added with climate regime which can encourage the production of biocontrol agents. This amalgamation of biological control and climate control can be a part of IPM. The concept of integrated control is much more complicated when compared with chemical control. This is due to the fact that the tetrahedron components are involved and more research on the interaction is mandatory. Many integrated control programmes have been developed recently. Final note: This chapter explained various systems and programs that are used to model pest-plant associations in a greenhouse. Such models can aid in understanding and predicting epidemics for integrated control programmes.

CHAPTER 7

SAMPLING

CONTENTS 7.1 Introduction ..................................................................................... 102 7.2 Insects ............................................................................................. 102 7.3. Pathogens ....................................................................................... 108

102

Greenhouse Pest Management

7.1 INTRODUCTION The use of Integrated Pest management strategies require exhaustive studies which mainly focus on the precise explanation of population dynamics in time and space so that the assessment of damage thresholds to evaluate key points for control is possible like modeling. It should also focus on the survey to measure the variability in between seasons and also in various regions. The studies must consider a control strategy which can include a survey by the producer of population dynamics. Every area stated above needs certain sampling methods which may vary in their accuracies. Precise measurements, low precise measurements in case of large scale studies and to evaluate variation can be another important step. There is a need for simple but quick methods to be used by producers, that is is another crucial task. The intensity of disease and pest can be quantified with two measurements that are are population size estimation like aphids per one leaf or fungal spores observed in a cubic meter of air and injury quantification of the host plant like the proportion of the leaf tissue infected with larvae. The methods specified must be easier to apply and it should permit rapid estimation. It should also be applied to a wide range of conditions. It must be reproducible and accurate.

7.2 INSECTS 7.2.1 Estimation There are various ways to lower the pest assessment time that it should be examined. The methods can be dependent on the visual abundance indices. The spatial distribution of the pests at every stage is hard to record. The sampling plans require huge data in order to attain a good level of accuracy. Keen attention must be given to measure the pest densities at every sampling point. This can be animportant factor which decides the cost incurred during sampling. The methods can reduce the costs at all times except when automatic counting like picture analysis is used. These methods can also decrease the accuracy that can lead to an error due to sampling itself. It can be used to define the absolute value of the density estimates. Many methods were used to speed up the pest counts via field visual observation which neglects the pest densities per volume or area. Due to this systematic bias and the estimate accuracies, it is important to decide which method we are going to select. An accurate method of getting quantitative data of the pest population is to gather the substrate. The samples must be taken to a lab

Sampling

103

and the samples under study must be isolated followed by counting with the help of a stereoscopic microscope. This method can consume more time and many authors have tried to shorten this time period. The primary step is to extract the samples from the substrate mechanically. They can be extracted by floating and by washing in a high-density medium like saccharose or Berlesse-Tullgren funnels may also be used. When the insects are separated from plant fragments, sand and mud, the clean extract can be subjected to fractionation and sub-samples can be prepared. These steps can yield differing precision and it is based on the surrounding medium on which the insect species survive. The collection of the substrate on which an insect survives might not be good for species like thrips which exhibit mobility. The extraction must be made in the field directly with the help of sweeping nets, vaccum nets or D-vac, mouth vaccum devices and direct picking. The numbers may be counted from part of the total population that can be recovered. This part can be variable and the precision concerning this method can be hard to evaluate. The successive sampling at certain sites repeatedly can allow us to estimate insect density with greater accuracy. The method formulated by Suber and Le Cren was used to know the fish densities in rivers. This method was used by Lapchin and Ingouf-Le Thiec to benthic insect counts. Lapchin has used the same method to estimate the adult and larva; coccinellid densities in case of wheat fields. Boll used the same method for greenhouses cultivating cucumber to measure the number of thrips infested on leaves.

7.2.2 Insects The insect densities can be also estimated in situ without sample collection. The species distribution and their characteristics on the host must be considered and the representative stems or leaves must be observed and they should be highly representative in nature. This method can eliminate the lab stage for estimation of density however, it may not lower the counting time. The observation time can be decreased if there is rough counting. The numbers gathered with this method can be correlated well with the estimated densities of Seber and Le Cren methods. It also permits the development of a sampling plan which is sequential for adult coccinellids in case of wheat fields. The variance observed in insect numbers can be closely linked with the mean of the data. This characteristic implies that the changes in number can be easily noticed by the observers who follow a geometric scale or density rather than an arithmetic scale of density. In such fields, the orders of magnitude can be transformed into plenty classes. It is

104

Greenhouse Pest Management

important to use categorical data that can lower the sampling costs. If we take into consideration the aphid populations, the precise density estimates of Sulzer or Myzus persicae were linked to the proportion of infected leaves in various parts of the potato plants. This method can be used on other plants and has been evaluated by many authors for approval. In 1954, the presenceabsence methods were enriched with a set of plenty or abundant classes. These classes can be purely arbitrary. The sampling units can be divided into poor, medium and heavy infestation classes. Many authors have used precisely defined class as per their localization, size ,and number of colonies. Various kinds of plenty or abundance class systems have been developed as per the insect under study and their environment. There are three main types of classes which can be taken into consideration. There are certain classes which have limits defined by the individual’s i.e. numbers that were observed in one sample unit whilst observation. Leclant and Remaudiere gave logarithmic scale for explaining these limits to measure M. persicae densities on peach. Ferran has used another scale in 1996 to estimate the density of rose aphid on rose bushes. It is dependent on powers of √10 with successive classes like the number of insects seen as 1 to 3, 4 -10 and 11-30 and so on. Boll and Lapchin have used the same scale for Macrosiphum euphorbiae or Thomas in case of tomato greenhouses. Lapchin has evaluated Aphis gossypii on cucumber using this scale. Pure qualitative classes depending on the number and size of the insect patches or the area percentage of the infected shoots can be used. These classes are employed in case of large sampling units like trees. There are some intermediate systems which are dependent on the number of subunits in every class of a qualitative class set. This system was used by Boll for A.gossypii in melon crops and Lapchin used this method to estimate the non-mummified A. gossypii on cucumber. The visual class system should be simple but complete. The usage is based on the number of classes. It is mandatory to have plenty number to explain accurately the variability trends in insect density. It will be difficult to remember if the number of classes used was more. Optimal class number ranges from 5 to 8. The use of visual classes should have a biological basis. A qualitative class which is set should cover various types of the patchiness of the species which might be observed in the field in order to make the class representative. The isolated colonies of A.gossypii on cucumber plants are about few centimeters which can develop around winged insects. After many days of development, the colonies can infect the entire leaf area. These characteristics can be linked with the leaf size which is infested heavily and

Sampling

105

this will decide the classes of abundance. The class system simplicity decides the robustness of the results and the time needed for the observations on the field. The observation of 1 sampling unit can take about 30 sec for each cucumber plant. The class system should cover the range of pest densities/ sampling unit which can be noticed in the observation period in various conditions. The range should be estimated either from the trails or previous knowledge to determine the classes. The results obtained by visual observations can be used without reference to the number of the pests which they represent. The ranked qualitative data can be studied by a large set of statistic tools that are non-parametric. This method may be used to estimate the efficiency of the biological control of the rose aphid on the rose bushes, in case of public gardens. If huge precise data is needed then each visual class should be calculated by computing the variability and mean of the number of the individuals available in the sampling units. This step can be time-consuming as there is a large set of the gathered precise counts. This will be represented accurately and the variability of certain situations in any given class can be selected. The calibration of the classes can be described as a statistical model and they have it as a response variable which is aphid’s density and variable which is termed, visual abundance class. A complex multivariate regression method can be adapted to statistical data. The predictions in these models can be improved by the use of complementary explanatory variables. This type of work along with the calibration with the complementary variables can be performed with 4 class systems and they were used to evaluate the densities of the A.gossypii and Lysiphlebus testaceipes which is a parasitoid on cucumber in case of greenhouses. There two visual systems which were used in the estimation of densities. Detailed visual method for any leaf and there is another method called as quick visual method or QVM. There were constructed as per the apparent numbers of the individuals whilst observing the units in the process of sampling. The QVM can be employed for healthy aphids. The resultant 4 classes were dependent on the proportion of the leaf area which is infested and also on the size of the leaf. The precise counts were made on the sampling units and they can be used in the form of response variable. The data were classified into validation and reference sets. The reference sets can be used to produce the regression models. The validation sets can be used to test the robustness. The complementary explanatory variables which are to be selected is important for the development of the regression models. These variables can be selected for influence on the goodness of fit in case of models and

106

Greenhouse Pest Management

the required collecting time. If we use the detailed visual method along with the target population of the model was either mummified and healthy aphids then there will be 7 explanatory variables which can be used. They are the number of leaves infected by the aphids on the host, the number of leaves on the host plant, the vertical rank of the plant leaf, and the 2 visual classes of the target population on the lower and upper neighboring leaves on the host, visual class of the non-target population on the leaf and visual class of the leaf. This data can be easily collected whilst sampling and without any higher costs. The QVM sampling of the plants can result in a mean error of about one class/plant. The DVM may carry a mean error of much less than 1 class. The range of residuals can be the same for both validation data sets and reference data sets and hence there will be robustness in these models. This method has been employed now to calibrate visual class systems for various pest species on the crops of the greenhouses mainly vegetables. They may comprise of aphids on sprout, eggplant, melon, tomato and thrips on cucumber. If a new regression model is to be tested there must be certain attention to the sampling and development of validation data sets. They should include similar combinations of the variables which can be used in field sampling.

7.2.3 Reduced Sampling Time Reducing the time required for estimating the insect densities in the sampling units can carry certain cost which can decrease the precision. The time which is saved permits the observer to enhance the number of units which are to be taken into account in any sampling plan. So there will be some precision of the variance and mean estimates of the density. The time which was saved can be enhanced if visual methods were employed. Mechanical methods like washing can be slower. The evaluation of the precision in case of visual methods needs a calibration process which is time-consuming. This must be repeated in every study and this may deal with various species, varying scale of observation and environments of the insects. The decision to take this work will be based on the chance of constructing a better visual system. The four criteria of evaluation can be described effectively. The boundaries can be stable in space and time. The visual classes can be distinct but simple. The boundaries must be easily identified in the field. All the insects should be visible. These methods cannot be employed for aphids present in the rolled leaves. The insect density should be highly variable. The benefit of constructing these calibrated visual scales can be based on

Sampling

107

the species which are observed and the environment which supports them. The scales can be employed for almost all aphid species as they attain high densities. They might have strong aggregated distribution patterns. The sampling units may not be destroyed. The crops can be monitored easily and the population dynamics can be researched separately in various fields. These methods allow large scale surveys. A regular sampling grid can be employed in each greenhouse and it may need less than an hour of observation at a time by 2 people on each occasion of sampling.

7.2.4 Monitoring All the phytophagous insects can be highly aggregative. The number of units which are required in a sampling plan which may be reliable of the density estimates can be increased. This is a serious problem at the initial stages of crop season when the insects get clumped with immigrants and for species with higher increase rate. This is common in most of the greenhouses. The efficiency of biological control can be based on the identification of initial foci. Many early trails were performed in tomato greenhouses which may develop sampling schemes. They may be compatible with the time constraints of the producer. Eggenkamp-Rotteveel Mansveld employed stratified random sampling. The absolute count was performed on just 0.6% of the total plant species which were spread evenly all over the greenhouse. The data obtained were compared with absolute counts which were obtained from 18000 plants grown in the greenhouse. The results produced showed that random sampling cannot reflect the accurate numbers and the whitefly distribution. The absolute counts might not be useful. The same conclusions were obtained by Ekbom in 1980. These studies showed that there is a need of a special device to detect whiteflies in the early stages. This was also attempted by Guldemont and den Belder in greenhouses where chrysanthemum is grown. They used incidence counts and yellow sticky tapes at the same time in order to investigate the moment and the level of pest attacks on the major crops. The pests are mainly caterpillars, spider mites, whiteflies, aphids, thrips ,and leafminers. After several experiments, it has been proved that the traps can be used for monitoring the number of thrips and leafminers in the entire season and especially for aphids it is winter season. Less emphasis must be laid on the usage of traps than on crop sampling. The minimal density of pests and distribution can demand the fixed sampling sites not suitable. Diverse approaches for sampling aphids have been investigated. The main problem with these experiments is that they were done in the open field

108

Greenhouse Pest Management

cereal crops but not in the greenhouses. The spatial heterogeneity existing in the population may be incorporated in the sequential sampling plans. They are based on the relationships of the mean of density and variance. The sample size can be selected as per the reliability needed. Incidence counts were replaced by précis counts. The incidence counts can enhance the sampling efficiency of aphids. There must be a firm relationship between the precise counts and incidence counts at the scale pertaining to sampling unit. The loss of precision in each unit can be compensated by enhancing the number of units in a specified period of time. It is a good practice to fuse errors which were induced due to the representation of the sampling scheme and by incidence counts. This was done in case of aphid predators in cereals. The monitoring of insects in the greenhouses can be a complicated problem. The least expensive and most accurate methods must be developed in every situation and then they must be altered to produce required precision for a biological question.

7.3. PATHOGENS The intensity of diseases can be estimated with the help of 2 distinctive measurements. They are disease incidence and disease severity. The disease incidence is the number of units infected which can be expressed in the form of a proportion of all the number of units assessed like the percentage of infected twigs, tubers, fruits, leaves and plants. This can be a quintal measurement. The disease severity can express the intensity of the symptoms like the area of affected plant tissue by disease and it can be expressed as a proportion of a number of lesions per plant unit and the total leaf area. The measurement of disease intensity in any crop is basic to integrated pest management. The disease incidence can be easier to access with good accuracy. The accuracy estimates pertaining to the severity of diseases can be hard to obtain. A producer can readily overestimate severity in less time. For decision-making the disease incidence must be a preferred measurement and not disease severity. The disease severity on the other hand, can correlate with the crop loss and yield. Since the incidence values are accurate several attempts were made to link or correlate incidence with severity. In the case of low disease levels, there will be a good correlation between incidence and severity. In the case of higher levels of disease, the relationship between the severity and incidence may become scarce. If there is a significant correlation, the similarities between 2 measurements can be confirmed. More easily the incidence values measured may be used in the

Sampling

109

assessment of a disease. If the relationship is not linear then there will be a need for appropriate transformation. Generally a square root transformation of the severity values can be used to produce the regression equations which may predict the severity. Several schemes which warn opposite diseases and pests are based on the enumeration but not estimation procedures. The visual estimation of disease severity can be employed for estimating certain disease severity in a particular field. The methods which are for visual assessment of any disease can be classified into 2 categories. The first is that they contain descriptive keys which may utilize arbitrary scales, percentages, grades, ratings, and indices to quantify a disease. These keys were used to estimate the severity of hosts with varying disease resistance and hosts which were exposed to different cultivation procedures and environmental conditions. The disease can be described by 1 to 5 categories with 1 being none and 5 being extreme. The severity can be denoted by ranges from none to heavy. It is a good practice to average values since individual category values are of no use. The second category involves the application of standard area diagrams. The pictorial representations of the host with the graded amount of disease can be related to the infected leaves to permit the estimation of the severity. The estimates of the severity can be proportional to the absolute leaf area which is infected. They cannot be expressed as an arbitrary maximum severity value. The standard area diagrams permit the estimation of the intermediate disease levels by comparing a plant which is diseased with that of less or more disease. Horfall and Barratt in 1945 showed the eye limitation in assessing a plant disease. The law framed by Weber-Feckner states that the visual acuity can be proportional to the log of the intensity of the stimulus. It was further noticed that the visually estimating disease severity can be observed but with 50% assessment of injury to the diseased leaves and 50%of the injury to the healthier leaves. They developed a disease rating scale. This scale comprised of 12 equal divisions of severity on a log scale with 50% median value. The division of this scale constitutes decreasing ranges of the severity when decreasing or increasing from 50% severity. The scale and standard diagrams produced can result in a logarithmic decrease in the visual acuity in severity estimation which approaches to 50% with the help of representative keys. The estimations of the severity intermediate among the 2 keys can be made with systematic interpolation. The visual estimation of severity can vary significantly from the accurate amount of the disease. If an observer is unaware of the limitation existing in visual acuity at the midrange of

110

Greenhouse Pest Management

the severity, then the estimated severity and actual severity can be linearly related. The variance of the estimates can be free from the severity. The Weber-Feckner law shows that the real true confidence intervals of the estimates produced of severity can approach the linear relationship at high and low levels of the disease. This can go beyond this line with enhancing severity with a max variance at about 50% of the disease. The Inter-rate reliability can be defined as the ratio of the true variance with the total variance. This comprises of the variance component for the error in the raters. The improved sampling designs and large sample size can reduce the actual and total variance. The limited resources always restrict the sample size. If more raters are involved then it is hard to quantify the bias due to any single individual. Shokes in 1987 tried to measure the intrarater repeatability with the test-retest correlation process. The correlation coefficient or r can give a statistical measure of the linked between the repeated measurements of the sampling units with the same instrument or individual. The correlation analysis among 2 variables cannot interfere a cause-effect relationship. One variable cannot be used to predict the value of the variable taken from first-time assessments. The least-square regression can be employed to determine and test a significant linear relationship between disease assessments by various raters and statistical relationship among related assessments done by the same individual. Regression-equation parameters like slope and intercept can be used to evaluate and also compare the precision and accuracy of the disease assessment methods and raters. The slopes which are different from one may indicate the presence of bias among the rates. The intercepts are different from zero can indicate the availability of the constant source of error in the raters.

7.3.1 Distribution The spatial distribution of the units in a pathosystem can be a crucial factor which might affect the field estimation of the intensity of any disease. The spatial distribution comprises the method in which the lesions were distributed in the healthy units. The distribution of the diseased units can be regular, aggregated or random. In the case of randomly distributed disease, the variance can be equal to mean theoretically. In the case of aggregated patterns, the variance in lesion number per leaf can be greater than the mean of the lesion numbers per leaf. If the regular pattern is present then the variance can be much smaller than the mean. If the number of host units sampled

Sampling

111

were more, then there would be frequency distributions which exhibit the number of the units which are diseased in each severity category which may be determined. The sample frequency distribution can be related to the theoretical distributions by using the goodness-of-fit test and the empirical distribution parameters can be defined. The theoretical distributions that can be applied for biological systems are: negative binomial ones, Gamma, Weibull, Poisson, log normal and normal procedures. The knowledge of such distribution is important in case of designing sampling techniques. If we want to estimate the intensity of a disease per field then the sampling method, sampling fraction, sampling point, sample size and sampling unit are required. In many disease assessments, the sampling unit can be just a plant. Some of the selected parts like leaves can be assessed for the intensity of the diseases. In every field, the number of sampling units must be predetermined and they must give a mean value representative and that can be a sample size. The sample size can be evaluated by cost incurred during sampling and the precision which is a need along with the time available along with the spatial distribution of particular disease. The sample size must be defined empirically. Several sampling methods have been studied for the assessment of the plant disease. The samples can be obtained at specific intervals with lines which are predetermined in the greenhouse or field. They can be one or both diagonals or can have a large Z or W pattern. In case of disease which is randomly distributed, all the stated methods can produce results which can be comparable and there will be reduced variance in the sample mean which can be gained by enhanced sample size. In the case of disease units which are aggregated, the sampling method can be crucial than the size of the sample. The large W or X sampling pattern can be best to the single diagonal.

7.3.2 Monitoring Populations Monitoring the pathogen with the help of spores which are air-borne can be used as one of the measures of disease intensity. This can work as a complement or an alternative for assessment of disease. With present advancements in technology, the spore counts of populations for field disease measurement cannot replace the old methods of evaluating disease severity. The monitoring of populations of pathogens can also serve for many other purposes. The fungicides can still be a key tool for regulating plant pathogens inside the greenhouse. It is crucial to monitor pathogen populations for their resistance to fungicides. Monitoring resistance means testing the organisms for the sensitivity of the target organisms in the populations present in the

112

Greenhouse Pest Management

field. This can be as a result of long-standing surveillance programmes which were conducted over many years and which might have involved several locations. This can be as a result of short-term investigations in individual cases of suspected resistance. Without this promising work, we cannot know anything about the resistance in pathogens of the crop. The monitoring of resistance combined with monitoring changes in case of practical performance can be an important component for integrated resistance management. Many tools were developed for these type of needs. Tool for estimating the resistance of Botrytis cinerea against fungicides was recently developed. The fungicides which were tested were added to the Petri dishes on a selective medium. The plates were then exposed to the interior environment of the greenhouse preferably at midday. The conidia may be released into the air during that time. The plates can be exposed for an hour as per the intensity of a disease in the greenhouse. The plates were then incubated for about 7 days. The counts of Botrytis cinerea colonies present in the media with the fungicides were compared with other plates which were devoid of fungicides. The data which was obtained was used to express a recommendation on the use of fungicide. Final note: This chapter covered various models that can help to estimate various aspects of host-pests to gain a lucid understanding of the mechanisms of pest management.

CHAPTER 8

MONITORING

CONTENTS 8.1 Scouting .......................................................................................... 114 8.2 Passive Scouting............................................................................... 115 8.3 Active Scouting ................................................................................ 116 8.4 Thresholds ....................................................................................... 117 8.5 A Recent Application of Lighting And Pests ...................................... 119

114

Greenhouse Pest Management

8.1 SCOUTING Scouting is also called as monitoring and it is an important part of pest management practice in the case of greenhouse production systems. The process of scouting can control the outbreak of mite and insect pest populations. The main aims of scouting are to reduce the use of pesticides, to determine the effectiveness of management strategies, Population dynamics evaluation and enhanced use of pesticides. The reduced utilization of pesticides such as miticides and insecticides can lower the selection pressure which is on mite and insect pest populations. This can help reduce the populations from gaining resistance. Decreased use of pesticide can permit susceptible species to bypass mortality and can mate with the individuals which are resistant. By this process, there will be sustainment of susceptible genes throughout the mite and insect population. The lowered pesticide use can yield less problem pertaining to phytotoxicity such as plant injury. The effectiveness of the control and sanitation of culture, bio-control, pesticides, physical control and sanitation strategies should be evaluated to know if the present strategies are good to maintain populations of pests well under the level of damage. The tracking of mite and insect pest populations in the growing season will decide if any alterations need to be made for current pest management practices. Mandatory record keeping can enhance the prospects of implementation of best management strategy. It is important to assess the population dynamics which involves enumerating the mite and insect pests. This will let us know that fluctuations and seasonal abundance in a population of the pests, especially in the growing season. Record keeping helps in this process. The time of application of pesticide is another crucial factor which can help fight mite and insect pests with greater effectiveness. A high percentage of mortality can be achieved if the pesticide application is done when there exist susceptible life stages of the pest most likely at the stage of larvae or nymph or in some cases adult. Several materials and supplies are needed to start the scouting process. This process is based on all the aims stated above. The process of scouting and record keeping comprise of colored sticky cards which are generally blue or yellow, wedges made up of potato for larvae of fungus gnat, hand lens of 10X or 16 X, a map of the greenhouse, data sheets, colored flags, and clipboard. The data collected whilst the scouting process should be computerized and incorporated into an excel sheet. It is quintessential to know the techniques involved in the process of scouting. The techniques for scouting can be divided into passive and active.

Monitoring

115

8.2 PASSIVE SCOUTING The passive scouting comprises of traps. They can be sticky cards which are colored mostly blue or yellow in color, wedges made of potato or sticks which can lure or attract insect pests. The sticky cards which are colored can be employed to attract first and then we can capture the adult stages of winged aphids, whiteflies, western flower thrips, shore flies, leafminers and fungus gnats. Blue or yellow sticky cards can have dimensions of 3 inches x 5 inches. The sticky cards which are yellow in color can attract a diverse variety of flying insect pests like western flower thrips. It is quite easy to identify or demarcate from other objects if yellow sticky cards are used. These cards can allow us to differentiate pests from the growth medium. The sticky cards can be used if western flower thrips are plenty in the greenhouse. The sticky card must be positioned well above the canopy of the crop. The sticky card must be attached to a bamboo stake with the help of a pin. The sticky card can be altered if the crop grows and height increases. The yellow sticky cards can be placed horizontally close to the surface of the growing medium as the adults are active at that place. The sticky cards which are yellow can be positioned on the flat rims or containers. We can use one side of the yellow sticky card in the first week. The unused side can be protected with wax paper which can later be used next week. If the pest number is less because of seasonality or if less number of crops are grown the sticky cards can be changed as we like. The scout must be done once a week. The number of insects which are detected on the sticky cards must be recorded on data sheets. The number of sticky cards differs from place to place in the crop within a greenhouse. The rule of thumb is that one to two sticky cards per 92.9 m2 or 1000ft2 can be practiced. There is a need for more sticky cars if the crop is susceptible to viruses, especially by western flower thrips. In addition to the above, the sticky cards can be positioned close to greenhouse openings like sidewalls, vents and doors. This will help us to identify the migration of insects from the exterior of the greenhouse. If we place the sticky cards near the openings it will be helpful to identify the adult stages of insect pests such as whiteflies, western flower thrips, leafminers and aphids which disperse from the vegetable crops and weeds nearby. The weeds which grow outside the greenhouse can serve as the insect source which can migrate into the greenhouse and must be removed. The sticky cards can be positioned below benches in greenhouses with soil based floors. They can be used for identification species such as western flower

116

Greenhouse Pest Management

thrips, shore flies, and adult fungus gnats. They can assist us to investigate the insect pests which can be pupating in the gravel and soil. The wedges made up of potato or sticks can be employed to know if fungus gnat larvae are present. To make a potato wedge, the potatoes should be cut into quarter-inch pieces which can be placed into the growing medium. They should be allowed to be there for 2 days. The potato wedges are removed and inspected for fungus gnat larvae signs. The number of larvae should be recorded on the data sheet. The potato sticks can be prepared using cut pieces of potato. The pieces will be 3 to 5 inches in length, almost a quarter inch wide. The sticks will be inserted deep into the growing medium so that a quarter inch is visible. These sticks are very effective in scouting especially for fungus gnat larvae which are located much deep. If the plant has extensive root systems, then the potato sticks can be useful. They can also be used to detect gnat larvae of bulb crops like Easter lily or Lilium longiflorum. After 2 days, the potato sticks must be removed. The number of fungus gnat larvae should be counted and the number must be recorded on the data sheet.

8.3 ACTIVE SCOUTING The active scouting techniques comprise of visual inspection. Inspecting for mite and insect pests on the lower side of the leaf is important. The number of plants grown in the greenhouse can be selected randomly or within a growing area. These plants can work as indicators and they should be flagged or marked. They can be used to know the level of pest infestation and it is based on the number of pests available. The number of pests linked with the indicator plant can be recorded on weekly basis and it is based on the growth of the plant, flowering, and temperature which can affect pests at any given point of time. If the crops grown are susceptible to viruses then there should be intensive scouting for inspecting plants and sticky cards two times a week. If we want to save labor costs and time then the scouting efforts should be concentrated on highly susceptible crops. The areas which are closer to vents and doors must be scouted as they harbor and permit winged insects like whiteflies, western flower thrips, and leafminers. The active scouting techniques are good in inspecting pests which cannot fly like western flower thrips larvae, two-spotted spider mites, scales, female mealybugs, wingless aphids and whitefly nymphs. The scouting method can also be called as beat method. This method comprises shaking flowers and leaves over a white sheet of paper with 8.5 inches x 11 inches dimensions.

Monitoring

117

We can account the number of individuals fallen which are moving around. The beat method works fine to investigate populations infested with western flower thrips and two-spotted spider mite.

8.4 THRESHOLDS The thresholds are also called as action thresholds. They are nothing but the number of mite and insect pests which are important to implement certain measures to eradicate problems. The basic principle behind the action thresholds is that there is a certain level of pest tolerance which can effectively reduce the pesticide application frequency and so pesticide resistance. Most of the information can be related to the agriculture cropping systems. They can be used in detecting trends of the pest population in any given growing season, the timing of the pesticide applications and to determine if the pest management practices are really required. If we use action thresholds then we can definitely lower the pesticide inputs. They are dependent on the counts of mite and insects or we can check for plant injury. They can be used if the scouting program is properly established first and then implemented. The first thing we can do is to use blue or yellow sticky cards and in some cases, the ‘beat method’ can be most suited. The ‘beat method’ can give us an accurate assessment of the variations in the population dynamics of larval stages and adult stages of the western flower thrips, especially in greenhouse-grown crops. The action thresholds can be divided basing on the growing season. The counts on the sticky card can be higher during the spring and also in the fall during active mite and insect pests. The management practices must be strengthened that means an incerased number of sticky cards can be used to know the infestation at initial levels. If more sticky cards are used then we can suppress the population of the pests and it yields limited damage to the greenhouse frown horticultural crops. The action thresholds for mite and insect pests of any greenhouse grown plant are much limited as the whole plant is sold and the minute plant damage can be tolerated. The producers should evaluate the count of each sticky card instead of taking the average of the number for each sticky card of the entire section or greenhouse. The data which is related to the average number derived from each sticky card can be used in some cases. The information cannot be useful to detect certain areas which have plenty of mite and insect numbers and this might be useful for the producers to spray pesticides locally instead of their application on a broad scale which is costly. If we use separate counts for each sticky card,

118

Greenhouse Pest Management

then it may permit the producers to know the levels of pest activity and the pests which were coming inside the greenhouse. Several factors can result in erroneous counts on each sticky card. Some plants can attract insects as they differ in their cultivar susceptibility. This can lead to a high number of adult insect pests on each sticky card which is tagged near attractive plants. The flower which is attractive can yield erroneous counts on the sticky card. This is quite common when scouting in case of western flower thrips as they feed, remain in and inhabit on flowers. The sticky cards which are close to doors and vents can capture more insect pests which enter the greenhouses from the outdoors. The age structure is crucial as the insect populations will have both immature and mature stages. These stages are dominant at different time intervals. There might be less number captured from the colored stick card since the immature stages cannot stick to the cards. The color of the sticky card can affect the counts on the sticky card. The western flower thrips can be captured more on sticky cards which are blue and the count density is quite less if the sticky cards are yellow. The placement of sticky cards on crop canopy is also important. The higher number of western flower thrips can be captured on the sticky cards which were placed above the canopy. A high number of fungus gnat adults can be captured on the cards which are placed close to the growing medium. If we remove the plants or cut the flower, then it will create disturbances which can agitate insects. This will make them active and make them dispersed inside the greenhouse so we need more number of sticky cards. Another factor which can directly influence the counts on the sticky card is the horizontal air-flow fans or HAFs. They have the capacity to disperse the insects all over the greenhouse due to the air currents. The problems with the counts of the sticky cards can be avoided if we develop the maps of the entire greenhouse which can also include the position and the location of the sticky card. The action thresholds can be applicable in the case of the cropping systems which are perennial. They cannot be feasible in case of greenhouse systems which have a lower tolerance for mite and insect pests. There can be some problems if we attempt to correlate with actual insect populations with sticky card counts. All greenhouses can have a certain level of mite and insect activity. As long as these pests are low, it is quite a difficult task to justify direct costs, labor and time needed in pesticide application. The producers spend almost 95% of the total time to reduce just 5% of the pest population in their respective greenhouses. Scouting can be a key method of knowing the

Monitoring

119

number of mite and insect pests in the growing season and it can indirectly explain the effective management strategies to control pests. The producers need to establish realistic action thresholds which can be based on the cropping systems so that there will be improved strategies and decisions for pest management.

8.5 A RECENT APPLICATION OF LIGHTING AND PESTS The production of plants at higher amounts and quality has seen much investment from new greenhouse lighting technology. For instance, the boreal and temperate zones see the use of light manipulation of light using high-pressure sodium lamps (HPSLs). Such an artificial environment has been playing a role on the mites or insects that reside on plants. Light or visual signals are utilized by arthropods to target hosts or mates or potential prey. Several taxa are involved as beneficial and pest species such as Prostigmata, Mesostigmata, Thysanoptera, Hemiptera, Heteroptera, Diptera, Lepidoptera and Hymenoptera. Table 8.2: Light and connection with insects Species Myzus persicae Bombus terrestris Frankliniella occidentalis Encarsia formosa Tetranychus urticae

Sensitivity maximum (nm) 530 328, 428, 536 UV, 540 340, 520 375, 525

Several systems such as light-emitting diodes are used; the intensity of which can be adjusted. For photosynthesis and growth, the wavelengths are red, far-red and blue. LED lamps with red and/or blue lighting have seen much research for use commercially. UV light has been shown to be vital for various biological activities in the case of hymenopteran parasitoids and pests like whiteflies, thrips and aphids. The amount of diseases transmitted by these insects has been found to be lowered by blocking UV light from greenhouses. Another example is the use of point LEDs on sticky traps that can control the population of whiteflies. Integrated pest management strategies can see an adaptation of methods that use light to modify the environment that requires a comprehension of pest and biological control

120

Greenhouse Pest Management

agents. While coloured traps and UV absorbing films have been practically used, more research is warranted to understand the spectral efficiency, the effect of such controls on the rhythm and behavior of pests to achieve an overall pest control. (Reviewed by Johansen et al, 2011).

CHAPTER 9

SANITATION AND CULTURAL CONTROL

CONTENTS 9.1 Introduction ..................................................................................... 122 9.2 Irrigation .......................................................................................... 122 9.3 Fertility ............................................................................................ 122 9.4 Sanitation ........................................................................................ 122

122

Greenhouse Pest Management

9.1 INTRODUCTION The implementation of sanitation and cultural control inside greenhouses will assist to reduce the problems due to mite and insect pests. The sanitation or weed removal and cultural or irrigation and fertility practices are the important means to alleviate problems due to pests in the greenhouse production systems.

9.2 IRRIGATION If we water plants and growth medium in excess, shore flies and fungus gnats will reproduce, develop and survive as they get attracted to moist conditions that is based on age and type. If plants are not watered or underwatered, it results in stress that can enhance susceptibility to certain pests like twospotted spider mite. Overhead irrigation can increase relative humidity. This will reduce the development and reproduction of pest like twospotted spider mite and can dislodge certain insect and mite peat such as aphids and thrips physically.

9.3 FERTILITY If we use excess amounts of fertilizers then there will be over-fertility. This will change the quality of the plant and they can become the best food source for mite and insect pests. These conditions favor enhanced female reproduction, growth and development. The plants which are overfertilized with nitrogen-based fertilizers can stimulate growth. The newly formed young leaves cannot develop waxy layer or epidermis and also contain more amino acids which can permit the mite and insect pests to feed on them with their piercing and sucking type of mouthparts. The enhanced levels of amino acids and succulent growth in plant tissues which is due to an over dose of fertilizers can also improve the reproduction and development of certain mite and insect pests. These plants which were grown can be more susceptible to spider mites, mealybugs, whiteflies, leafminers, scales, and aphids.

9.4 SANITATION The process of sanitation can be considered as the first line of defense in pest management. It can lower the potential problems with mite and insect pests. The effectiveness of biological control or pesticides is dependent

Sanitation and Cultural Control

123

on executing a sanitation program which is stringent. Sanitation can be considered as one of the least expensive practices. This process can be done in general operating hours. The process of sanitation involves removal of plant debris, reducing algae and removal of weeds from outside and inside the greenhouse facility. The weeds which are present outside and inside the greenhouse provides shelter to mite and insect pests like whiteflies, spider mites, thrips, leafminers, and aphids. These weeds permit these pests to disperse and survive on the crop. The weeds which can provide shelter or refuge for these pests include Taraxacum officinale or dandelion, oxalis or Oxalis spp and Sonchus spp or thistle. The Sonchus species can harbor whiteflies and aphids, Oxalis can provide refuge to thrips and dandelion harbors whiteflies. Several weeds can be reservoirs for viruses and they can transmit virus to plants on which they feed. The weeds specifically harbor tospoviruses such as tomato spotted wilt and impatiens necrotic spot viruses. This includes bindweed or Convolvulus spp., pigweed or Amaranthus spp., shepherd’s purse or Capsella bursa-pastoris, oxalis or Oxalis spp., nightshade or Solanum spp.,, lambsquarters or Chenopodium spp. and chickweed or Stellaria media. If the issue of weeds is to be addressed, we should install fabric or landscape barriers under benches which can be geotextile and it may be a nonbiodegradable material which does not allows the weeds from growing from the soil under the benches apart from a possibility of controlling algal growth. There are some herbicides or weed killers which can be used outside and inside of the greenhouse. Caution should be followed when using herbicides especially inside the greenhouse. Herbicide must be applied well before the emergence of the weed and they can be called as pre-emergent herbicide and some herbicides can be applied after the emergence of the weeds, they are called as post-emergent herbicides. It is important to check if the herbicide can injure plant or phytotoxicity. It is better to use herbicides which can be applied as a spray or systemic and check for post-emergent activity especially when the greenhouse is empty. Every time when we use herbicides it is important to carefully read the label for necessary directions prior to loading and mixing. The weeds which are large like 6 inches in height can be removed physically by hand. We need to take care of both the roots and other plant parts of the herbicides. The weed-free areas outside the greenhouse which is about 9.1 m can lower the insect migration like western flower thrips and we can stop a risk of transmission inside the greenhouse. Algae can act as a good substrate for breeding for shore flies and fungus gnats. These should be eliminated from the floors and benches. Avoiding

124

Greenhouse Pest Management

overdosing plants with fertilizers, overwatering and using of well-drained growth medium can solve the problems caused by algae. The growth of algae can be checked by disinfectants with active ingredients. The active ingredients can be quaternary ammonium chloride salts, hydrogen dioxide and hydrogen peroxide. The best method is to pressure wash growth media from the walkways and benches so that the algal buildup can be checked. The plant debris such as flowers, leaves and the growing medium debris can be a good refuge for specific mite and insect pests. The mites and the insect pests can migrate or shift to plant material which is fresh when the plant debris decomposes. The growing medium and plant material debris which are stored in unsealed covers can be a good refuge for pests. When the plant material gets spoiled the adult insects tend to migrate to the main crop. It is important to seal the refuse containers tightly. The leftover growing medium can be a good site for western flower thrips to lay eggs and then pupate. This can see the use of vacuum cleaners or brooms to remove the debris of growing medium and plants. The plants of the old stock and the remnants of the previous crop can act as a good source for mite and insect pests. The old stock plants can serve as reservoirs for viruses which can spread via western flower thrips. It is better to remove such infested plants immediately from the greenhouse. Final note: This chapter covered the essentials of maintaining a hygienic greenhouse with fertilizers and water in optimum amounts. The use of appropriate techniques to remove algae, insects and mites by removing debris and appropriate agents has been covered.

CHAPTER 10

USE OF PESTICIDES

CONTENTS 10.1 Introduction ................................................................................... 126 10.2 Improving Performance.................................................................. 127 10.3 Identification of Pests ..................................................................... 127 10.4 Coverage of Pesticides ................................................................... 127 10.5 Timing ........................................................................................... 128 10.6 Water Quality ................................................................................ 129 10.7 Modes of Action ............................................................................ 130 10.8 Application Technique ................................................................... 131 10.9 Targets .......................................................................................... 131 10.10 Label Rate.................................................................................... 131 10.11 Shelf Life...................................................................................... 132 10.12 Frequency .................................................................................... 132 10.13 Issues With Using Peticides .......................................................... 133 10.14 Operational Factors ..................................................................... 135 10.15 Biological Factors ........................................................................ 135 10.16 Multiple Pests .............................................................................. 139 10.17 Mixture of Pesticides .................................................................... 140

126

Greenhouse Pest Management

10.1 INTRODUCTION The pesticides can be miticides and insecticides and they can be an important part of almost every pest management program in the greenhouse. The pesticides are cheaper and they can be applied easily and proved to be effective. There will be a level of comfort and psychological satisfaction post application of pesticides to reduce mite and insect pests and this is quite different from the biological controls which come with certain levels of uncertainty. The pesticides are generally used to kill mite and insect pests. They also maintain the aesthetic quality of horticultural crops which can be helpful for sales and marketing. The producers generally use pesticides whilst selling the plants and it is due to the fact that the consumers are not attracted to plants which have mites or insects or if there are any symptoms of damage. There are some issues stating that there is low tolerance of insects which harbor disease-causing viruses and this will demand excess pesticide use. Due to strict regulations and laws, the addition of the latest ingredients to the pesticides is limited which can be used in greenhouse otherwise. The horticultural crops which are grown in the greenhouses can be considered as specialty crops. This can be the reason why the registered pesticides which will be used in the greenhouses are costly than those used in regular agricultural crops like rice, cotton, soybean and corn. Different kinds of pesticides which can be used in the greenhouses are of the types: contact, stomach poison, translaminar and systemic. The contact pesticides can kill mite or insect pests via direct contact or when mite or insect pests crawls or walks on the surface treated. The mite or insect pests can walk on the surface which is treated and the residues of the pesticides can take their route into the pest body and to the site of action. The stomach poison pesticide is linked with the insects which feed on the treated leaf surfaces and followed by the ingestion of pesticide residues. The residues can be absorbed via the stomach lining. The insects generally stop feeding for a period of 48 days and eventually they die in about 2 to 4 days. Translaminar pesticides can penetrate into the leaf tissues to form reservoirs of ingredients that provides residual activity against those mites and insect peststhat eat leaves. Systemic pesticides can be applied in a growing medium as granules or drench. The active ingredient will be taken up by the root system of the plant and it gets distributed or translocated to all plant parts. The plants which are grown must have a good root system and they should be healthy so that they can absorb the active ingredients. The systemic pesticides can be applied to stop the infestations which attack mainly the phloem such as leafhoppers, whiteflies, soft scales, mealybugs and aphids. The plants

Use of Pesticides

127

should always be irrigated before the pesticide application as it has a certain turgidity and avoids phytotoxicity or plant injury. Two main classes of pesticides which target insects are used in greenhouses. They are broad-spectrum and narrow-spectrum pesticides. Narrow-spectrum pesticides are also known as selective pesticides. The broad-spectrum pesticides are very active and they attack several mite and insect pests and they can be of good choice if diverse horticultural crops are grown. Narrow-spectrum pesticides are active only on certain mite and insect pests.

10.2 IMPROVING PERFORMANCE It was believed that pesticide suppression led to pesticide resistance. This can be acceptable in some cases but there are several factors which also result in reduced performance of the pesticide. The factors responsible for this reduced performance can range from water quality issues to application techniques. Some of the factors which reduce the performance of the pesticides are described in the following sections.

10.3 IDENTIFICATION OF PESTS We need to identify mite and insect pests before pesticide selection as some of the pesticides can have a narrow range target on mite and insect pests on which they work. Some registered pesticides can be active on one group of pests like mites and some are active against two insect types like aphids and thrips. It is always important to correctly identify the pest and for that one should always keep reference images handy. Another way is to send samples to a university based or plant diagnostic center. If the pest is identified with extreme confidence then we can select appropriate pesticide. It is crucial to know the life cycle, behavior and biology of a pest as some of the life stages can be positioned on the plants and some of them can be susceptible to pesticides.

10.4 COVERAGE OF PESTICIDES All the plant parts such as flowers stem and leaves are important in reducing mite and insect pest with the help of pesticides via contact. The lower and the upper leaf surfaces should receive a good volume of the spray solution. It is mandatory to determine the pest’s location and spray the pesticides directly to specific plant parts so that we can achieve maximum coverage and so

128

Greenhouse Pest Management

there will be enhanced pesticide effectiveness. Most of the pesticides can have contact activity which can act on most of the life stages such as eggs, larvae or nymphs, pupae followed by adults of pests like twospotted spider mite, sweet potato whitefly, and greenhouse whitefly. Some pesticides can have localized activity or translaminar activity. The solution of the pesticides and their residues can enter the leaf tissues and can act as a reservoir of ingredients which are active in the leaf. The pesticides which have translaminar activity can give supplemental residual activity against mite and insect pests which specifically have piercing and sucking type of mouthparts in cases where residues dries off. The residual activity can be effective for almost 14 days and can also extend up to 40 days. The residual activity is based on the plant type and the pesticide being used. By using spray cards or water sensitive paper we can assess the coverage of the spray by quantifying the droplet deposition and distribution. The water- sensitive strips will turn blue if exposed to water droplets. The spray cards must be distributed randomly in the crop and they should be attached to plants with extreme care. This method must be performed on regular basis to know the density and droplet size. The spray cards will assist us to evaluate the efficiency of the applicator and the performance of the spray equipment. The spray application must be done only when the person spraying it is active and lacks fatigue that leads to insufficient spray and hence less coverage. The application of the pesticide should not be started during heat condition of a day since the discomfort caused can hinder the process leading to lowered spray coverage and phytotoxicity or plant injury. If the pesticide application is made during any time which creates discomfort to the person spraying it may be due to the spraying equipment and personal protective clothing.

10.5 TIMING If the pesticides are applied when the mite and insect pest are in more number, it can lead to a reduced number of pests well below the damaging levels. The applications must be more frequent when spraying on the overlapping generations or multiple age structures. The mite and insect pests can develop into egg and pupae life stages or they may be already be a cause of good plant damage or they could be in plant locations like floral buds then the spray of pesticides will be a task. We need to set the time of pesticide applications only when there is a low number of pests and this

Use of Pesticides

129

information can be received after scouting. The pesticides can be applied in the early morning or in the late afternoon. This is because of the fact that at these times, the mite and insect pests will be active and on the role played by the ambient air temperature. If the pesticides are applied when the pests are inactive, then this can lower the efficacy of the pests in terms of their mortality especially when we use contact pesticides. If the pesticides are applied on sunny and dry days, then there will be rapid drying which can lessen the residual activity and hence lowering the overall effectiveness. If we apply horticultural oils in overcast days, then there will be possible plant injury or phytotoxicity and the material may not dry. Application of pesticides especially in the evening can be good in the summer season. If we apply pesticides in the evening then there will be growth of gray mold or Botrytis cinerea due to the prolonged period of leaf wetness. Drying because of heating or venting and horizontal air flows can create foliar diseases.

10.6 WATER QUALITY Some of the issues linked with water quality and pH can determine the effectiveness of the pesticide. The pH ranges from 1 to 14. If its value is 7 then it is neutral, whereas pH below 7 is acidic and above 7 is basic. The pH can be a logarithmic and the pesticide sensitivity to pH of water can generally increase by a factor of 10 for each pH unit. A pH will value of 6 can be 10 times acidic than a pH whose value is 7. Likewise, a pH of 5 can be 100 times acidic than pH whose value is 7. If a spray solution pH is greater than 7 then there will be alkaline hydrolysis of pesticides leading to chemical degradation. The pesticide molecules get fragmented and they release individual ions which can assemble with ions. The latest combinations formed lack miticidal or insecticidal property and hence, there will be lowered efficacy of pesticide application. If the pH is less than 7, there will be acid hydrolysis of pesticides. The rate of hydrolysis is based on the spray solution and pH of water, chemical properties of pesticide, the time period of the spray solution in its container and the temperature of water. The exposure time of the alkaline spray solution is crucial. The spray released from the nozzle in the first hour is more effective than the spray released in the last hour especially in case of foliar application. If we increase the temperature of the spray solution it doubles the decomposition rates. At pH 9 if the water temperature is 25 degrees, Orthene or acephate can lose half of its activity in 2 days. If the temperature is doubled, the degradation rate can also double. If the spray container is exposed to

130

Greenhouse Pest Management

direct sunlight then there will be fluctuations in the hydrolysis rates. The manufacturers of pesticides can have the information linked with the effect of pH on the pesticide half-life. Half-life can be a time which is needed to hydrolyze half of the active ingredient. It can also be said as the time needed to diminish half of the original strength of pesticide. Insecticides are more prone to alkaline hydrolysis than plant growth regulators and fungicides. If the pH of the spray solution is more than 7 then organophosphates such as chlorpyrifos and acephate, carbamates like methiocarb and pyrethroid classes such as lambda-cyhalothrin, fluvalinate, fenpropathrin, cyfluthrin and bifenthrin are sensitive to alkaline hydrolysis. The organophosphates can degrade slower than the carbamates. It is a good practice to regulate the pH of the spray solution and adjust wisely so that the pesticide is more effective. The optimum pH of 5 and 7 can be best for more pesticides. Many pesticides can work well at neutral pH. If the pH is above seven, then they will take much time to get dissolved. The pH of water pH should be altered carefully and the use of pH paper is not accurate on account of its inability to offer an accuracy of 0.5. The water pH can vary between 6 and 7. Acetic acid can be used to alter the pH to be below 7 with small increments and it can be checked with the help of pH paper. It is important not to avoid adding vinegar continuously. If the pH must be increased, then we need to add ammonia. The water pH must be adjusted properly prior to the addition of pesticides. The water pH can be altered with the help of adjuvants or water conditioning agents or buffering. The adjuvants can lower the risk of alkaline hydrolysis and so it will be easy to manage pH instead of using sulfuric acid. It is better to add adjuvants to the spray container before adding pesticides. Some of the methods which can avoid the issues linked with pH are not to store pesticides in containers for longer periods, continuously monitor pH and always check the label for precautions.

10.7 MODES OF ACTION The method of pesticide rotation with various modes of action can prevent mite and insect pests to become resistant. If we fail to change the modes of activity, there is a possibility of resistance and hence, there would be a lowered suppression of mite and insect populations. It is better to use a single mode of action within a mite or insect pest generation before opting for another mode of action.

Use of Pesticides

131

10.8 APPLICATION TECHNIQUE Fine sprays and aerosols are effective for winged adults so high volume applications are the best used for immobile life stages and this works well for pests growing in medium like fungus gnats larvae. An aerosol which can be used to kill mite and insect pests in the growing medium, crop canopy and underneath leaves can yield less suppression due to less coverage. The fumigants and aerosols find application on adults. Drenches can be used opposite larval stages which are growing like shore flies and fungus gnats as the pesticide application targets certain life stage like larvae. The application can be applied in low volumes and can be more efficient if the plants are small. If we are dealing with dense crop canopy, then we need to use a high volume of pesticides.

10.9 TARGETS If the susceptible life stages of mite and insect pests are not present then the pest populations cannot be suppressed. The young and immature stages such as nymph and larvae are more susceptible to pesticides rather than pupal and egg stages. Systemic and contact pesticides do not have any activity on the pupae and eggs of insect pests. Suppression cannot be successful if the western flower thrips are in their egg and pupae stages while pesticide application. The young larvae can develop into adults after escaping from the first pesticide application that requires an application of of second pest application. This is common when short residual pesticides are used. Targeting the primary life stages can reduce the frequency of pesticide applications and so there will be lowered selection pressure on mite and insect pests. Careful scouting can help us to know the presence of certain life cycles which are susceptible like larvae, nymphs and adults. So we can apply pesticides accordingly to maximize their effectiveness. If we understand the life cycle, behavior and pest biology then we can easily determine which of the life stages are most susceptible to pesticides.

10.10 LABEL RATE It is better to follow the recommended label rates so that we can achieve the pesticide maximum effectiveness. If we exceed the label rate, it may lead to phytotoxicity and plant injury resulting in economic loss. If we use label rate much lower than recommended then it may result in the failure of pest suppression. Following the label rate strictly can successfully suppress the

132

Greenhouse Pest Management

population of pests. If the rate given on the label is 6-12 fl.oz./100 gal then it is a good practice to use atleast 6 fl.oz./100 gal. We can also use 10 fl.oz./ 100 gal, if needed initially. . In case the the highest label rate is used, there will be an enhancement in selection pressure and hence the resistance can develop faster. The lowest label rate can provide the same effect as a high label rate only if they are applied in the early crop production cycle.

10.11 SHELF LIFE The pesticides cannot last for extended times. The pesticides can be used for a specific period like 3 to 5 years based on the formulation but not after the expiry date. Several pesticides get degraded if exposed to cold or hot extremes. The cold extreme will be around 0 degrees and the hot extreme will be at temperatures greater than 37 degrees. If we stored them in these temperature extremes over prolonged periods, then there will be a diminished efficacy of pesticides. Liquid formulations if stored more than 4 years can get precipitated or get separated out of the solution that will be a hard task to resuspend the active ingredients to be used again. The pesticides must be stored in insulated chambers so that they get protection from extreme environmental conditions such as sunlight and temperature. The optimal conditions for storage of pesticides can be between 600 F and 700F with relative humidity ranging between 40% to 60%.

10.12 FREQUENCY Most of the pesticides kill nymphs and larvae and adults but with no direct effect on eggs and pupae. The pest applications must be repeated in order to kill certain life stages so that the adults who were in their egg and pupae stages during the first pesticide application can be tackled. If we want to tackle with the different age structures and overlapping generations at the same time, then there is a need for repeated pesticide applications. Based on the target and insect pest, at least 2 to 3 applications can be needed in case of abundant pests. The pesticide application frequency can be based on the season. In the case of cold temperatures, the mite and insect life cycle can be for a prolonged period than warmer temperatures and the former requires repeated applications whereas the latter can use fewer applications. The main problem can be with the intervals. If the spray applications are long like 14 days then there will be less suppression of pest populations.

Use of Pesticides

133

10.13 ISSUES WITH USING PETICIDES The property of resistance is an inherited trait. The evolution of resistance in mite and insect populations can be based on the genetic variability and this will allow individuals to survive when exposed to a certain pesticide. The individuals that survived can transfer traits to the next generation that enriches the gene pool with the genes which are resistant. The proportion of the pest population killed or the selection pressure by a pesticide can be a primary factor in addition to the genetic variation in mite and insect population. This is a key to know the susceptibility of a particular pest to the pesticide to affect the resistance developing capacity. If a pest encounters a pesticide, then there will be a selection for resistance which can enhance the proportion or frequency of resistant genes in the pest population. The pest resistance is a global problem since there is global trade for plant material which can disperse mite and insect pests that can also disperse the genes which are resistant harbored by a pest. The pace of development of resistance in a mite or insect populations is based on short development time and high female reproductive capacity. Some of the pests like western flower thrips and twospotted spider mite can have a haplo-diploid breeding system where males have one chromosome set. If any new genetic features arise due to mutation, then there will be an immediate expression of the genes. The haplo-diploid breeding can enhance resistance. The genes linked with resistance can be expressed completely in haploid males especially in the haplo-diploid species. In the case of diploid species, the resistance can be hidden as codominant and recessive traits. An individual cannot become resistant immediately. Due to repeated pesticide applications over several generations, the individuals which are susceptible are removed from the population and the resistant individuals reproduce and breed. This yields individuals of mite and insect populations which cannot be suppressed by a pesticide applied. The resistance can get developed because of the movement of mite and insect pests into and within the greenhouses. There are several ways where the immigration of pests can increase resistance. Firstly, the migration of pests from horticultural crops between the greenhouses and within the greenhouses can enhance resistance since the pests which entered might have been previously exposed to a certain pesticide. The plants received from the distributor might have mites or insect pests which were previously exposed to pesticides and obtained resistance to carry resistant genes. The mite or insect pests which enter the greenhouses from the vegetable grown crops

134

Greenhouse Pest Management

or field grown outside might have been exposed to agricultural pesticides which can be similar to commercially available in greenhouse production systems. Various mechanisms can confer resistance to pest populations of the species which are same. Multiple mechanisms for resistance can coexist in certain mite and insect populations. The mechanisms linked with resistance are metabolic, physiological, physical, behavioral and natural. Metabolic resistance can be by degradation of an ingredient which is active by the activity of pests. If a pesticide gets inside the body, the enzymes detoxify or convert the ingredient which is active into a form which is not toxic. Many enzymes can be involved in the process of detoxification. These enzymes are glutathione S-transferases, hydrolases or carboxylesterases, cytochrome P450 mono-oxygenases or some which are mixed function oxidases. The detoxifying enzymes can transform hydrophobic pesticides into hydrophilic pesticides and these compounds with minimal biologically activity can be eliminated through the excretion. The physiological resistance can also be called as target site insensitivity. It is linked with the interaction and association between pesticide and target. This is almost similar to key –pesticide and lock- target site. There will be decreased binding due to physiological resistance and the pesticide can no longer be active. Some of the pesticides which exhibit such a type of properties are pyrethroid class, carbamate class and organophosphate class. The insect and mite pests can enhance their strength to lower their susceptibility to carbamate and organophosphate. They lower the sensitivity of ACHE or acetylcholinesterase : an enzyme present in the CNS or central nervous system which can be inhibited by carbamate and organophosphate class pesticides. There can be an enhanced ACHE activity. Some of the insect pests can have knockdown resistance or kdr. In this process, the nervous system can decrease the pesticide sensitivity especially for pyrethroid class of chemicals. This is because of the transformations in the sodium channels in the axons of nerve. The axons of nerves can be a good target site for pesticides of pyrethroid class pesticides. The physical resistance is an alteration or modification in the cuticle or skin of an insect which can delay or reduce the pesticide penetration. A delayed absorption via the cuticle can reduce the pesticide concentration at the target. This will prevent an overloading of detoxification system of the pests. The behavioral resistance happens if the mite and insect pests prevent pesticide contact which is linked with the pests which hide in places like terminal points which does not allow pesticides to penetrate. Natural resistance can be called as

Use of Pesticides

135

general resistance which pertains to no susceptibility of pest population to a particular pesticide but already exists and cannot be affiliated with exposure previously. Natural resistance is linked to behavioral, physical, physiological or metabolic traits and some life stages which are not susceptible to a certain pesticide. Most pesticides cannot directly effect on pupa and egg life stages. It is crucial to know the difference between multiple resistances and cross-resistance to understand the complexity involved in resistance. Crossresistance is entirely dependent on a mechanism which confers resistance towards pesticides in the same class which have the same modes of action. The multiple resistance are seen in mite and insect pests that are resistant to one or more pesticides by more than one mechanism. The factors which can affect the resistance rates can develop in the pests and they are classified into operational and biological factors. The operational factors are controlled by greenhouse producers directly. The biological factors can be intrinsic to pest populations.

10.14 OPERATIONAL FACTORS • •

The absence or presence of refuge sites for pests The pesticide relatedness with those which have been applied earlier. • Pesticide application during the susceptible life stages like adult, nymph and larva are not dominant • Mortality levels • The coverage of the spray • The rate of applied pesticide • The frequency of the pesticide applied • The exposure time of a single pesticide The characteristics linked with the residues of the pesticides should be studied. There will be unequal deposition of the spray on the leaves. The proportion of the pest population killed due to pest pesticide should be considered.

10.15 BIOLOGICAL FACTORS • •

The expression of traits or resistant traits due to monogenic or polygenic characteristics The genetic system which includes sexual reproduction, haplo-

Greenhouse Pest Management

136

diploid and parthenogenesis • The pests might feed on a diverse variety of host plants which can permit preadaptation of pests to allow detoxification. • The individuals of the pest population have mobility. • The offspring produced in each generation • Time for each life cycle to complete The development of resistance in a mite or insect pest population can be enhanced in greenhouse conditions. One gene can confer resistance which can yield rapid resistance that is a monogenic character. If more than one gene can yield resistance which might lead to resistance development in a slower pace then it can be due to a polygenic character. The mobility of the pests can be linked with the adults which are winged that disperse to feed or mate in their protected habitats which might affect their pesticide exposure. The environmental parameters like light intensity, relative humidity and temperature are involved in rapid mite and insect pest reproduction and development. Any greenhouse encloses mite and insect pests which can restrict certain individuals which are susceptible from migration. The individuals which are resistant in a mite and insect population can be dominant to continuously breed in the greenhouse. The individuals which are susceptible from the outside areas of the greenhouse and which are not exposed to pesticides cannot enter and has no capacity to breed with the individuals which are resistant. The natural enemies such as predators and parasitoids are generally absent or are present in lower numbers. They cannot enter the greenhouses. Continous annual production can give uninterrupted food to mite and insect pests which can yield several generations during crop production cycle woth frequent pesticide exposure. The management of resistance can be a strategy which can be planned so that it can be effective when pesticides were used. It involves a careful selection of pesticides and linking them with pest management strategies. The management of resistance can be effective to prevent resistance in mite and insect pest populations. The resistance is genetically controlled and the resistance frequency in any pest population can be managed by a resistance management program. Some of the guidelines are • • •

Utilization of pesticides which have broad modes of activity Rotation of pesticides with diverse modes of action Better to use synergists whilst pesticide application

Use of Pesticides

137

• Using natural enemies of pests • Installation of insect screens • Proper sanitation and cultural practices • Scouting crops The pesticides which have broad activity modes can be insecticidal soaps which are potassium salts of fatty acids, spinosad-microbe, fungi and bacteria or beneficial, horticultural oils which can be neem or mineral based and some of the insect growth regulators. Reading of the pesticide label can be useful. It is better to rotate common names like active ingredients but not to use brand or trade names during a resistance management program. It is a good practice to consider the possibility of a pest developing resistance. It is a good idea to formulate rotation programs which utilizes pesticides having diverse modes of action. The mode of activity can be the effect of pesticide on physiological and metabolic processes in mite and insect pests. The whole idea is to rotate pesticides on the basis of various chemical classes but some of the classes have the same mode of activity. Carbamates and organophosphates belong to different chemical classes but they have the same mode of action. These classes can stop ACHE action.. Application of Orthene-acephate followed by methiocard –Mesurol cannot be a good rotation program as they both exhibit analogous action modes. FenazaquinMagus, cyflumetofan-Sultan, tolfenpyrad-Hachi Hachi, bifenazateFloramite, fenpyroximate –Akari, pyridaben-Sanmite and acequinocylShuttle O belong to different classes but they act on the electron transport system of mitochondria which is responsible for energy production. These pesticides target NADH or nicotinamide adenine dinulceotide hydride dehydrogenase –complex I which binds to Q0 center of cyt bc1 or complex-II or complex III or NADH-C0 Q reductase site in the electron transport chain of mitochondria to result in blockade of ATP synthesis. So it is wise not to use pesticides which can act on the electron transport system of mitochondria in succession. Neonicotinoid class comprises various pesticides such as dinotefuran, acetamiprid, thiamethoxam and imidacloprid. All the pesticides of this class exhibit the same modes of action. They bind to postsynaptic nicotinergic Ach receptors resulting in loss of nerve functions. We should avoid these pesticides in succession as it might increase the selection pressure on pest populations and can also lead to resistance. The best strategy is to rotate pesticides with certain modes of action followed by broad modes of activity like insect growth regulators, bacteria,

138

Greenhouse Pest Management

fungi, selective feeding blockers, horticultural oils and insecticidal soaps. The pesticide application with broad modes of activity can minimize the rate of mite and insect pest resistance. It is also crucial to rotate insect growth regulators that have a diverse mode of action, Whiteflies and aphids have shown resistance to several insect growth regulators. The rotation of pesticides containing various modes of action can be done every 2 or 3 weeks. It can be done in between one or two generations of the pest. The rotation of the pesticides depends on the time of the year because the temperature can influence the life cycle of the insect. The high temperatures can be observed in the summer from the mid spring that is dependent on the geographic location. It can shorten the development time of mite and insect pests. It also cause overlapping generations which have variable age structures. Frequent application of pesticides along with rotation can be required in addition to scouting. In winter, the time of development of mite and insect pests will be longer due to lower temperatures. The day lengths are also shorter during winter and we need to decrease the pesticide applications and rotation programs. Combining or mixing pesticides with diverse modes of activity can slow down resistance within the mite and insect populations since the mechanisms needed to combat with mixture may not be available. The individual pests cannot develop resistance to diverse modes of actions at the same time. The pesticide mixtures will be good only if the mite and insect pests are resistant to one pesticide. The pesticide mixtures can help the pests to get resistance to more pesticides which can be called as cross resistance. The pesticide rotation can be a good practice to slow the resistance development in case the pests have various resistance mechanisms. The metabolic mechanisms can confer certain resistance to pesticides which exhibit various modes of action. The rotation process should include many pesticides with diverse modes of action. It can be assumed that the frequency of resistance pests of one pesticide can get decreased during the application of another. The issues linked with resistance can be prevented by non pesticidal approaches. It is best to use pesticides judiciously so that the pesticidal resistance can be mitigated. Due to consumer demanding plants without visible damage and free of mite and insect pests the producers have no choice but to use pesticides frequently that causes more resistance. If the customers are liberal to receive plants with mite and insect pests then there would be limited use of pesticides.

Use of Pesticides

139

10.16 MULTIPLE PESTS The greenhouse producers are dependent on the kind of horticultural crops grown that face a multitude of mite and insect pests. The label rates of the pesticides can differ based on the pest. Application of lower label rates or even less than the rate recommended can yield sublethal effects. This can enhance the resistance potential which is being developed in the pest populations. Application of broad-spectrum pesticides can be useful in tackling competition that can give pest problems. The western flower thrips can consume twospotted mites. If the former is killed by the pesticide then there will a problem with latter. Crops such as poted crops and bedding plants like chrysanthemum or Dendranthema grandiflorum can be attacked by white flies, thrips and aphids at the same time. It is important to design a pesticide program which is effective against one pest but cannot suppress another pest. The management of certain species can influence the management of other mite and insect pests. There is an immediate need to know multiple pest complexes rather than dealing with only one kind of pests. One of the important factors to be considered pertaining to multiple pest complexes is the pesticide resistance. The pesticide resistance can be worsened if the western flower thrips are exposed to pesticides which were sprayed to kill another pest. The pyrethrins used on other pests can result in the spread of western flower thrips as the resistant pests can survive and the natural enemies can get killed or eliminated. Many of the pests are resistant to this insecticide. The resistance can be developed not by the western flower thrips but also other pests. Broad spectrum insecticides can also alter management of white flies and western flower thrips and so they can influence the management of various other pests such as leafminers, white flies and spider mites as the natural enemies will get eliminated. Because of this, there will be a problem with leafminers and spider mites which are secondary pests. Another problem occurs if a pesticide contains two label rates for two pests like leafminers and western flower thrips. The label rate specified can be higher for one pest than the other. In that case, if we use higher label rate to combat one insect pest then we may put selection pressure on the other pest which is to be controlled that can result in an enhancement in the rate of resistance. It is advised to use pesticides which have same label rates for more mite and insect pests. The plant growth regulators and fungicides can influence pest management of mite and insect pests directly or indirectly. The isolation of individual mite and insect pests must be avoided and a

140

Greenhouse Pest Management

knowledge of this pest complex must be developed. One of the best methods to combat multiple pest complexes is by mixing two pesticides to formulate pesticide mixtures.

10.17 MIXTURE OF PESTICIDES The pesticide mixtures can be done by tank mixing two or more pesticides so as to yield a spray solution. The mixture forces the pest population to get exposed to various ingredients at the same time so that the pests can be suppressed. They are many benefits linked with pesticide mixtures but many issues must be considered prior to its use. It is always the best practice to read the pesticide label properly and know why and how they should be mixed. The pesticide mixtures must be used which have a desired mode of action on various developmental stages on which it can be active. Tank mixing of two miticides which can control the twospotted spider mite by killing adult might not be the best choice since both miticides can have the capacity to kill adults and the eggs, nymphs and larvae are safe. Tank mixing of a pesticide which is active on nymphs, larvae, and eggs and a pesticide which act on adults can kill all the life stages of two posted spider mite. It is always preferable to use tank mix pesticides which have various modes of action. The primary advantage of mixing pesticides is that it is convenient and less time consuming, labor intensive and cost effective. It is always beneficial to mix because it is quite hard to spray individually which can attract more costs and labor. Other advantage of pest mixing is that there will be enhanced pest suppression. Tank mixing of two pesticides can lead to a higher rate of mortality than its application individually. This process can be called as potentiation or synergism. Synergism is nothing but the approach of combined toxicity of two pesticides which have a greater effect than the sum of the toxicities of each pesticide individually. If one compound has good activity but the other present in the mixture has less activity when applied separately. The latter compound can be called as synergist. Potentiation takes place when one of the pesticides in the mixture increases the activity of another pesticide. Some compounds can act as synergists. They are the adjuvants that can increase the effectiveness of the active ingredient of the pesticide. Piperonyl butoxide or PBO is not a pesticide but with a mix of pyrethrins and pyrethroid based pesticides. PBO can block insect enzymes which have the capability to detoxify the pesticide. Some of the organophosphate class pesticides can be used

Use of Pesticides

141

as synergists, especially for pyrethroid class pesticides. They can bind to certain enzymes which have the capacity to detoxify. They can counteract the pest’s ability to get resistant. Many of the pesticide manufacturers use pyrethroid and organophosphate mixtures to manage mite and insect pests. Some issues in the use of mixes are mixing two or even more than two mixes can decrease the efficacy of the pesticide than when used individually. This can be called as antagonism. Application of pesticides together can also inflict phytotoxicity or plant injury. It is always advisable to read the labels which are to be mixed carefully. It is good to ask the manufacturer in the event of queries. A potential issue pertaining to pesticide mixture is their incompatibility. This can be treated as a physical condition which avoids pesticides from being mixed completely as a spray solution. This can lower the effectiveness and also cause injury to a plant. Incompatibility can occur because of the physical and chemical nature of pesticides, formulation type, water temperature and water impurities. The best way to know the incompatibility between pesticides is to perform a jar test. In this test, we collect a sample from the spray solution into an empty container. We need to allow the solution to remain still for about 15 minutes. If the pesticides are incompatible then there can be a visible separation or in other words observation of layering or crystals or flakes. This test can assess compatibility only but not antagonism or synergism. New cultivars or plant varieties are introduced into the market regularly. These varieties may vary in their response to the mixtures; It is wise to test the pesticide mixtures on 10 plants before application so that we can avoid possible plant injury. If plant injury is visible it is better to avoid such a type of mixtures. The pesticide mixtures carry both advantages and disadvantages. The greenhouse producers generally mix pesticides such as fungicides, miticides and insecticides to lower the labor costs due to multiple spray applications. This can enhance the suppression of mite and insect pests. Caution must be followed while using pesticide mixtures to circumvent the problems such as resistance, phytotoxicity, incompatibility and antagonism. Final note: This chapter covered the various aspects of pesticides in terms of their usage, activity and various factors to be kept in mind to avoid resistance or damage to plants.

CHAPTER 11

BIOLOGICAL CONTROL

CONTENTS 11.1 Introduction ................................................................................... 144 11.2 Advantages .................................................................................... 144 11.3 QC ................................................................................................ 145 11.4 Implementation ............................................................................. 148 11.5 Approaches.................................................................................... 149 11.6 Natural Enemies And Their Types ................................................... 150 11.7 Banker Plants ................................................................................. 153 11.8 Effect Of Environment .................................................................... 155 11.9 Effect Of Plants .............................................................................. 156 11.10 Release Of Natural Enemies......................................................... 158 11.11 Pesticides ..................................................................................... 159

Greenhouse Pest Management

144

11.1 INTRODUCTION Biological control comprises of employing natural enemies or biological control agents like pathogens, predators and parasitoids against pests. The parasites can be parasitic wasps and the pathogens constitute fungi and entomopathogenic nematodes. These agents can successfully suppress or control mite and insect species in greenhouses. Biological control can be considered as a regulatory process. The natural enemies cannot stop the mite and insect populations. The natural enemies get succeed in eliminating mite and insect pests only if they can develop their own population and the pest population is low. The main reason behind the implementation of biological control in greenhouses is that the pests get resistance. In this case, the effectiveness of the pesticide quite low as the pests show acquired resistance towards pesticides due to its previous exposure. It is not correct to think that the cost of using biological control is a costly affair. If we take into consideration the plant safety, work safety, disposal and resistance the biological control is less expensive.

11.2 ADVANTAGES Some of the advantages of biological control in greenhouses are • Minimal cleanup post application • Less equipment needed for application • No issues of resistance to pesticides • Negligible phytotoxicity or plant injury and safety issues • Minimal regulations and rules • Minimal exposure risks to customer and worker Some of the disadvantages while using biological control are • • • •

Some quality control issues linked with natural enemies Shorter shelf life The cost of purchasing natural enemies is high Specificity problems may occur when tackling with mite and insect pests at the same time • Less availability of natural enemies • Minimal regulation of mite and insect pests The natural enemies of poor quality cannot control the pest populations.

Biological Control

145

11.3 QC Quality control (QC) can be a key component in the biological control program and its success. The biological control can be successful only if the natural enemies which are of good quality are released into the greenhouse environment. The quality of the natural enemies is based on the growing conditions, survival during their transport, packaging and handling by the producer of greenhouse. The natural enemies can be grown in colonies under laboratory conditions. They generally feed on honey water or sugarwater solution or the prey which feed on plants. There are several problems whilst rearing these species. Diseases and molds can contaminate colonies that causes reduced colony vigor and viability. The fitness and vigor of the natural like parasitoids can get affected whilst rearing in artificial conditions. This is because the relative humidity, photoperiod and temperatures in lab conditions can choose populations which can succeed. When these species are released into the greenhouse environment, due to variation in temperatures they will have shorter life spans. The parasitoids cannot locate their prey since the parasitoids were grown in cages where they can find their prey easily and this results in altered foraging behavior. Uninterrupted rearing of parasitoids can affect the sex ratios which can be skewed towards males or females. The parasitoids which have been grown and adapted to lab conditions can mate repeatedly with females so they will have more eggs. The greenhouse conditions can be quite different which can impact the success of the biological program in the long run. The natural enemies fail to maintain the pest populations well below the damaging levels. In the process of growing natural enemies, there will be introduction of hyperparasites. The wild types may be interposed inside the colony. The hyperparasites can be parasitoids and they can use parasitoids as host. The hyperparasites can lower the quality of a colony. The natural enemies can be collected from the colonies being reared and they can be transported to the greenhouse producer. The companies which are called biological control companies can be responsible for rearing, supplying and dispersal or distribution of natural enemies. These companies can be distributors or suppliers/producers or both. The distributors cannot rear their natural enemies so they order them from asupplier/producer. The producers can have the infrastructure to rear several types of natural enemies. They can be transported to distributors if requested. Growing of the natural enemies can be costly given the labor and space involved. This is in the case when they are reared on the pest which feed on their host plants. Mostly the natural enemies can feed on alternate food or on other

146

Greenhouse Pest Management

prey which feed on their hosts. The economic method is to use artificial diets as a supplemental food source for natural enemies. The artificial diets require less space and there will be quality problems due to dietary effects. Due to this problem, the natural enemies cannot perform well when released into the greenhouse. This can be due to altered forage behavior and insensitivity towards chemicals like semiochemicals. The semiochemicals are the chemicals which help in communication among insects. If they were grown for long-term in the lab conditions using artificial diets then there will be a problem for them to identify their targets. The egg laying capacity can be affected by food quality. The parasitoid should be fed with carbohydraterich diet which can be helpful for flight. The female parasitoids must be mated previously and there should be in their preoviposition period before their release into the greenhouse. The variations between the greenhouse and laboratory environment can yield good natural enemy variability. Growing of natural enemies in lab conditions can be good if we consider space and environmental conditions such as relative humidity, photoperiod and temperature. The problems linked with performance in greenhouse can occur if the growing conditions vary. The natural enemies which grow on unnatural prey can be influenced in terms of effectiveness and quality as they have inadequate nutrients or insensitivity to identify prey as no odors are present. The quality control of these natural enemies can be crucial in mass rearing to sustain genetic variability. The diseases caused due to protozoa, viruses, bacteria and fungi can affect the quality of natural enemies such as predators and parasitoids. The diseases can be expressed due to stress for a longer period. The natural enemies can be infected with a disease which can exhibit reduced performance and higher mortalities when compared with disease free natural enemies. Release of infected natural enemies can infect pathogen which can result in insufficient regulation. Predatory mite or Phytoseiulus persimilis can get infected with protozoa. Because of this they lay less egg and the survival rated drop down. The microsporidia can lower the forage behavior and fecundity of the predatory mite or Neoseiulis cucumeris. The mass rearing of Encarisa Formosa or whitefly parasitoid can enhance the susceptibility to microsporidia and hence there will be decrease in the parasitoid ability to control whitefly. Continuous rearing in the lab environment can also yield localized overcrowding or temporary starvation. This will create stress on the natural enemies leading

Biological Control

147

to susceptibility to diseases. Such parasitoid crowding can yield stressful conditions which can enhance the susceptibility to bacteria and fungi. If the natural enemies were infected there suffer from lowered fecundity, attack rates, foraging behavior and longevity. The natural enemies when stressed by insufficient rearing conditions cannot reproduce normally that results in enhanced susceptibility towards diseases. The natural enemies may leave the supplier/producer in good condition but if there exists improper shipping and inefficient procedures are in place then there will be reduced quality of natural enemies prior to release. Exposure to cold or hot extremes and inefficient handling can reduce the performance of natural enemies in the greenhouse. Inadequate shipping conditions can lead to injured or dead natural enemies. This can drastically influence the success of biological control. The containers within which the natural enemies are being shipped should provide complete environmental conditions such as ample air exchange, relative humidity and temperature. The natural enemies must be shipped in a container which is packed with newspaper or Styrofoam peanuts to reduce movement while the transit. Ice pack must be placed in the shipping container to keep the natural enemies at cold temperatures whilst shipping. The natural enemies which were packed without proper precautions can yield stress and hence it lowers their effectiveness. While shipping, several natural enemies cannot have a good food supply that can lower the survival rates. The survival rate can be high if they are transported as pupae and eggs. The natural enemies should be shipped with a good carrier so the consignment can be received the following day. If the transportation time is long then there will be enhanced mortality of natural enemies and less fitness persists and therefore the ability of the natural enemies to control mite and pest population goes down. Any glitches which can delay the shipment can lead to mortality due to desiccation or cannibalism. When predatory mite or Phytoseiulus perimilis is packed and shipped in the form of granular carriers and if the shipping is delayed then they are susceptible to desiccation and cannibalism. If this species is transported without prey, delays in shipping can force them to feed on nymphs and eggs. The predators and parasitoids must be stored for a shorter time after their arrival. Storage for periods longer than 7days can reduce forage ability and fitness. The natural enemies which were stored in their adult stages can be more liable to fitness reduction than those preserved as pupae and immature. The natural enemies must be released immediately upon their

148

Greenhouse Pest Management

arrival in the greenhouse. It is important to check if the natural enemies are alive and this process must be done to ensure that the natural enemies are in good state. It is better to ensure flying adult parasitoids and predators in the form of larvae moving actively. If the natural enemies of poor quality are permitted into greenhouse there will be an insufficient regulation of mite and pest populations which can lead to frustration among the greenhouse producers. The quality of Phytoseiulus persimilis shipped in containers that contain vermiculite or bran. We can check with a small sample on a paper and with the help of a lens we can know that the predatory mites are viable and active. The natural enemies which were transported as pupae and eggs can be screened by a different method. The quality of whitefly parasitoids like Eretmocerus eremicus and Encarsia Formosa which are shipped can be checked. They can be checked on paper cards which contain pupae of parasitized whitefly. A simple card is placed inside a plastic or glass jar closed with a lid. We need to regularly monitor and ensure that there are emerging adults. The original number of parasitoids that emerge can be counted later once they die inside the container. It is essential to assess beneficial nematodes such as Steinernema feltiae or entomopathogenic nematodes before use. This can be done by using a glass jar or even a beaker. We need to collect a minute sample of nematode solution. The jar or beaker must be kept in such a way that the sample is completely exposed to the sunlight or light source. The activity of nematodes moving must be observed. If we notice that the nematodes are rigid and straight or floating in the solution, then we can assume that the nematodes are dead.

11.4 IMPLEMENTATION Before taking any decision pertaining to the implementation of a biological control program it is crucial to know if natural enemies of pests are available from distributors and suppliers. It is also important to know the biology, behavior and life cycle of mite and insect pests which can feed on horticultural crops grown in a greenhouse. Regularly scouting crops and ordering the natural enemies at least 2 weeks in advance from the suppliers and distributors is warranted. It is a good practice to conduct an annual assessment and follow-up to know the successes and failures. The primary procedure which should be implemented and considered prior to attempt biological control program is to establish a well-planned scouting program which can be reliable. If we need to succeed with abiological control program

Biological Control

149

we need to ensure some points. It is crucial to identify all mite and insect pests such as whiteflies, thrips, mites and aphids. It is a good practice to identify the natural enemies available for a specified mite and insect pests. A good relationship must be established with a reliable distributor or supplier who can supply natural enemies. It is better to control the level of pesticide residues. We need to maintain a clean greenhouse by taking out the weeds and debris from the outside and inside of the greenhouse. We need to place an order for natural enemies before 14 days of their release. We need to assess the quality of the natural enemies and ensure that they are in a viable stage upon arrival. It is a good practice to release the natural enemies upon arrival immediately. These natural enemies can see application in the evening or early morning at prescribed rates. It is better to release or introduce natural enemies before mite and pest populations are plenty and attain outbreak proportions. It is recommended to always release a good number of natural enemies if susceptible life stages are observed, that will help control the mite and insect populations. We need to evaluate the performance of the natural enemies in a given growing season. Some of the reasons which lead to the failure of the biological control program are • • • • • • • • •

Release of natural enemies post application of long-residual pesticide Application of excess natural enemies than required Application of less natural enemies Late release of natural enemies Delayed release of natural enemies after receipt Failure to check the quality of the natural enemies on arrival Failure to order correct natural enemies such as predator or parasitoid No proper scouting system Inefficient identification or pest

11.5 APPROACHES The general type of biological control in greenhouses is called as augmentation. It is a process especially designed to enhance the number of natural enemies by buying them from a distributor or supplier followed by their release into the greenhouse. Two approaches are important. They are

150

Greenhouse Pest Management

inundation and inoculation. Inundation is the process of releasing several natural enemies to suppress mite and insect pests without depending on the next progeny that causes pest suppression. Inoculation is the process in which lesser number of natural enemies is released over extended periods within which the next generation or the progeny can be expected to express some level of pest suppression or regulation.

11.6 NATURAL ENEMIES AND THEIR TYPES The natural enemies can be classified into two categories. They are specialist category and generalist category. The natural enemies of specialist category are parasitoids. They attack or feed on one insect or mite and a life stage which can be adult or nymph or larva or egg. The natural enemies of generalist category attack or feed on variety of mite and insect and they are capable of feeding on various life stages of a prey. Natural enemies are expected to have well established efficiency especially in locating prey in localized areas or patches on plants. If natural enemies need to succeed they must reproduce and should have developmental times starting from egg to adult stage as the next generation. An adult female parasitoid can have the capacity to insert its egg on the body of the insect pest or inside it and the eggs will develop into young larva, which has the strength to feed on the internal contents of the pest. The parasitoids which primarily attack aphids can make the aphids expand in size and they become light brown. They are called as ‘mummified aphids’. The parasitoid larva can develop into pupae and then to adult which has the capability to create an opening in the dead insect. The adult can emerge and mate. The female can attack on the insect pests within the vicinity. The parasitoids cannot kill insects instantly. The parasitoids prefer some life stages of the insect pest species. The characteristic of the parasitoids are they kill the prey on or in which they survive, they live freely in the adult stage as ectoparasitoid or endoparasitoid of prey. They consume usually one prey at a slower pace and can reduce the reproduction, feeding and fitness, and the female can lay about 100 eggs. There will be some specificity with respect to insect species and the life stage that is attacked. The parasitoids can be purchased form distributor or supplier. They are shipped with the help of containers and they are placed in the crops of the greenhouse or simply on the cards adhered to the plants. The predator has a capacity to eat portions of an entire mite or insect pest. Several predators consume on all life stages which may include adults,

Biological Control

151

pupae, nymphs, larvae or eggs. The characteristics of predators are that they feed on or sometimes kill more than one prey. They have free living life stages and there is no pupal stage. They consume or kill the prey instantly. Both the adult and immature are predacious. They consume a variety of preys based on the predator. There are three types of predatory mites. They are designated as type I, II and III. The type I are predator mites are specialists that have the capacity to feed on spider mites which belong to Tetranychidae family like twospotted spider mite. One of the type I predatory mite is Phytoseiulus persimilis. The type II comprises of predatory mites that are selective like Neoseiulus cucumeris and Neoseiulus californicus. They consume on a broad range of prey and are capable of feeding on pollen. Type III predatory mites can feed on a diverse range of prey. This includes cyclamen mites and eriophyid mites like 4 legged cigar shaped mites. Type III predatory mites include Neoseiulus californicus and Amblyseius swirskii. Some predators can overlap with respect to their types. Predatory mites can be used against belowground pests such as fungus gnats and aboveground pests such as twospotted spider mite and western flower thrips. The predatory mites can be purchased from the distributors or suppliers in containers or in holding packets and in sachets which can be adhered to the containers or plants which can be useful as hanging baskets. Beneficial nematodes or entomopathogenic nematodes are roundworms which are microscopic. They make their entry into the larval stages of the insect pest via natural openings like spiracles or breathing ores, anus and mouth. Once the larva enters, the nematode can release bacterium thath can attack midgut with the help of enzymes to destroy proteins. This result in septicemia in about 2 days. The beneficial nematodes need moisture in order to survive. Due to this reason, these nematodes can be used opposite fungus gnat larvae which can sustain the growing medium. Generally used entomopathogenic nematode is Steinernema feltiae. The beneficial fungi or entomopathogenic fungi can be employed as parasitoids which use the insect pest as their food source by eating the inner components of the insect. The entomopathogenic fungi can be applied in the form of spray onto the plant foliage. They can penetrate via cuticle or insect skin with the help of mechanical pressure or through enzyme degradation. Once the insect enters into the host, the entomopathogenic fungus spreads throughout the body cavity such as hemocoel. This can compromise the entire immune system of the pest. The death can happen in 3 to 14 days after the exposure. The list of biocontrol agents which can be used in greenhouses are listed in Table 8.1

152

Greenhouse Pest Management

Table 8.1: List of Biological control agents Name of the pest Whiteflies

Type

Agent

Remarks

Parasitoid

Encarsia Formosa

Whiteflies

Parasitoid

Whiteflies

Predator

Eretmocerus eremicus Amblyseius swirskii

Whiteflies

Predator

Thrips

Predator

Against greenhouse whitefly Against sweet potato whitefly Consume eggs, nymphs and pollen Consume eggs and nymphs Attacks insect larva

Thrips

Predator

Thrips

Predator

Thrips Thrips

Beneficial nematode Predator

Thrips

Predator

Dalotia coriaria

Shore flies

Predator

Dalotia coriaria

Spider mites

Predator

Spider mites

Predator

Stethorus punctillum Phtoseiulus persimilis

Spider mites

Predator

Spider mites

Predator

Spider mites

Predator

Delphastus catalinae Neoseiulus cucumeris Amblyseius swirskii Stratiolaelaps scimitus Steinernema feltiae Orius insidiosus

Amblyseius fallacies Amblyseius californicus Amblyseius andersonii

Attacks both I and II instar larvae Attack pupae in the growing medium Attack pupae in the growing medium Consume adults and larvae Consume pupae in growing medium Larvae and adults are predaceous and can get dispersed Consumes on all life stages Attacks twospotted spider mite under optimal relative humidity and temperatures They can tolerate low temperatures They can tolerate high temperatures Consume spider mites

Biological Control Spider mites

Predator

Galendromus occidentalis

Spider mites

Predator

Feltiella acarisuga

Mealybugs

Predator

Mealybugs

Parasitoid

Mealybugs

Parasitoid

Cryptolaemus montrouzieri Leptomastix dactylopii Anagyrus pseudococci

Leafminers

Parasitoid

Diglyphus isaea

Fungus Gnats

Predator

Stratiolaelaps scimitus

Fungus Gnats

Beneficial nematode

Steinernema feltiae

Fungus Gnats

Predator

Dalotia coriaria

153

Can tolerate high temperature and lower relative humidity Females deposit eggs close to infected areas Minimal effect on long tailed mealybug Attacks III-IV instar larvae of citurs mealybug Can attack II instar and adults of various mealybug Females produces eggs close to larva Consume eggs, larvae and pupae. They can survive for 7 weeks without food Should be employed in the early production cycle of crop Consume eggs and larvae

The death of an insect generally depends on the dose. If higher volumes of fungal spores are used then there will be more rapid kill rates to result in higher mortality. Some of the entomopathogenic fungi hat find application in greenhouses are Isaria fumosoroseus, Metarhizium anisopliae and Beauveria bassiana.

11.7 BANKER PLANTS Banker plants are generally used in the growth and dispersal of the natural enemies like predators and parasitoids to control plant-feeding mites and insects. The main use of a banker plant is to grow prey and to sustain uninterrupted reproduction and natural enemy populations. The banker plant systems can be classified into two types. The first type involves the same mite or insect pest which is in the greenhouse. The second type uses alternate prey that can feed on a plant, which was not grown in the greenhouse. They include winter wheat or Triticum spp. or winter barley or Hordeum vulgare. The alternate prey is the one which gets fed by the natural enemies and also

154

Greenhouse Pest Management

gets used by them for their reproduction. The alternate preys generally used are cereal aphids. They are bird-cherry aphid or Rhopalosiphum padi and corn-leaf aphid or Rhopalosiphum maidis. Banker plants can be successful that is dependent on location. Banker plants must be placed at the ends of the walkways or benches. Aphidius colemani can migrate to 1.98 m from their release point but they exhibit high rates of parasitism much close to their point of release. It is better to distribute a banker plant all over the greenhouse. It is a good recommendation to use 4 to 5 banker plants for every 10000 square feet to get effective parasitism. The common rye or Secale cereale plants can be infected with aphids and they can be used as banker plant systems. The rye plants, which harbor birdcherry aphid, can work as banker plants for Aphidius colemani or aphid parasitoid. This parasitoid can attack aphid species such as potato aphid, foxglove, melon and green peach aphids. The main limitation of rye being used a banker plant is that it is susceptible to western flower thrips and they can act as a reservoir for them. Wheat and Barley can be used as banker plants, they can control aphid populations by allowing growing prey like A. colemani, and the predator aphid called Aphidoletes aphidimyza. Some of the banker plant systems can have a predatory bug like Dicyphus hesperus to grown on Verbascum Thapsus or common mullein plants ,grown in between tomato or Solanum lycopersicum plants in greenhouses to control the whitefly population. Banker plants can be employed to grow predators of the twospotted spider mite. The snap bean or bush or Phaseolus vulgaris infected with twospotted spider mites can act as banker plants for predatory midge or Feltiells acarisuga and predatory mite or Phytoseiulus persimilis. The plants can be spread among crops which can harbor twospotted spider mites in the greenhouse. If we use snap or bush beans there will be some problems associated with western flower thrips which have the capability to migrate from banker plants to the tomato plants. The pest populations can grow on the snap or bush bean plants which are not monitored regularly. The banker plants can be good in situations where corn or Zea mays plants harbor grass mite or Oligonychus pratensis which can act as prey for predatory mite or Neoseiulus californicus. The corn plants should be distributed between the crops so that the predatory mites can move back and forth from the main crops to banker plants and vice versa. Ornamental pepper or Capsicum annuum can be employed as banker plants which can support predatory mite or Amblyseius swirskii populations followed by suppression of silverleaf whitefly or Bemisia tabaci biotype B populations, chilli thrips or

Biological Control

155

Scirtothrips dorsalis and western flower thrips under controlled conditions in the greenhouse. The fundamental components of a banker plant system are the banker plant itself, the natural enemy and alternate prey. One of the main advantages while using banker plant in greenhouses is that these plants can maintain natural enemy populations over prolonged periods. This can drastically decrease the costs incurred in purchasing natural enemies. The banker plants must be used along with pest management strategies. It is a good practice to consult a biological control distributor or supplier for further information about the successful use of banker plants.

11.8 EFFECT OF ENVIRONMENT The environmental conditions existing in the greenhouse are light intensity, photoperiod, relative humidity and temperature. They can impact the influence of the natural enemies which control pest populations by affecting survival, foraging behavior and fecundity. It is mandatory to check the environmental conditions prior to the implementation of any biological control program. The temperature affects the rate of reproduction and development of pests and natural enemies. The low intensity of light can reduce the effectiveness of some natural enemies. The natural enemies must compete with the population of the pests and reproduction so that they can control pest populations. The intrinsic rate of increase of pests and natural enemies should be the same so that sufficient regulation can be achieved. The predatory mite or Phytoseiulus persimilis can be effective in temperatures ranging between 20 to 30 degrees. If the temperature increases above 30 degrees, then there will be a decrease in the searching activity. If the temperature is less than 30 degrees, the time taken for development of twospotted spider mite can be much lesser than Phytoseiulus persimilis. If the relative humidity is less than 40 percent the female fecundity, adult longevity and egg survival of the predatory mite can be affected. If the light intensity is higher, Phtoseiulus persimilis tend to live underside of the leaf and prefer lower plant canopy. This will permit the twospotted spider mite to escape from the attack. The relative humidity can influence the ability of parasitoids to attack its prey. At relative humidity between 50 to 70 percent, the whitefly parasitoid or Encarsia Formosa can exhibit high parasitism. The light intensity and daylength can affect natural enemies. Aphidoletes aphidimyza or aphid predator can enter the resting stage if the day length is less than 12 hours or

156

Greenhouse Pest Management

short day lengths. Neoseiulus cucumeris can enter the resting or diapauses stage in the winter if the temperatures are lower than 21 degrees with a day length less than 15 hours. Encarsia Formosa can exhibit lowered effectiveness in fall months because of the lower light intensities. Eretmocerus eremicus can be effective when compared with Encarsia Formosa even lower light intensities exist in the greenhouse. So it is important to release Encarsia Formosa frequently. The cost of purchasing might be high in case of frequent releases.

11.9 EFFECT OF PLANTS Plants can produce two kinds of defenses. They are extrinsic and intrinsic type of defense. The extrinsic defenses are linked with natural enemies. The plant produces certain volatile compounds called terpenoids, which can attract natural enemies, and these enemies can attack mite and insect pests feeding on plants. The plant responds to mite and insects by emitting the volatiles from the damaged areas. The volatile compounds assist natural enemies to locate prey on different areas of plant. Lima bean or Phaseolus spp. can produce volatiles and emit via leaves, which damaged due to twospotted spider mites in order to attract the predatory mites. This property of plants can enhance the ability of predatory mites to locate the prey on the various parts of plant. These volatiles can assist parasitoids that search for tiny prey, camouflaged or feeding underside the leaf. The compounds can also help predators and parasitoids to determine the difference between noninfested and infested plants. This can enhance the efficiency of natural enemies in locating the prey. The concentration of the volatiles emitted depends on the environmental conditions such as light intensity, day length, mite or insect pest and plant type. Cultural conditions such as water stress can affect the release of volatiles via leaves. The intrinsic defenses are produced in a plant in the form of toxins or chemicals that can affect pest digestion. These defenses can also be produced physically which leads to certain impediments like thickness of cuticle, toughness of leaf, waxiness of leaf and leaf hairs or trichomes. The physical defenses can enhance the time of development of nymphs and larvae and this can increase the exposure so enhanced susceptibility to natural enemies. The thick cuticles or tough leaves can decrease the rates of feeding and there will be a prolonged development time of immature life stages. This can enhance exposure to natural enemies. The ladybird beetles that are natural enemies can fall off plants if there have waxy cuticles that enable aphids

Biological Control

157

to escape. The foliar pubescence or hairs on leaf can negatively influence the effectiveness of predators and parasitoids by slowing their movement to reduce walking speed or cause altered walking patterns. These responses can be linked with density, alignment, length of trichomes. These trichomes can be angled downwards which can act as a physical barrier. They can act as a hook which can entangle natural enemies. They can be glandular which can trap natural enemies by the process of adhesion. The natural enemies can be killed even by direct contact with the toxic fluids. Trichomes can influence the forage behavior like their ability to search and efficiency of predators and parasitoids which can reduce their ability to control the pest populations. Trichomes can impede the ability of natural enemies to search for preys on various parts of plants. The trichome density can negatively influence the exposure or encounter rate. This can compromise the effect of natural enemies in controlling the pest populations. The larva of Coleomegilla maculate which is an aphid predator can fall off of cucumber leaves or Cucumis sativus if they have dense trichomes. This can lower the predator’s ability to locate aphids on various parts of plants. The leaves of Transvaal daisy or Gerbera jamesonii contain tichomes in high densities that lowers the walking speed and the rate of predation of predatory mites such as Amblyseius swirskii, Phytoseiulus persimilis and Neoseiulus cucumeris to alter the ability of these species to control pest population. The honeydew excreted by the insect pests which feed on phloem like whiteflies, soft scales, mealybugs and aphids can get accumulated in higher amounts if the trichome densities on leaves are higher. The honeydew can attract predators and parasitoids that cause the natural enemies to spend longer periods in grooming and preening themselves instead of locating their prey. Some of the cucumber varieties have trichomes, which can disturb parasitism rates due to impairment of searching efficiency. The efficiency of Encarsia formosa against greenhouse whitefly is lower. The trichomes disturb the searching efficiency by altering the walking pattern and speed of the movement. If the trichomes on the leaves are reduced then there would be an enhanced ability of Encarsia formosa to control greenhouse whitefly. The parasitoids can walk with higher speeds if the leaves have less trichomes and this enhances the searching capabilities on cucumber varieties. Encarsia formosa has a capacity to parasitize greenhouse whitefly larvae present on the cucumbers if the leaves have less trichome densities. The use of efficient breeding program for plants must concentrate on producing cultivars that can permit the natural enemies. The leaves of Gerbera jamesonii have trichomes that can influence the effectiveness of both Phytoseiulus persimilis

158

Greenhouse Pest Management

and Encarsia formosa. But Encarsia formosa can face a problem with smooth leaves because walking fast cannot help them to locate the larvae of greenhouse whitefly and hence diminished parasitism rates. The increased walking speed can reduce the parasitoid ability to control greenhouse whitefly causing plant damage. The plants such as tomato or Solanum lycopersicum contains glandular trichomes that can entrap or entangle the natural enemies in exudates or the exudates can get accumulated on the surface of their bodies. The impaired movement of natural enemies can waste time in grooming themselves instead of locating prey. The whitefly parasitoid such as Eretmocerus eremicus can be entrapped in the exudates of trichomes of specific plant types. This will hinder the ability to search for prey or killing them. The glandular trichomes of Nicotiana glutinosa can entangle Encarsia formosa. Potato plants do have large number of trichomes that are glandular and they are less susceptible to aphids that can affect the natural enemies with respect to aphids since they are trapped in the produced exudates. One of the other factors to consider is the effect of flowers on natural enemies. The structural complexity due to sepals and petals of some flowers can affect the success of the natural enemies in controlling pests by giving shelter to prey. This will permit them to escape from the natural enemies.

11.10 RELEASE OF NATURAL ENEMIES Natural enemies are optimally released in the starting stages of crop production cycle so that there will be high effectiveness. It is better to apply them before the outbreak of mite and pest populations. Since the natural enemies have very short shelf life, they should be released immediately into the greenhouse upon their arrival. It is always important to check if the natural enemies are alive prior to their release. There should be a basic understanding of natural enemies and their action on pests under standardized environmental conditions. This helps us to determine the growth and reproduction of mite and insect pests. The life stage of a particular pest which is being attacked by any parasitoid must be studied. By studying this, we can synchronize the pest developmental stages such as adults, pupae, nymphs, larvae and eggs that can be susceptible to a certain parasitoid. The spatial distribution of prey inside a greenhouse can influence the searching capability of some natural enemies and their rates of potential release. The number of predators and parasitoids that are to be released is based on the level of pest in the crop. If excess natural enemies are released

Biological Control

159

then there will be mutual interference. The natural enemies must be released early in the crop production cycle, frequently so that the pest population can be maintained below the damaging levels. It is a good practice to remove yellow sticky cards before the release of predator and parasitoid adults as the adults may get attracted to the yellow sticky cards. Such yellow sticky cards are recommended to be replaced once in a week post release of natural enemies.

11.11 PESTICIDES Only the use of natural enemies cannot be sufficient to suppress mite and insect pests in greenhouses. The natural enemies can be used in conjunction with the reproductive capacity of the mite and insect pests like twospotted spider mite and aphids. There should be an alternate strategy for pest management. This may involve natural enemies along with miticides and insecticides, so that the pests can be linked with selective pesticides. These selective pesticides can be microbes, selective feeding blockers, horticultural oils, insecticidal soaps and insect growth regulators. The selective pesticides can be harmless to natural enemies since they can act only on a narrow range of target pests. However, some selective pesticides can be harmful to some of the natural enemies. They can create sublethal effects like delayed prey development and natural enemy, negative effect on adult emergence and reduced survival rates of the enemy. Some of the harmful effects of pesticides are linked with indirect effects, residual activity, host elimination and direct contact. The indirect effects occur if the pesticide cannot have capacity to kill natural enemy post reproduction, altered foraging behavior, altered sex ratio, and lowered adult longevity and viable eggs laid by the females. Residual activity can be linked with the spray applications which may cause no mortality of natural enemies. Many remnant residues can exhibit repellent activity which can impact the predators and parasitoids in locating their food source. Host elimination is linked with the prey mortality that also involves dying or migration of natural enemies due to paucity of prey. The direct effects involve the direct sprays that can kill the natural enemies. Biological parameters which are linked with the natural enemies which can be influenced indirectly by pesticides are prey acceptance, prey consumption, sex ratio, altered prey searching efficiency, altered feeding behavior, development time, reproduction, orientation behavior, population growth or reduction, emergence rates, parasitism or predation, mobility,

160

Greenhouse Pest Management

fertility or fecundity and longevity. The indirect effects can be more important than direct effects. The indirect effects may lower the forage behavior by impairing the locating capability of enemies. They depend on the pesticide which can be systemic, translaminar, stomach poison and contact. They lower the ability of natural enemies to identify their prey. There can be lowered availability of the prey; reduced female reproductive capacity. They can impact consumption and parasitism. They can influence the natural enemy’s capacity to target prey and stop the natural enemies from population establishment. The susceptibility of a natural enemy to selective pesticide can be influenced by various factors. They are mode of action of a selective pesticide, timing of pesticide application, the rate of application, the development stage of the prey, the life stage of the natural enemy, the type of natural enemy. The selective pesticides can be more specific to mite and insect pests. Wet sprays or direct spray applications of the pesticides like horticultural oils which are mineral based and insecticidal soaps can be harmful to the natural enemies especially parasitoids. The horticultural oils and insecticidal soaps can be less harmful then older pesticides. The use of natural enemies and pesticides in pest management programs at the same time can be variable because of multiple interactions. The interactions can be based on the selective pesticide, development stage of development and the enemy type. The pesticide use along with the natural enemies can be good in case of long-term crops (such as Poinsettia or Euphorbis pulcherrima) which can be grown in a greenhouse. Final note: This chapter covered various aspects of biological pesticides and their usage and application in green houses along with an emphasis on various factors involved.

CHAPTER 12

MANAGEMENT OF A GREENHOUSE

CONTENTS 12.1 Introduction ................................................................................... 162 12.2 Management.................................................................................. 162 12.3 Crop Management ......................................................................... 172 12.4 Crop Environment And Management ............................................. 176

162

Greenhouse Pest Management

12.1 INTRODUCTION Greenhouses can differ in their structural complexity. They can be simple plastic film covered tunnels with almost no ventilation to plastic covered, tall and multispan structures, they may cover many hectares and may be equipped with computer controlled sophisticated environments. Greenhouses have certain climates that are windless, humid, warm and almost rain-free. This environment can be good for several arthropod pests and diseases. The climate inside a greenhouse can establish a continuum with the exterior climate and there will be gradients in carbon dioxide, light, humidity and temperature. Based on the crop requirements, the purpose to exclude pathogens and pests and the purpose to implement biocontrol programmes, these gradients can be altered to some extents by devices like ventilation, heating, cooling, shading and screening. The climate at the plant surface (roots and shoots) is called boundary layer; is crucial in the avoidance of diseases and pests. It may extend to 1 to 2 mm for some of the arthropod pests. For fungi it will be about 30 micrometers and for bacteria it will be much lesser. The microclimate can establish a continuum with the climate in the leaf’s intercellular spaces and with the macroclimate which exists in the greenhouses along with its environs. Most of the stages of arthropods pests and some beneficial insects can enter freely and they may leave the boundary layer if it is not good for their activity. Many microbes can passively enter and leave as water splashed or wind dispersed secondary propagules. In order to escape pathogens and arthropod pests the microclimates of the rhizosphere and phyllosphere should be unfavorable to their own activity. At the same time the biological control organisms can be encouraged and grown in microclimates. The biological control organisms have own predator chains and hyperparasites that act against effective biological control of a crop. They do possess their own adverse environments. It is a challenge to handle boundary layer microclimates without an establishment of a primary pest.

12.2 MANAGEMENT The microclimate, external insect and disease pressures, the structural design, the equipment, which control the climate and the handling skill of workers, can have a major impact on any greenhouse that shows us how to regulate diseases and insects. It is crucial to have the input from a greenhouse manager to ensure that the facilities are designed as per the IPM strategy during operations. When the greenhouse is in full operation, the managers

Management of a Greenhouse

163

must be careful and they need to know the activities outside as well as inside of the greenhouse and the effect on IPM.

12.2.1 Sites Production in a greenhouse can be concentrated in regions between 250 and 650 latitudes. This is because of the presence of moderate climate and highly favorable weather patterns. If we move to the higher latitudes, there will be lower solar irradiance. The day length can be shorter with low temperatures in the winter months that can result in poor growth and enhanced susceptibility to a disease. In these conditions, predatory insects can render the biological control hard. The large energy inputs are required to regulate greenhouse temperatures. The aspect of humidification is important to overcome the drying effect of the prolonged heating. In case of lower latitudes, the solar irradiance is higher that stresses crops that makes them susceptible to a disease. Excess outside ventilation can carry propagules and insect pests with them. Maximum yield in the favorable latitudes can be concentrated in maritime areas. In continental areas, there are large swings in the maximum solar irradiance and outdoor temperature levels on a daily basis. This will produce crop stresses that can render management harder. In summer season, cooling of greenhouses can be hard if the temperature of air is well above the designated greenhouse temperature. If relative humidity is much higher than the evaporative cooling, the efficiency is compromised. In any area, the sites of greenhouse operation can create a noticeable difference in the disease management and handling insect problems. The vegetation and field crops which grow in the close proximity to any greenhouse can produce insect and disease pressure. This is well known if the vegetation and crops are susceptible to the same insect pest and disease as the crop of the greenhouse. The pressure can be much more intensified if the pathogen propagules are stirred up due to field operations or when the crop grown outside is harvested or the insects feeding on them were pressurized to get a new feeding zone. The low temperatures can make the insects to go for warmer climates which can be supplied by greenhouse interiors. If the outdoor temperatures are freezing, arthropod pests and pathogens are affected that would lower pest pressure . The pathogen and insect propagules can be carried via doors and vents by wind into the greenhouses but still several pest problems can be lowered to manageable levels. The crop uniformity and maximizing productivity are related with the maximum light penetration. This means that the east-west orientation

164

Greenhouse Pest Management

is good for gutter-connected complexes and free standing greenhouses. Getting a good lighting uniformity during the entire course of the day can be crucial for IPM. This is due to the fact that the diseases and insects can proliferate on stunted plants and shaded areas. Along with the orientation for good lighting, greenhouses are designed to take advantage of the winds. The higher wind speeds can enhance the loss of heat and there will be increased static pressures opposite which the ventilation fans needs to be operated. The moderate wind velocities that are at right angles to the ridge, side vents and gutter can be optimal for natural movement of air via vents. The environs which are present in the greenhouse can serve as reservoirs for pests and pathogens. The greenhouses can be common in an arable area. The presence of weeds, trash piles and crops related with the greenhouse crops can yield sufficient inoculums followed by infestation by vectors. The entry into the greenhouses can be fast on a massive scale. The dust with wind can carry spores along with bacteria, the air currents without or with force may carry spores and some insects from weeds and trash piles, the water run-off inside the greenhouse may carry soil pathogens like Phytophthora and Pythium species along with chytrid vector viruses, and the dirt carried by workers and machinery may also carry pathogens. A foot bath which is filled with disinfectant may lower the risk if placed near the doorway. The use of whitefly-proof screens may help to prevent most of the insects but they may not control bacteria and fungal spores. The diseases for tomato such as root rot, fusarium crown and verticiuim wilt, canker can be noticed below root vents.

12.2.2 Equipment The structural complexity of any greenhouse operation can increase with time. The old structures can be replaced with latest designs. Once the operations increase in terms of size, the profits will also be reinvested and there will be a need for sophisticated climate control equipment. The plastic covered structures with low cost and low height may give some protection for some time from outdoor pests and weather. However, the lack of any climate control may favor the development of the pest and insects inside. Advanced structures are needed to host the climate control equipment. The trend observed these days is of the greenhouse structural design with large gutter connected complexes with 4 to 5 m heights. Once the size pertaining to operations enhances, and then there will be need to increase the gutter heights by chimney effect that is needed to ventilate these structures. The increased air space in between the greenhouse cover and the crop,

Management of a Greenhouse

165

the uniformity of vertical and horizontal air movement is improved, the gradients in temperature in the canopy of the crop is lowered as well as uniformity of lighting. This increased heights of gutters has proved best for IPM since they enhance the height that pathogen propagules and insects should be transported via vents into the greenhouse. The large complexes and the economics can be feasible to the greenhouse design that favor IPM. In case of large-scale operations, it is important to construct header-house facilities which may stop access to the greenhouse. Separate lunch room, shower, foot baths, refuse facilities and concrete floors might reduce the transport of pathogen propagules and insects into the crop area. The costs incurred due to usage of pressure washing equipment and sterilizing equipment can be justified easily. In case of large scale operations, it is important to have separate propagation facilities designed for the disease free transplants. An increased number of crannies and nooks may create difficulty to prevent disease propagules and insects from large complexes once they have achieved a hold. The radiation transmission characteristics and the tightness of air of the cover materials can have crucial effect on the climate for IPM. The cover material must have high PAR or photosynthetically active radiation transmission to enhance productivity and solar gain. It should also have low IR transmission so that the heat loss due to radiation is reduced. They should have lower UV transmission which may slow the sporulation of fungi. There are no records of such a material which have all these radiation transmission characteristics. Based on the local climate and latitude some of the cover materials were proved to be better than other for favoring IPM. Glass is a preferred cover material at higher latitudes where the winter light levels can be limited and there will be lower outdoor temperatures because it has low IR and high PAR transmission characteristics. Glass can transmit UV radiation that can be necessary for fungal sporulation. It has high air leakage that can result in having lower relative humidity especially during the cold periods with heat demands. In these periods, it is important to humidify the glass greenhouses so that there will be continued activity of biological control organisms. Polythene can be considered as greenhouse cover material especially in the lower latitudes, higher PAR transmission is not needed, and the humidity for IPM is crucial. Some industries use admixtures with polythene films so that the UV radiation which is essential for fungal sporulation can be blocked. The blocking capacity might decrease with aging. The polythene-

166

Greenhouse Pest Management

film equipped greenhouses are much tighter than glass greenhouses and they can provide good relative humidity even during hot periods. In case of cool wet periods, condensation and high humidity underside these films can lead to dripping and disease spread in the crops. Surfactant sprays are used for these films so that the condensation is film-wise and the run-off is at the gutter. The roof arches are used for polyethylene greenhouses which is gothic in shape and they enhance run-off at the gutter and film—wise condensation. The heating system must maintain root zone temperatures and air temperatures to the recommended levels so that there will be an effective IPM program in the greenhouses. The steam pipe heating systems or hot water systems are good in commercial greenhouses. Fan-forced heaters are good for small greenhouses but only help to maintain temperatures above freezing. The heat delivered from a fan-forced unit can be costly and nonuniform over a large scale. With steam heating systems and hot-water the heat can be delivered to the lower portions of the plants with the help of radiation pipes. They run in between the crop rows 15 cm underneath the floor level. The heat pipes must be at low levels and they provide heat to the root zone. It can help in inducing vertical air movement through natural convection. The temperature of the water which gets circulated in the heating pipes can be adjusted from 40 to 90 degree Celsius based on the heating demand. The heat can be applied to the plant base in order to attain uniform distribution of temperature. Steam flow at 100 degree Celsius via steam pipes that is cycled on and off so that the air temperature can be maintained. The cycling process can lead to the non-uniform heating of the plant base to cause high temperature variability for such steam-heated greenhouses. In case of cold weather, the heating pipes surrounding the perimeter and the steam heated greenhouses are needed to avoid the cold spots where diseases may develop. For water-heated greenhouses, a small-bore heating pipe can be used to apply heat at the plant tips in order to enhance growth and avoid condensation on the fruit. Low humidity in a greenhouse can be a main reason for failure of biological control and insect controls in the initial stages of the growing season. The transpiration observed in these crops cannot be adequate and we need to maintain the humidity for optimal activity of biological controls. In case of dry and hot conditions, adding humidity can additionally cause evaporative cooling of air. The best systems, which humidify can create tiny water droplets that evaporate even before they settle on the leaves to supply moisture needed for fungal spore germination. Sonic misting systems require

Management of a Greenhouse

167

compressed air supply and high pressure misting systems are equipped with 10-micrometer nozzles that can produce water droplets of 10-micrometer diameter for humidification of a greenhouse. If these systems are correctly maintained, they are capable of producing fog, which can disperse as water droplets that is evaporated in air. The intake and exhaust of air from the greenhouses can avoid excessive humidity and solar heat gain which may otherwise get accumulated inside. Most of the greenhouse operations can be ventilated naturally and passively via vents in the roofs and side walls. The polyethylene covered structures and small greenhouses may not be equipped with the roof vents can be ventilated with the help of fans. Recently, gutter vent systems have been developed for the greenhouses covered with polyethylene, which can permit them to ventilate passively. The rates of ventilation in case of summer temperature control can be 0.75 to 1 air fluctuations per every hour. The rate of winter ventilation can be typically around 10 to 15% of the summer time needs. The link between the rates of natural ventilation, temperature, wind direction, wind speed, vent geometry and greenhouse geometry is well established. If there are closed vents then the natural convection of air inside may not be enough for ample mixing of air and the mass transport in the canopy. At low wind speeds, the boundary layer resistance of the leaf increases causing reduced transpiration and enhanced relative humidity at the surface of the leaf. In case of large greenhouse complexes, overhead fans can be positioned above the crop so that the horizontal air velocities can be 0.5m/s for ample air mixing, reduce the boundary layer effects. The air pressure fluctuations inside and outside can be important to move air through the greenhouses. In passively and actively ventilated greenhouses, the pressure fluctuations outside and inside are always negative. The air borne pathogens and insects can easily enter the greenhouse if the ventilators and doors are opened in hot weather. We need to exclude disease propagules and pests; it is crucial to maintain positive pressure differential. In case of these ventilation systems, the air can get filtered but the removal of bacterial and fungal spores is impracticable. In case of positive pressure differential there will be less chance for insect and propagules infiltration from the outside via cracks. If any obstructions are present then there will be reduction in the vent openings which results in enhanced pressure differential or lowered air flow via vents. In case screens are placed on the vent openings the vent opening area must be enhanced by a factor which is almost equal to the reciprocal of

168

Greenhouse Pest Management

the free area of the screen so that the pressure differential can be maintained. In case screens are used in greenhouses it is important to construct boxes over vents. Screened-in bays can be used for sufficient intake of air. The use of shade curtains and thermal curtains are good for IPM as they can lower the climate extremes, which may stress the biological controls and crop. Thermal curtains can save energy in winter. They can reduce net radiation from leaves via the cover of the greenhouse to sky. The temperatures of the leaf are high and there will be less condensation on the leaves under thermal curtains. The shading is crucial for of hot climates to lower the solar radiation and stress due to heat on crops. Paints can be used on the outer surface of the cover or shade curtains can be used outside or inside to lower the radiation that can reach the crops. The shading systems which are mobile can be used for acclimatizing biological controls and crops to varying solar radiation conditions. The climate in a greenhouse can be determined by interactions between exterior climate variables, climate control equipment and status of the crop. Due to varying solar energy fluxes the climate can vary rapidly so, the control equipment must be quickly manipulated to manage optimum conditions. The climate control requirements are complex in the modern greenhouses, that can be achieved by computer assisted control systems. The climate control systems were developed in order to satisfy the demands of the operations of the greenhouse. The hardware which is used in the greenhouses can be designed to sustain humidity and higher electrical noise. The humidity and temperature sensing systems can be designed to monitor the exterior and interior climate for purpose of control. These sensors can be protected from the sun and they can be aspirated so the control can be dependent on the measurements of the relative humidity and temperature. The software which is used in the greenhouse computers must be developed specially with fault tolerance and it must be integrated into the climate control equipment. The software must be configured and the control loops for every piece must be tuned with the installer so that the performance can be satisfactory. The greenhouse control software available in the market helps operators to schedule some climate set points that is best for the IPM and thereby production. The actual climate control gained can be limited by its capabilities and the skill and knowledge of the operator.

12.2.3 Screening For the Mediterranean basin, crops require protection from arthropods than

Management of a Greenhouse

169

protecting the same crops from weather. The exclusion of insects must help in lowering the incidence of the crop damage and diseases but theoretically the process of exclusion can be performed by fitting a fabric screen of aperture much smaller than the insect’s width. The insect repellents must have a mesh aperture much smaller than the body of the insects. The screens may reduce the light transmission and may impede ventilation. This can create problems in the management of humidity, temperature and light. The compromise is compulsory in management for survival of crops. The screens cannot eradicate or suppress pests but they exclude majority of them. They should be arranged before the pest appearance and biocontrol measures along with pest control measures must be required. The insect predators and parasitoids which are smaller than prey can immigrate via pest screens. The destructive insecticides must be avoided and biological control of pests must be practiced. The screens can obstruct the process of ventilation and this can result in increased humidity and overheating. The enhanced humidity can demand fungicides frequently than unscreened greenhouse. In order to reduce the harmful effects the producers prefer forced ventilation but this can pull whiteflies via screens. The exhaust air from the screened house can enhance the intake of the minute insects. If we apply positive air pressure there will be pushing of air into the structure via insect proof filter which may lower the influx of the whiteflies. The white screens can lower the immigrant pest populations and they also lower the immigration of arthropods which are beneficial. The exclusion may not be complete in any case. The screens cannot be good as there will be rise in the humidity and temperature that may increase plant stress to lower light and increase disease susceptibility. The access for workers and the machinery can also be hard. Several types of screens and plastic covers were developed to protect crops from the insects. The first challenge for a producer is to match a screen type with populations of the local insect. The woven screens can be manufactured from plain woven plastic yarns. The process of weaving can leave slots or gaps between yarns in the weft and warp. In case of commercial screens, there will be a rectangular slot with width much smaller than the whitefly body. It should allow ample light and air transmission. Elongating slots to improve the ventilation cannot be feasible as the threads may slide apart which may allow the penetration of insects. Bethke and Pain have showed that the screens which were designed to exclude Bemisia tabaci or Gennadius has allowed some and they were not successful to exclude Frankliniella occidentalis or pergande. They were successful in

170

Greenhouse Pest Management

excluding leafhoppers, aphids, leafminers, bettles and moths with retention of pollinators such as bumblebees. The unwoven sheets are produced by porous unwoven polypropylene or polyester of polyethylene, microperforated and clear fabric. All the materials are light and they can be applied loosely over the seeded soil or transplants. There will be no need of mechanical support. They were first used in the open field in the early spring. The spun bonded round covers can increase the growth and yield. They can protect the plants from the insects. A perforated sheet of polypropylene can be used to protect Tomato Yellow Leaf Curl Virus or TYLCV which can be transmitted by B. tabaci. The knitted screen is irregular in shape. The whiteflies cannot be excluded. The slot size of the blocks can be reduced to block whiteflies and the level of ventilation will be at impracticable level. These screens can exclude larger insects. The knitted woven screen is a plastic screen which is a result of knitting and weaving. The slot can be three folds longer than in the slots present in the woven screen. The width is less than the body size of the whitefly. The insect may not pass but there will be improved ventilation. Lab tests have confirmed that the high blockage capacity of the screen obstructed whiteflies that is also same as the conventional screen. The UV-absorbing plastic sheets are good to protect crops against insect pests and also viral diseases spread via insects. They can control this by modifying the behavior of insects. There is controversy in these claims. These plastic sheets were made available in the market. The sweetpotato whitefly or B. tabaci is a tiny insect about 0.2 mm wide, capable of transmitting TYLCV. It is one of the limiting factors in flower and vegetable production in Israel. The exclusion of these whiteflies can be crucial and as per their strengths the whitefly-proof screens were produced. The rate of exclusion of a whitefly is proportional to the screen’s mesh. The ability of insect’s to pass via any barrier cannot be estimated with only the mesh size and the thoracic width. There will be high rate of penetration of whitefly which may result due to great variability in the samples of the screen which may be from slipping weave. The whitefly proof woven screens aremost popular to exclude whiteflies and even bigger insects. Thrips with a width of 245 micrometer can move freely via this screen. In case of field studies, the greater proportion was excluded due to plastic’s optical features. The western flower thrips can be affected by color. Shading net with aluminium cover has allowed these

Management of a Greenhouse

171

flies freely in the lab tests. The aluminum screens lowered the penetration of thrips of about 55%. This is much more than white colored ones. If an aluminum fabric is positioned surrounding entrance then it can work well.

12.2.4 Operation Careful operation and maintenance of the climate stabilizing equipment is important for healthy crops as it is important to avoid insect and disease problems in a greenhouse. The errors in the control settings or in some cases the failures of the key pieces can result in heavy losses in a span of minutes. Some of the events may not cause damage to the crops immediately but insect and disease problems can be expressed later after some period. The solution for many problems is to go for preventive maintenance programs and employing skilled operators. The alarm systems and backup power units with fuel supplies can be crucial to guard against heavy losses in case of equipment breakdown or interruptions in service. The computer-aided systems has drastically reduced the demand of manual labor in managing the climate control equipment. It is the duty of the greenhouse manager to review climate data collected with a computer on a day-to-day basis. The manager must do certain adjustments and decide set points to keep the climate conditions under control. The humidity and temperature sensors, which were used as basis for all the control in a greenhouse, must be cleaned frequently and checked on monthly basis. The boiler systems have to be on line and must be in top operating condition. The boiler systems must be in condition not only in winter but also in summer months as early mornings may create condensation on the crops. The vents along with the vent drives must be in good working condition. It must be ensured that they open when in need and can also get closed in case of heavy winds to avoid damage. The misting systems need water treatment programs to avoid nozzle blockage. The mechanisms for shade and thermal curtains must be kept in alignment so that the curtains may be quickly deployed without tears or snags of the material. The screens for insects should be repaired in case of damage. They have to be cleaned on regular basis to avoid blockage of air flow and light.

12.2.5 Education In order to achieve an effective IPM program the workers in the greenhouse should be trained so that they can easily identify nutrient deficiencies, insect and disease problems and respond for an appropriate action. Markers,

172

Greenhouse Pest Management

disposal bins, disinfectants and personal protective gear must be made available to the workers for effective engegement in IPM programs. In case of large-scale operations, it is important to have a site map of the greenhouse and a record keeping system so that pest outbreaks and diseases with control actions are recorded for all the staff of the greenhouse. Decision support software programs can help in educating workers and record keeping including the IPM.

12.3 CROP MANAGEMENT 12.3.1 Sanitation Post resistance, prophylaxis can be an effective and economical way of preventing major pest infestations and disease epidemics. It lowers the need of repeated applications of pesticides, risk of pesticide resistance, contamination of produce by pesticide and the environment and operator. Physical screening for immigrant pests with control of insects in the environs and in field crops and weeds can be an effective prophylaxis against insect transmitted diseases and direct damage. Some of the growers depend on the pruning of old crops to perpetuate the biocontrol insect populations. This cannot be an efficient practice as they may constitute a reservoir of nonparasitized pests and pathogens. Introduction of new biocontrol insects is considered as a good practice. The inoculum reduction is one of the crucial factors in early crop management. This can be achieved by techniques such as seed disinfestations, quarantine, use of healthy plants, micropropagation, disposing crop debr0is, solarizing or pasteurizing soil plus soilless media and greenhouse disinfestations along with stakes, trays and benches. The disinfectants can be formalin or formaldehyde and hypochlorites. These materials are phytotoxic and hazardous to humans. Persulphate oxidizing agent can destroy microbes and viruses without any side effects.

12.3.2 Scheduling The process of seeding, sticking cuttings and pricking-out must be done in greenhouses, far from the primary production area. They can be done on slatted benches or mesh which permits bench ventilation. The benches must be placed well above the soil splash and no overhead pots must be present to avoid drainage water fall and contaminated soil. In case of disease risk in case of cool soils transplanting must be delayed. The root zone must be warmed and the mulch materials must be put down later. Some of the risk

Management of a Greenhouse

173

diseases are corky root rot, root rot and fusarium crown. In case of more monocrops grown in a year, the overlapping of transplant production means the pathogen populations gets perpetuated. Special care must be taken to keep the young plants separate. There will be risk of adjoining crops which can be reservoirs of pests and pathogens.

12.3.3 Spacing Close vertical and horizontal spacing of plants on the bench and in the ground bed may allow rapid spread of walking insects from one plant to another. The pathogen mainly affecting crop in this style are Botrytis cinerea and downy mildew, Clavibacter michiganensis and Pythium spp. The main agents of virus spread are soil and water splash, contaminated fingers, tools, workers and insects. The air movement is generally restricted in case of dense plantings there will be restricted airborne propagules which gives a patchy distribution of insects and diseases. The close spacing can create competition for carbon dioxide, light, nutrients and water as well as damage due to workers.

12.3.4 Medium The growing media can have wide range of substrates. They can be soilmix- soil composts and organic materials like coconut fiber and saw dust. The inorganic materials can be synthetic foams and rockwool along with nutrient film technique or NFT. Soil borne diseases can be common in soil less substrates too than in soil. All the substrates should be free of pathogens and insects at the planting stage and they should be maintained likewise throughout the life of a crop creating a huge demand for hygiene. The soils can be amended with straw, crop residues, farmyard manure and peat. Rotovating and ploughing the soil should be done to reach the root debris and organic matter. The pathogen propagules can be exposed to biological control naturally. The improvement of the soil is dependent on water content, aeration and optimum temperature. The soils harbor many insects like pupae of thrips and leafminers, shore fly larvae and fungus gnat. These species harbor Fusarium spp and Pythium spp. The populations of microarthropods can be determined by the pore size, soil type and soil organic matter. The populations of non-cryptostigmatic mites and collembolan can be increased by organic matter. Fungal parasites, which attack insects and nematodes, grow in the soil. Meloidogyne incognita or root-knot nematode can live at 1-2m below

174

Greenhouse Pest Management

soil disturbance levels. Many of the substrates can be heat-sterilized or fumigated with the help of pasteurization at about 700C. Sterilization at 550C is good as it saves thermophilic biocontrol organisms. The entire greenhouse must be closed in case of sunny conditions for solarization of superstructure and substrate. High temperatures and Vapor pressure deficit in case of closed greenhouses may destroy the western flower thrip and its predator Neoseiculus . The soilless cultivation can eliminate soil borne pathogens. NFT, rockwool and other substrates are not free from the soil borne pathogens. Shore flies are present in the water pools on plastic sheets. Thrips, leafminers and fungus gnats can be present in the rockwool. Covering soil with plastic sheet can have gaps around the stem. The displacement and tears and instantly permit access to insects.

12.3.5 Nutrition Deficiencies, excess of the micro and macronutrients and imbalances in fertilizer use can predispose some of the plants to most of the diseases. The fertilizers can enhance the foliage density and the fruit, flower may get affected to lower yield and it may lower the VPD or vapor pressure deficit in the boundary layer by restricting wind-assisted evaporation and transpiration and so increased risk of infection. When excess nitrogen rates in fertilizers are used there is an enhancement in foliage density and softness and increased susceptibility to flower and leaf pathogens. Hobbs and Waters observed that there is an increase in the B.cinerea or grey mold in chrysanthemum flowers supplied with nitrogen of 6 g/m2. If the nitrate nitrogen compounds are limed then we can use that to control fusarium wilt of many crops. Due to involvement in the cell wall integrity, calcium imparts some resistance that is balanced with potassium in high ratio. Low calcium and potassium ratio allows susceptibility to B.cinerea in tomato crops. The potassium and nitrogen ratio can be crucial in deciding the susceptibility of tomato stems to softrot bacterium. The soft-rot incidence is high at 1:1 K:N ratio that drastically drops if 2:1 and 4:1 ratios are used. Higher soil nitrogen can impede the progress of latent lesions of B.cinerea in case of tomato plants and it may be due to stem senescence. If the foliage is over-luxuriant then it may be conducive to damage by sap-sucking insects like aphids.

12.3.6 Pruning The process of pruning and training tall crops supported by wires such as cucumbers, tomatoes and peppers alter the microclimate by changing the

Management of a Greenhouse

175

spacing parameter. The pruning can change the fruit-foliage ratio and may also affect the source-sink relationships in photosynthesis and susceptibility of diseases of different tissues. If we remove leaves which bear pre-pupal and pupal stages of the pests then we can lower their population. If we remove leaves that are premature and carry eggs then we compromise biocontrol.

12.3.7 Fruit load The distribution of photosynthates in luxuriant crop plants can be related with the tissue susceptibility to bacterial and fungal pathogens. Due to modern technology, an enhanced yield of vegetables in the greenhouses is possible. The source-sink stresses especially on the cultivars haven’t changed much. Diseases like Penicillium stem, fruit rot, root rot and Fusarium crown have become serious in the last two decades. Grainger has reported plunderable carbohydrates that can be available to some pathogens and they were called as high sugar pathogens like B.cinerea. Fusarium spp can be called as low sugar pathogens, which can infest on tissues limited with photosynthates. It is crucial to the producer to maintain nutrition, pruning of foliage, fruit and light in balanced partition so the yield might not be compromised.

12.3.8 Pesticide management The pesticides can be an important component for integrated pest management systems when used freely rather than judiciously. They are considered as significant agents of stress. The over-use of these pesticides may lead to resistance problems. They interfere with microbes, biocontrol organisms of insects, bee pollinators and may enhance iatrogenic diseases. These diseases might be controlled by biological controls if pesticides weren’t present. The pesticides in the greenhouse cannot degrade causing persistence hence; the edible produce will be at risk. Due to this situation, the workers will also be exposed to higher pesticide concentrations. There is no economic threshold of insect pests and populations and the producer must depend on his own experience and his advisors. It is hard to forecast the disease epidemics due to complex sequence of the pathogen life cycles and dependance on the microclimate succession. The use of fungicides is seen when hours of the needed microclimate are utilized for the germination of spores.

176

Greenhouse Pest Management

12.4 CROP ENVIRONMENT AND MANAGEMENT 12.4.1 Temperature Diseases and arthropods have optimum temperatures for their spread and development. Different temperatures can affect different stages of the growth processes in case of grey mold. The growth stages can be sclerotium germination, sclerotium formation, appressorium formation, germ tube growth, conidium germination, sporulation and growth of mycelium. All these stages have different temperature optima. They lie above the optimum range for the development of grey mould which is around 20 0C. The temperatures of fruit and leaves can differ from ambient air temperatures as decided by greenhouse instruments. The temperature in the boundary layer can be different. During night, the energy can be lost by radiation from the leaves and this will result in a drop of one to three degrees of ambient air temperatures and this may also reach dew point. In crops that transpire well, evaporative cooling can lower the temperature of the leaf. The leaves which are insolated and are not transpiring can be warmer than the ambient air. Schroeder showed that the temperature of the red tomato fruits increased from 20 to 50 degrees in air that rose from 26 to 37 degrees. The green fruits which were exposed to the same conditions were cooler. The temperatures of the fruit, flower and leaves can be lowered by shading and evaporating cooling supported by forced airflow and ventilation. Eden showed that the rise in temperatures of flowers can avoid grey molds. In case of high temperatures, there will be more flowers infected with B.cinerea which affects the main stem to cause severe disease. The higher temperatures yielded few infections of the wounds on the stem than at 15 degrees. Eden showed the varying balances between host defense reactions and fungal aggression reactions. The corky root rot was avoided by growing the tomato plants in warmer media. Most of the greenhouse pests are thermophilic and they grow well in 20 to 30 degrees at night. The optimal temperatures for greenhouse whitefly and aphids can be between 15 to 25 degrees. The interaction between VPD and temperature on the survival of thrips was shown by Shipp and Gillespie. The temperature affects arthropod pests and natural enemies. The natural enemies can poorly perform in high temperatures and cold temperatures which generally occur in summer and winter in the Mediterranean area. The temperature tolerant Diglyphus isaea can be used according to the thermal regimes of the greenhouse. Excess heat with higher VPD can be a problem

Management of a Greenhouse

177

to Phytoseiulus persimilis in warm areas. Shipp and van Houten explained the optimum temperatures and VPD for N.cucumeris in cucumber grown houses.

12.4.2 Humidity The effects due to humidity on the crops grown in greenhouses were reviewed by Grange and Hand in 1987. The direct and indirect effects of humidity on many diseases were explained by Jarvis in 1992. Uncertainty about temperatures and VPD in the boundary layer increases suspicion concerning the validity of many experiments on the infective capabilities of the fungal spores and disease prediction systems. Bacterial and fungal spores need a wet substrate in order to initiate infection. Water formed on the leaves and fruits are provided by overhead irrigation, guttation and dew. The fogging systems are needed to cool air with the help of evaporation if the droplets evaporate prior to landing on the plants. Measuring the appearance and disappearance of the dew is hard if there are no sensors which may alter the microclimate of the boundary layer due to heat conduction and shading. Wei designed a copper-plated polyamide film sensor that is wrapped around the tomato fruit with a response time of few seconds from dry to wet followed by response of about 2 minutes to Peltier cooling of the surface to the dew point. This device with microclimate modifiers can alleviate the infection risk. Predicting the formation of condensation and evaporation can be hard while using the atmospheric variables like radiation, air speed and relative humidity. These predictions have errors of about 0.8h. It cannot be accepted in cucumber crop when infected with Didymella bryoniae. Modeling the timing of the dew in outside environment was done but with higher difference between observed and predicted duration of the wetness. The temperature of dewpoint of the air drops below the temperature of the plants and they gets covered with water films and droplets, Wei developed a model from heat transfer theory which can accurately simulate condensation and evaporation from the fruits of tomato while still intact. Wei has reached an agreement between simulated fruit surface temperatures during evaporation and condensation. Wei attained a standard deviation of about 0.40C. The model was successful in predicting wetness within 5 minutes of detection and dryness was forecasted as predicted. The precision gave ample time for any preventive action which is to be done opposite many fungal infections. The presence of free water with

178

Greenhouse Pest Management

lower VPD must be prevented if pathogens are present. These conditions are to be maintained in order to establish epidemics of insect fungal pathogens such as Verticillium lecanii and Paecilomyces fumosoroseus. Varying indications have been yielded for arthropods and their predators. The spider mites can be active at high temperatures and lower VPD. Their predator such as P.persimilis can be avoided in the same conditions. The optimum humidity conditions for the activity of the predators on N. cucumeris were established by Shipp and van Houten.

12.4.3 Water Stress If the rate of water supply which is pumped osmotically by the roots exceeds the rate of water lost due to transpiration, then guttation occurs. To avoid guttation the osmotic potential of the xylem of the root should be negative when compared with the nutrient solution. In case of poorly managed greenhouses the process of guttation occurs at night at low root temperatures and VPD in order to maintain the root pressure and metabolic activity. The tissue can be waterlogged which can be called as oedema and water gets guttated from the stomata, hydathodes in the leaf margins with remarkable effects on phylloplane microbes. Water spreads on the surface and substomatal vesicles which can favor bacterial entry into leaves as in Pelargonim spp. If the transpiration is resumed there will be resorption of water. Wilson explained that the reversal of transpiration allows conidia of B.cinerea which can take their path towards the xylem of the stem in tomato and it remain as latent inoculum. Water can be evaporating and accumulating from the hydrothodes can leave deposits of salts which are toxic in nature. This can be an entry point for the necrotrophic pathogens. The lesions found in case of gummy stem blight can originate from such entry points on the leaves of cucumber.

12.4.4 Light Apart from the day length, the photosynthetically active radiation or PAR (a portion of the spectrum: between 400 to 700 nanometers) can have a huge effect on the crop growth and thereby productivity. The lower and higher light intensities can be key agents that induce stress on the crops resulting in physiological strains which forces crops towards disease. The effect of light in coalition with relative susceptibility of various tissues to disease, partition of assimilates, nutrition and irrigation, pruning and training systems, row orientation and plant spacing can have profound effect on plant

Management of a Greenhouse

179

growth. Day length can be a key in determining diapauses in arthropod and predators. The diapauses can be major limitation in their application. The non-diapausing strain can overcome this situation. Light can impose direct effects on the sclerotium formation, germination and fungal sporulation. Most of the isolates of B.cinerea can be stimulated to produce condiia by near-UV band of light and this can be reversed by blue light. Some of the isolates can form conidia even in the dark conditions. Almost all the fungal members can grow mycelium in dark. B.cinerea can produce sclerotia in red or yellow light and even in darkness. The sclerotia can get developed if exposed to near-UV light for about 25 minutes. B.cinerea and fungi can go for sporulation in the near-UV light which has forced the manufacturers to produce covering materials which can screen out this band to control disease. Tuller and Peterson showed that the fiberglass can transmit less light with the wavelength of 315 to 400 nm. The main effect of the low radiance which was transmitted via fiberglass can induce needle senescence in case of dense canopies and so they will become susceptible to grey mold. The mean light intensity which has inhibited sporulation exceeded the light intensity which promotes sporulation. The former light intensity is 430 to 90 nm and latter’s light intensity can be from 300 nm to 420 nm. In greenhouses the temperature conditions which ranged from 15 to 200C and RH greater than 900C existed 145 folds longer in the fiberglass than in the case of polythene enclosed houses. The humidity effects can overcome the effects of the light wavelength in trials with various colored cloches which enclosed strawberries. Grey mold can be severe in blue and pink plastic covers if the VPD is lower than colorless plastic or glass. The VPS can be about 0.41 in case of blue or pink covers, in clear plastic the value is 1.14 kPa and for glass, the value is 1.74 kPa. The effects of light cannot be simple. Some attempts were made to exclude near-UV light which can induce sporulation in case of some fungi. Reuveni fused polyethylene with hydroaybenzophenone that increased the ratio of blue light to UV with a lowered the process of sporulation of B.cinerea in case of polystyrene petri dishes. When the treated plastic was used, the grey mold lesions were less in cucumber and tomato than that in the case of untreated plastics. The plastic coverings which can absorb light at about 340 nm can limit the process of sporulation and lower the incidence of the grey mold lesions on tomato and cucumber. The white mold lesions were also controlled. The isolates of Alternaria solani depended on near-UV radiation for the sporulation. Vakalounakis has used vinyl films which can

180

Greenhouse Pest Management

exclude the radiation less than 385 nm to lower the incidence of early blight in case of tomato greenhouses.

12.4.5 Carbon Dioxide and Oxygen The enrichment of carbon dioxide can be considered as a standard procedure in many commercial greenhouses. It involves restriction in ventilation to achieve the carbon dioxide concentrations that are required. If these concentrations are in an order of 1000 ppm, then there will be enhanced danger due to misregulation of low VPD. The carbon dioxide concentration can limit the growth of B.cinerea and it was proved that there was a reduction of about 2 to 3 orders of magnitude in case of carbon dioxide enriched greenhouses. The enhanced incidences of the grey mold can be interpreted as enhanced assimilates levels or can be a dense canopy which have more wet plants. Carbon dioxide is a key component of the rhizosphere area as a product of microbial respiration and root respiration; it can have minimal direct effects on pathogens. Stress can occur due to oxygen deficiency in waterlogged and compacted soils. In case of over-warm hydroponic solutions, there is an increase in solute concentrations and temperatures with reduced solubility of oxygen. Due to increased temperatures, there is a higher microbial and root respiration that can further deplete oxygen tension. The lower oxygen tension can cause the death of the roots to cause host resistance to the pathogens of root.

12.4.6 Air Movement The main purposes of regulating air movement in case of greenhouses is to induce thigmomorphogenesis in bench-grown crops, to assist in the evaporation of the droplets of infection and to reduce the steepness of temperature gradients and vapor pressure deficits. The plant spacing and bench air movement can be important factors in forest seedlings against grey mold. The beneficial effects of the air movement are the pathogen spore dispersal.. Some fungal members like Peronosporales can sporulate on the wet surfaces. The air borne conidia can be liberated from the conidiophores with the help of hygroscopic mechanisms to be dispersed via air currents. These mechanisms can depend on the disturbances in the microenvironment due to worker activity and other agents. The same mechanisms can regulate the dispersal of pathogen spores as well as the bio control fungal spores if the

Management of a Greenhouse

181

control is via enhancement of populations. The air movement affects the transport of spider mites on a web via air and to be trapped by plants nearby. The forced air flows can carry larger insects into the greenhouse. The insect aggregation can be regulated by air born semiochemicals and the pheromone dispersal will be due to air currents which may disturb the mating process of the biological control.

12.4.7 Environmental Factors and Integration The disease epidemics are complex sequences of the biological events with diverse set of environments which may occur in a sequence and they may be coupled with the hosts. Jarvis explained the complexity of these events in grey mold epidemics. Starting with sporulation, the condia are produced at 150C at moderate VPD. They are dispersed with the help of hygroscopic movements of the conidiophores in drastically varying humidity conditions and spread on water splash or air currents. The infection occurs on the wet surfaces which are at temperatures ranging from 15 to 20 degrees. The colonization can be faster at 30 degrees temperature. Marois explained that the epidemics of the grey mold were dependent on the concentration of the inoculums, VPD, relative humidity and temperature.. This relationship was different in summer and winter. It is possible to produce working models pertaining to grey mold epidemics in the case of cucumber, tomatoes and rose. BOTMAN is a valuable epidemic model. This is an integrated chemical and biological control program. It effectively predicts the onset and the course of the epidemics. It can be inefficient if the infection occurs 9 hours in case of grey molds and in case of gummy stem blight in cucumber flowers it is just 1 hour. A four day weather forecast has been successful with this software. In some cases, the time of the data collection can be crucial as by the time of collection the infection would have started. It can be irreversible even if the fungicides are applied. The wetness on the surface can be a crucial factor in case of all infections. The predictions made from variations in ambient and surface temperatures are combined with the help of a data processor. The powdery mildew epidemics can have less complicated sequence of events before infection and are based on the dew deposition. The control of fungus mediated diseases can be achieved by disrupting the pathways existing in their life cycles but no water will be present for germinable spores. The integration of disease and pest control can be through manipulation of the environment that is a high complex problem. Clarke explained a computer

182

Greenhouse Pest Management

managed system and he considered a holistic production system as a six hierarchy factor in which the change in a single level may attack and alter the other five levels. So any alteration in the climate of the greenhouse can bring changes in the efficacy of the pesticides, diseases, vectors, pests and biological control agents as well as profit. There are several electronic decision support systems for different facets of greenhouse pest and disease control along with production strategy. Jacobson designed an expert system, which has pre-set points in case of tomato production. Dayan designed TOMGRO which has the capability of modeling physiological processes in the case of tomato. Martin-Clouaire worked with disease escape in their tomato model. Van Roermund worked with production model that can be added to the disease avoidance model. Clarke and Jewett explained a holistic approach system named Harrow Greenhouse Crop Management System for cucumber and tomato. Apart from supplying blueprints of production, this system supplies user-friendly diagnoses for physiological disorders, biological controls, pests and diseases as well as climate monitoring. This system permits the producer to add economic data for analysis. The conflict resolution can be effectively handled by the experts. The ultimate decision whether to reject or accept rests with the grower. The analysis and use of these computer models depend on computer literacy in producers with some knowledge of plant growth and disease biology. If not the entire modeling processing would be futile.

12.4.8 Environment and Microbes Microclimates for application of the fungal antagonists and parasites are close to that which encourage pathogenic attack. The colonization of phylloplane and rhizosphere is a preferred strategy. Adaptation to the microenvironment is important and it is the key for the entire process. The process of colonization can be attained by improving the indigenous populations of the antagonists of the phylloplane. The use of composts and green manures involve control of the rhizosphere without isolating and introducing antagonists. Hoitink suggested that the circulating hydroponic systems do have antagonist populations that can grow naturally in any disease suppressive system. Final note: This chapter summarized the operations in a greenhouse to limit pests with the use of various systems and computer models.

CHAPTER 13

HOST AND PLANT RESISTANCE

CONTENTS 13.1 Introduction ................................................................................... 184 13.2 Key Terminology ............................................................................ 184 13.3 Mechanisms of Resistance ............................................................. 185 13.4 Genetics ........................................................................................ 187 13.5 Durability ..................................................................................... 188 13.6 Breeding ........................................................................................ 189 13.7 Strategies ....................................................................................... 193 13.8 Advantages and Disadvantages ...................................................... 194 13.9 Current Scenario ............................................................................ 195 13.10 Perspectives ................................................................................. 196

184

Greenhouse Pest Management

13.1 INTRODUCTION The main purpose of exploring host-plant resistance and tolerance is to produce cultivars which can exhibit minute reduction in yields when exposed to diseases and pests. The producers get profit from the yields due to resistant crops, which require negligible pesticides, and the consumers get vegetables with less chemical residuals. The capacity of plants to adapt to biotic and abiotic factors is known. Breeders selected plants, which gave good yields and harbored less number of pests and diseases. Our ancestors have exploited the concept of genetic resistance without knowing it. The selection of plants scientifically was started in 1900 and many varieties have been released until date. It was observed that the genetic resistance has some limits and it can also save the plant from low pest populations. Because of the genetic resistance there will be delayed pest infection. The resistant cultivars may stimulate the selection of the pest populations which can live on resistant cultivars. The host-plant resistance plus other techniques such as weed control, crop rotation within the crops and biological control of pests. The host-plant resistance can be crucial in IPM.

13.2 KEY TERMINOLOGY A host plant can be any species on which or in which another organism grows. A parasite is an organism which can get advantage from the host without giving any benefit to the host. Pathogen is the term applied to viruses, mycoplasmas and fungi. The plant disorders due to a pathogen are called as diseases. Animal pest can damage crops and they can be mites, insects and nematodes. The aggressive strains of any pest are those which can result in dangerous symptoms in the plant genotypes on attack. Any physiological race of a virus, bacteria and fungus with some gens which can allow them to attack certain host genotype can be called as virulent race. An avirulent strain has no capacity to attack the host-plant genotype. Painter described host-plant resistance as the relative amounts of characteristics of a plant which can affect the damage produced by the pest. The host-plant resistance is variable that can be modified by abiotic or biotic factors. It is relative since the measurements ate comparative with the susceptible plants which belong to the same group. The resistance can be measurable since its magnitude can be determined. The resistance can be heritable and it can be controlled by more than one gene. The host resistance is common against several pests and plant species in the world. The host-plant susceptibility can be exceptional in many cases. The combination of barriers to infection

Host and Plant Resistance

185

in several plants with collective effectiveness can give us genotypes varying from highly resistant to highly susceptible. If a pest has no capacity to establish a relation with a particular genotype then the genotype can be called as resistant or immune to the pest. The resistance exhibited by many nonhost plants can show resistance to specific pests. In case a plant expresses little resistance to all races and isolates of a pest then it is called as non-racespecific resistance. If any plant expresses resistance to one isolate or pest race then it is race-specific resistance. A tolerant plant can be colonized by any pest an extent like susceptible plants. There will be reduction in quality and quantity of yield. The tolerance can be conversed as sensitivity. Tomato Yellow Leaf Curl Virus or TYLCV can cause mild to no symptoms in Lycopersicon pimpinellifolium and Lycopersicon chilense. The virus antigen’s concentration is less than 1% to that of the susceptible cultivar.

13.3 MECHANISMS OF RESISTANCE The defense mechanisms of a plant against pest attack are constitutive mechanisms while those induced via the process of infection can be termed as induced mechanisms. The plants can induce certain responses to produce defense chemicals that can be costly in terms of energy requirements. The plants must allocate resources for the purpose of defense only when pest attacks. The chemicals that are produced by any plant can be result of several interactions with pests, which may be toxic to pest and may be toxic to plant itself, which may render it weak even if there is no attack by the pests. The constitutive and induced mechanisms can be chemical or morphological. The waxes which are present on the cuticle can form a hydrophobic surface that can prevent water retention and pest deposition followed by pest germination. This can be considered as morphological constitutive defense mechanism. The thick cuticles can restrict the penetration of pathogens, mites and insects. The thick and tough cell wall of the epidermis can make the entry hard for insect and fungal penetration. The process of suberization and lignifications can provide effective protection. The size and the distribution of the lenticels and stomata can be linked with the resistance to the fungi, bacteria and insects which can enter via these structures. The internal barriers like sclerenchyma cells and leaf vein bundle sheaths can restrict the pathogen spread and avoid the penetration of aphids and whiteflies via phloem. The chemical constitutive defense compounds intercept and interfere with the pest growth and reproduction. The conidia

186

Greenhouse Pest Management

germination can be slowed by the compounds released by the plants. Some internal secretions that are inhibitors include phenolic acids in colored onions and in tomato, it is tomatine. The plant tissue can contain antifungal agents which can be produced by plant metabolism and the concentration and compositions won’t change even when attacked by pests. These compounds were named as phytoanticipins. The phytoalexins can only act when there is an infection. Different types of plants can produce different types of phytoalexins. Fabaceae members can produce isoflavonoids. The members of Solanaceae family can produce sequiterpenes. The damage due to the pests can also induce indirect defense. Indirect defense can enhance the effectiveness of the natural enemies against pests. The plants can react to damage by insects and mite with the release of the volatile compounds which may attract parasitoids and predators. The plant response can be systemic or logical. The chemical and morphologically induced defense mechanisms towards pests can be linked with the hypersensitive response. This is the process wherein there will be necrosis that can be induced with specific elicitors which can interact with receptors of the plant and it can be activated by mites, insects, fungi, bacteria and viruses. The model can be called as elicitor-receptor model. This model was observed in tomato. In tomatoPseudomonas syringae pathosystem the response is evoked by serinethreonine kinase encoded by the resistant plant gene which interacts with the avirulence gene of Pseudomonas. If any virus initiates a hypersensitive response in any resistant plant then the tissues in the vicinity of the site of infection will develop necrotic tissue and this can be called as localized acquired resistance which can stop infection by the same virus. The resistance can be exhibited by the leaves which may not be by the original infecting virus but inductor virus. The phenomenon was called as systemic acquired resistance. This is rare and it does not always protect. The Salicyclic acid and Pathogen-related proteins can be involved in systemic acquired resistance. The variations in plants post damage by stresses and pests can increase or decrease the resistance. The increase in the plant resistance can be called as induced resistance and this can be systemic in general. The resistance can get increased with the magnitude of the injury and can reflect complicated physiological variations, histological variations and cytological variations . The pest feeding activities can generate short-term responses which can affect the pest behavior. The long term responses can differ from leaf abscission to changed morphology. The changed morphology can be increased density of trichomes. The induced

Host and Plant Resistance

187

resistance can be induced by pathogens and can be called as cross protection. It generally occurs if a plant has been inoculated with weak or mild strain of the pathogen prior to attack of a strain. The concurrent protection is that the virus cannot replicate so that it can be detected. The plant viruses can induce resistance against the second virus. The two resistance mechanisms towards insects are antibiosis and antixenosis. The antibiosis is the process where there will be interference with the insect physiology and antixenosis is the process in which the insect behavior is altered. The patterns of egg laying, feeding, probing, landing and approach on a susceptible plant can be disturbed due to resistance and they may induce non-acceptance or non-preference. These disturbances can alter the behavior of the insect and can protect a plant in the starting phases of attack. Plant substances with antifeedant, deterrent and repellant properties were established lately. Various groups of secondary plant compounds which are toxic are terpenoids, flavonoids and alkaloids can have harmful effects on the fertility, generation-time, development and growth of the insects. Some of the morphological characteristics which can interfere or modify the insect behavior are hairiness of stalks and leaves, cuticle wax, shape and color.

13.4 GENETICS The pests and the host plants can coexist even if pests can induce heavy damage on plants shows that both have evolved together and there is a dynamic equilibrium which is established between resistance and virulence. If host-parasite resistance or pest virulence increases without much opposition then a plant or pest might get eliminated. The genetic studies concerning the host-plant resistance is virulence genetics.

13.4.1 Inheritance In segregation of populations, the variations with resistance can be continuous or discontinuous based on the resistance genes involved. The continuous variation from susceptible plants to resistant plants shows that there exists polygenic resistance which is the sum of all the small and individual expressions of several genes. The discontinuous variation can indicate that the resistance can be monogenic or oligogenic and they can be dominant or recessive genes. The individual plants can fall into a defined category of susceptibility or resistance. The genes which produce resistance are clustered in the form of linkage groups or loci which is complex. The

188

Greenhouse Pest Management

first genetic study was reported in the year 1905. Many studies pertaining to resistance have been reported and it was concluded that the genes which confer resistance can be inherited in a simple way. The dominance is a very common character in hypersensitive responses and recessive resistance can be rare. The inter-allelic gene interaction or epistatis is reported in rare cases.

13.4.2 Concept of Gene for Gene Here, the expression of host-plant resistance towards a pest is based on the genotype of the pest. The virulence observed towards a pest is based on the genotype of the host. Flor showed that the gene which gives resistance in plants can have a gene which confers resistance in pest. This relationship was called as gene-for-gene concept. It was observed in many fungal diseases, parasitic plants, insects, nematodes, bacteria and viruses. The interaction generally takes place between the dominant resistant alleles and dominant alleles of avirulence. Any gene is involved if a locus in a pest carries a gene that matches avirulence. The susceptible plants with no resistant genes can be attacked with all the races of the pest. The pests which carry 2 virulence genes can attack plants and are independent of combination of resistance genes. The gene- for –gene interaction can generate absolute resistance or absolute susceptibility of the plant against pest. The race-specific response can be called as vertical resistance, It can be against some genotypes of some pest species. If the resistance is against all the genotypes of the pest with no differential interaction then the resistance can be horizontal resistance or race-non-specific resistance. The concept of gene-for-gene concept is also applied for horizontal resistance that is polygenic in nature.

13.5 DURABILITY The term durable was proposed by Johnson and Law to explain longlasting resistance. It is not that the resistance is effective against all the variants of the pest. It concerns the resistance, which can give control for years and is based on the environmental conditions which can suit the pests. In susceptible cultivars, the pest population can have a set of strains in a dynamic equilibrium. One or maybe two races can predominate. If a resistant cultivar is planted the strains that are predominant then, they may not propagate or the rate of their propagation can be less than the average. If one strain can propagate in the cultivar then the propagation will be high as there is no competition from other strains.

Host and Plant Resistance

189

An outbreak of a pest may occur since the resistance is broken. It is hard to know if the pest population is of mixture of strains or virulent mutants that vanish from the pest populations in the absence of a compatible resistant host plant. Theoretically, the induced resistance can be considered as complete. The predominant strains can be lost for increasing the virulence. The rate of spread will be fast and the introduced resistance can be partial. This is because of the fact that the dominant and virulent strain would compete. At times when Tm-1 which is a resistant cultivar was used the pathogen has spread faster and the TMV race 1 soon predominated. Tm-2 cultivars which are resistant to the TMV race 0 and race 1 were not effective as there was quick spread of TMV race 2 and the cultivars with Tm 1 and 2 were released. The resistance for these cultivars was broken as TMV 1 and 2 races predominated. The case histories of Tm-1-Tm-2 and Tm-1, Tm-2 support the lack of durability hypothesis. Some of the cases where the durable resistance was controlled by major genes are resistant to Cladosporium in cucumber and Stemphylium in tomato. Some of the cases of low durable resistance are Bremia in lettuce and F. fulva. The resistance to insects can be polygenic and partial. Most of the virulent populations or biotypes adapted to the partial resistant cultivars can be selected. The transgenic cultivars with Bt gene depend on monogenic factor which can have high expression. Many insect species such as Helicoverpa can adapt and tolerate toxin produced by Bt gene. The partial resistant cultivars can decrease the selection pressures on the populations and this can slow down the virulent biotypes development. The reproduction type of a pest can affect the durability of the host-plant resistance. The aphids can use their capacity of parthenogenesis to colonize the resistant cultivars and the populations develop quickly to withstand the host-plant resistance. The soil borne pests can spread at a slower pace than airborne pests. It can be inferred that the virulent races or biotypes of pathogens can take more time to colonize the area on which the resistant cultivars are grown. Some of the host-plant resistance types can be more durable than other types. In the case of plant morphology changes, more changes in the pest are required to adapt that can take more time.

13.6 BREEDING The resistant varieties can be generated via breeding programs that can involve a search for resistance offering sources, resistance evaluation and selection of the generations that are segregated. For producers, the pest

190

Greenhouse Pest Management

resistance concerning new varieties can be a sole characteristic. The breeders must consider the agronomic characteristics of a new variety, which is resistant, and it must be better than previous varieties. If this condition is not followed carefully, then there will be an exaggerated growth of the pest population.

13.6.1 Sources In case resistance to a pest is present in cultivars then the source of resistance can be a resistant cultivar which can be same as ideotype. These cultivars comprise of genes which are of high quality and yield resistance against some pests in order to adapt to the greenhouse environments which can be exploited. The first step which breeder must follow is to do some literature search for some plants which were mentioned as a source for resistance. Seeds must be from those source plants to investigate the level of resistance to know if the source plants can be an initial point to start a breeding program. In case the resistance which is desired is not explained, then the breeder can use germplasm banks. The sequence can be landraces followed by wild forms and related species and genera. It can be hardly possible to know the source which may offer high-level resistance in case of germplasm collections. The breeding material can be altered with the help of mutation, molecular genetic techniques and tissue culture in order to generate new varieties. The induced mutations can produce small number of cultivars. Prolonged culture causes genetic variation or somaclonal variation. The beneficial variation as a result of tissue culture can offer resistance to glyphosate which is a pesticide and also to Bipolaris oryzae. In spite of all the benefits, there are some problems concerning somaclonal variations which can produce source of variability. This is due to the instability in the variation. To enhance the variability of a particular species via genetic manipulation some limitations do exist as it is hard to identify and later clone genes. Once the number of the genes which are cloned increases there will be more variability in the process of plant transformation. The viral DNA expression in case of transgenic plants can generate virus resistant plants which can produce new variability into the gene pool.

13.6.2 Evaluation The plant populations can be exposed to a particular pest so that the susceptible and resistant plants can be differentiated fast. The field screening has an advantage in that the cost can be low and the test conditions can

Host and Plant Resistance

191

mimic the native situations where commercial crops grow. The process of field screening has some disadvantages as it depends on the weather and the possibility of the growth of the pest can be uncertain. Other pests can interfere with the tests. The process of screening in controlled conditions like climatized rooms and glasshouses can provide standard environmental conditions and the pest which is present and its distribution can be manipulated and controlled. These conditions of growth cannot be taken as a representative of the same situations in commercial crops, which are to be produced. The expression of resistance in case of host-parasite system can be dynamic based on the composition, the quantity of the inoculums, development stage of the plant and conditions in which the evaluation of the resistance is done. The minute amounts of the inoculums generate less or negligible symptoms in case of susceptible plants and the resistance can be overestimated. In case of Pepper- Phytophthors capsici system, the isolates of concentrations of 102 zoospores/cm3 cannot produce mortality on certain cultivars but if we use 104 zoospores/cm3 then there will be high rate of mortality upto 100%. The breeders generally test the plants soon because the seedlings require minimal space and time in order to develop and they are less resistant. The expression of resistance can be affected by the environmental variables such as soil fertility, temperature, light and the distribution pattern of the plant genotype. In order to calculate resistance, the values of the environmental variables must be in the range of the values of certain conditions in which the commercial crops grow. The host-plant resistance in case of Manduca sexta in the tomato enhances if the plants are grown in long-day-light conditions. The light of low density especially in the cloudy days can reduce the expression of the resistance against insects. The temperatures outside the conditions in which commercial crops are cultivated can lower the expression of resistance in many host-pest systems. Gomez and Tores showed that 3 lines of melon which are grown at normal temperatures can exhibit resistance to Sphaerotheca fusca at about 260C but they exhibit susceptibility at temperatures below 210C. Higher concentrations of nitrogenous fertilizers can enhance the susceptibility and if we apply Phosphorus and Potassium fertilizers there will be increase in resistance. If the resistance of various genotypes was assessed in small plots the resistant genotypes can be able to export minute level of inoculums but they will get high levels of inoculums from the genotypes which are susceptible. So the expressed resistance will be underestimated when compared with the same

192

Greenhouse Pest Management

genotypes which were measured in trials in larger plots. This process can be called as interplot interference. It can be regulated by control cultivars with various levels of resistance that serve as references. In all cases, the minute variations which are visible in the infection levels in small plots must be recorded carefully. The pests which show vertical dispersion can exhibit less interplot interference than pests which exhibit horizontal dispersion. The main application of in vitro resistance screening can be to select cells, calli and somatic embryos which can exhibit resistance to the toxin produced by a pathogen. Some of the advantages of this technique are the uniformity of the environmental conditions which can differentiate minute quantitative variations of the plant resistance. This technique can also take advantage of the somaclonal variation. The haploid cells can make the recessive traits revealed. Large number of the individuals can be processed. The main limitations include that the in-vitro resistance screening cannot identify the defense mechanisms which can be dependent on various tissues. The resistance exhibited at cellular level cannot be expressed across the entire plant. The cells can survive an infection and they can get adapted physiologically and there will be no genetic variants. It is restricted to tests for pathogens that produce toxins.

13.6.3 Methods of Selection It is important to integrate resistance into the agronomic characters, which a cultivar needs to get recognition in the market. The donor of the resistance must be taken into account to improve the genotype of a cultivar for quick resistance introduction. Complete resistance can be managed easily than partial resistance. The complete resistance can be important for the pests which can damage the end-product of the crop. This is due to the fact that the greenhouse produced crop can be of good quality and there should not be any cosmetic damage like scars or spots which can diminish the acceptability of a consumer. Most of the cultivars which are grown in the greenhouses can be hybrids. In order to generate a resistant hybrid the resistance must be introduced into one of the parents which can be called as dominant resistance and they may be introduced into both of the parents which is called as recessive resistance. The selection process for the monogenic resistances can be backcross. In case of polygenic resistances then the process can be recurrent selection. The marker-assisted selection can help recover genes linked to the markers. The markers can be scored easily than the genes responsible for

Host and Plant Resistance

193

resistance. In order to be sure that minor fraction of the individuals which were selected as recombinants, the linkage between target gene and marker especially in the coupling phase is set lower than 5 cM. A repulsion phase marker which is linked at lower than 10cM can yield a higher efficiency than that of 1 cM especially in a coupling-phase linkage. The markerassisted selection doesn’t need inoculation so it can avoid the errors due to unsuccessful infection, resistance and variability of aggressiveness and incomplete penetrance. The breeding for resistance can be done when the inoculations of the healthy plants grown in the field cannot be allowed for safety concerns. The susceptibility of fenthion exhibited by seedlings of tomato can carry Pto gene for resistance can be used as indirect indicator to select for resistance to bacteria. Aps-I is an isozyme marker used commercially for years as a substitute for screening with nematodes in order to select Mi resistance gene in tomato. The Mi genotypes can be selected with the help of PCR based marker and it is tightly linked with Mi than Aps-I. The screening tests which are needed for resistance to many pests can have questionable validity due to the interference by one pest to the infection by others. The marker assisted techniques can prevent infection and they can assist in introducing many genes which are resistant to various pests. This MAS or Marker Assisted Selection has the potential to transfer polygenic resistance as markers with high heritability and the direct selection of resistance genes can be masked due to the environmental effects. In case of tomato, the molecular markers were identified for polygenic and oligogenic resistances. One of the solutions to control the pathogens which can infect roots can be to use resistant rootstocks. They can be used for many greenhouse crops like roses, carnations, cucumbers, water-melons, melons, eggplants and tomatoes. In case of roses the rootstock grafting can be used to enhance the disease resistance and to alter the vigor and thereby longevity of the crop.

13.7 STRATEGIES Many resistant cultivars are dependent on the use of single or major genes and they were proved successful even when there is breakdown of the resistance from time to time. Many strategies are used to reduce the problem of resistance breakdown resistance genes are used. The cultivar mixtures and multilines can be generated from physiologically similar lines or the cultivars that may contain race-specific gene of resistance. There are no

194

Greenhouse Pest Management

cultivar mixes and multilines among the species which are grown in the greenhouses. The gene deployment can use many cultivars with diverse genes of resistance and produced within an area that is clearly defined. In case a pest generates virulent race on the cultivar, another cultivar can carry other gene of resistance in the area from the following year until the virulent race overcomes its resistance. The next cultivar grown will be a first cultivar or it can be a new one with some resistance to the last virulent race. The gene deployment can use the diversity of the host-plant population to stabilize the pest population and prevent a virulent race. To use the gene deployment all the producers of the area must cultivars with the similar resistance gene. The process of pyramiding the resistant genes can involve the introduction into a cultivar of all or many possible genes of interest against a pest. In this process, the pest needs to have many mutations ranging from avirulence to virulence to prevent resistance and the probability of successive mutations can be low and it is the based on the probability of each mutation. The Pto gene protects tomato from P. syringae and some of the resistant cultivars like Pto have been grown. Stockinger and Walling in 1994 showed that the novel genes named Pto-3 and Pto-4 can withstand race0,1. Buonaurio showed that pyramiding Pto, Pto-3 and Pto-4 in one cultivar can give an optimal solution for disease control. The integrated pest management targets pest population and keep them at minimum level. The probability of new pest starins which may emerge can be proportional to the level of the pest population. The integrated pest management can lower the possibility of developing a virulent strain. The durability of the strain specific resistance can be enhanced.

13.8 ADVANTAGES AND DISADVANTAGES Some of the advantages are that the resistant cultivars can be acceptable to the public except transgenic cultivars. The harmful environmental effects can be at the lowest and with reduced pesticide pollution. The resistant cultivars may be incorporated in the IPM or integrated pest management programs and if IPM is combined with biological control it can yield a cumulative effect. The cultivars which are completely resistant don’t require chemicals to control pests and the cultivars which are partially resistant also require less quantities. It is cheaper and the seeds of resistant cultivars are cheaper and almost equivalent to that of the non-resistant cultivars. This technique can be applied easily since the producer needs to buy only resistant cultivars. Some of the limitations of these cultivars are that the pest can

Host and Plant Resistance

195

adapt to the resistance that causes less durability of the resistant cultivars. The resistance should be introduced into every new cultivar. The resistant cultivars may control one pest but pesticides can control many pests. More time is employed for the development of a resistant cultivar.

13.9 CURRENT SCENARIO Pest control with the help of resistant cultivars was a successful approach and new resistant cultivars are available in the seed market from time to time. The crops grown in the greenhouses are candidates for introducing resistance since there will be high income from these crops. Tomato can be considered as an important vegetable and it has been a central focus for several companies. These tomato crops can be crossed with wild species to serve as key source of resistance genes. The resistance for tomato pests is known as some of them were introduced into their cultivars. The cultivars which are commercially available may possess multiple resistances against many diseases. All this resistance can be monogenic and complete. In case of sweet pepper, the sources of resistance were widely available from wild relatives for viruses. The insect pests can be targeted by biological control and therefore breeding for resistance may not be pursued. Sweet pepper, tomato and cucumber have a narrow genetic base. There are no wild relatives which can provide the genes responsible for resistance. Downy-mildew caused by Pseudoperonospora cubensis , Cladosporium cucumerinum and Corynespora cassiicola can inflict serious problems in cucumber. The resistance genes are present but the commercial cultivars have only partial resistance. A combination of biological control, control measures and partial resistance can be a good solution. Melon possesses several varieties that have provided resistanceintroduced in the commercial cultivars. The powdery-mildew can be considered as the main fungal disease in case of greenhouse cultivation and resistant cultivars for the races 1,2 are in the market. The resistance to Papaya Ring Spot Virus or PRSV was bred with melons for subtropical and tropical conditions. Resistance to ZYMV or Zucchini Yellow Mosaic Virus can be race specific and may not be effective against a second viral pathotype. There will be partial resistance to Aphis gossypii which can stop formation of colonies and can lower the incidence of Aphid borne viruses. Lettuce exhibits vast genetic variation and the wild species can carry out crosses with the commercial cultivars. The biological control is hard in case of leaf vegetables due to shorter cropping cycles that hence, requires the use of

196

Greenhouse Pest Management

resistance breeding. The monogenic resistance can be present for Bremia lactucae which is dependent on the gene for gene system and the resistance cannot be durable. In case of floriculture, the resistance breeding is new. Minimal incentives were given to breed the resistant cultivars because of the high cosmetic demands, short span of products and zero tolerance. Many species and some cultivars can be grown on limited acreage and fewer restrictions are imposed on pesticides used in case of floriculture. In case of chrysanthemum, the monogenic resistance for Puccinia horiana is well determined and exploited commercially. The partial resistance against thrips and leafminers was found. Fusarium oxysporum can affect the host season and two races were characterized. The host-plant resistance against race 1 is due to a single gene that is presently injected into commercial cultivars. The host-plant resistance against race 2 is polygenic and it can be expressed if the resistant locus is homozygous or heterozygous for the dominant resistant alleles. The susceptibility may occur if there are more numbers of homozygous recessive alleles. Despite the complex genetic basis of resistance the resistant cultivars with field resistance have seen release.

13.10 PERSPECTIVES The durability pertaining to the resistance may increase if many possible resistance genes are injected into a cultivar. The resistances injected in commercial varieties are mostly monogenic. This is because, to pyramid many resistance genes against one pest is hard and costly. Suitable molecular markers can make this process easier. The improvement of the screening techniques and selection indirectly can make it easier to breed hosts with polygenic resistances. The partial resistance can be controlled by several genes with little individual effects and it can be durable than monogenic resistance which is complete. However, its use is lesser, because it is hard to demarcate and select individual effect of every gene in the case of segregating generations. It is difficult to evaluate the benefit of the partial resistance. It is hard to convince the producers pertaining to the advantages of the resistant cultivars which may exhibit disease symptoms. An amalgamation of partial resistance and biological control can yield necessary control. The public concern pertaining to the pesticide effects have left the government to make stricter laws to regulate the use of pesticides. The use of IPM techniques in greenhouses inclusive of resistant cultivars can circumvent the use of pesticides. The limitations of the resistant cultivars are lesser than their benefits.

CHAPTER 14

DISINFESTATION

CONTENTS 14.1 Introduction ................................................................................... 198 14.2 Steaming........................................................................................ 198 14.3 Fumigation .................................................................................... 199 14.4 Importance of Selective Pesticides ................................................. 201 14.5 Side-Effects .................................................................................... 201 14.6 Tests ............................................................................................... 202 14.7 Effect of Chemical Pesticides on Useful Organisms ........................ 204 14.8 Factors Involved ............................................................................. 205 14.9 Pesticide Resistance And Anti-Resistance ....................................... 207

198

Greenhouse Pest Management

14.1 INTRODUCTION Soil borne pathogens are a severe problem in case of plant protection in greenhouses. This is because of their ability to survive in the soil for many years and they may exist in their dormant or resting stages like microsclerotia or sclerotia, mycelia until the crop becomes susceptible. The structures can withstand against all adverse environmental conditions and applications such as chemical application which can regulate most of the control problems all over the world. The same scenario will hold good for soil borne pests like weeds, parasitic plants, nematodes and arthropods. The process of fumigation can be considered as a key approach to regulate the soil borne pests. The soil solarization or SSOL can be applied to growth media or soil and sometimes in combination with minute doses of the soil fumigants, which can control all the soil borne pathogens effectively.

14.2 STEAMING The process of steaming, overheating, aerated steam and hot water steam was widely used in greenhouses when the growth media is used. Steam has been employed for disinfection of soil since a century. The plant pathogens can be removed by steaming and this is due to the fact that the heating reaches lethal levels. This may cause damage to structures. The steaming can exhibit growth stimulation in the crops. The steaming via Hoddesdon pipes dug into the soil can no longer be used. This condition is also good to increase the temperature to 1000C. The soil preparation must be done carefully that is crucial for better steam penetration. The soil must be tilled as much deeper as possible using a shovel plough and it should be left for drying before steaming. It is crucial to minimize the amount of plant debris when steaming the growth medium. If there is good preparation, then there will be appreciable penetration of steam. This will control the pests in case of heavy soils. This process can hold partial control on light sandy soils. The process of steaming growth substrates like vermiculite and tuff stones can be good. The peat soils can have certain limitations as they have high water content. The soil steaming can be performed by active and passive techniques. In the case of passive steaming, the steam is blown on the surface below a covering sheet. It will be left for heating upper layer. The lower layers are heated with the help of heat transmission. This process will progress till 1000C is attained about a depth of 10 cm. The disinfestation of the deep layers can be partial as in case of sandy soils. The process of active steaming

Disinfestation

199

can be done wither negative or positive pressure. These techniques can use drainage systems as well as pipes laid at about 70 cm depth and 80 cm apart. In the case of positive pressure technique, the steam is blown via holes located near the pipes. The negative pressure can be considered as improved technique. The steam can be passed on to the treated area below the plastic sheeting. There will be even and rapid distribution over the plot surface. This will be followed by active suction into the deeper soil layers with the help of negative pressure via the drainage system. This technique can be cheaper as there will be energy saving which is due to speedier heat transfer..

14.3 FUMIGATION The process of soil fumigation is performed with the application of toxic pesticides to the soils by various methods. The fumigants can migrate down or they may spread across the entire soil profile and they reach the pest organisms directly. As they have higher vapor pressure, they can go for secondary distribution. MBr is the most effective fumigant : that however was reported to cause ozone depletion so it was banned in many states. Some of the other soil fumigants are dichloropropene, formaldehyde and CS2 releasing compounds and MIT or Methyl Isothiocyanate.

14.3.1 MBr (Methyl bromide) It is considered as one of the powerful soil fumigant with a broad activity pectrum. Several soil borne fungi such as Rhizoctonia, Pythium, sclerotium, verticillium, Sclerotina are very sensitive to MBr. Some bacteria like Clavibacter cannot be controlled by MBr. The action of MBr is based on careful the soil preparation and tight covering with plastic. It is applied to the soil at a rate of 110g/m2. This can be done with the help of injection prior to covering. This can also be distribution of hot or cold gas. The duration of the application can be based on the soil temperature. The main problem with MBr is its toxicology which harms a handler with residual bromine in the edible plant parts. MBr has been observed in water close to greenhouses. In 1992 MBr was banned by the Montreal Protocol as it was the major cause for ozone depletion. There are several uses of MBr and post ban there is no known substitute for this fumigant. Efforts are on to lower the MBr dosages and regulate its emission to limit the harm to the environment. Most of the solutions produced are impermeable mulching films. The low and high density polyethylene films were proved as poor barriers as they favor the

200

Greenhouse Pest Management

escape of MBr at greater rates. The pest control can be a factor of pesticide concentration and exposure time. The retention of the MBr in the soil below the impermeable films for extended periods at low MBr amounts. The fungal pathogens such as Fusarium spp can be controlled effectively with the reduced use of the MBr.

14.3.2 MIT Dazomet is a product which can be made available as granules or powder. The chemical is systematically hydrolyzed to 4 subproducts. One of the products named MIT (methyl isothiocyanate) was important. This is active against Vertivillium spp. This fumigant can be employed to control many diseases in seed beds, ornamentals, tobacco, cotton and vegetables. It can be applied to the soil by irrigating or spreading followed by mechanical mixing into the soil. The chemical can control weed seeds and nematodes. One limitation of this fumigant is that extended periods of time is required post application and prior to planting which cannot be accepted by the growers.

14.3.3 Problems with the Alternatives The other fumigants have narrow range and can be used in many crop systems. They are fungicides and nematicides used in only small scale. There is no complete replacement for MBr. The process of soil solarization or SSOL can be important in the case non-chemical procedure. SSOL is trapping of solar irradiation by covering wet soil and the covering can involve the help of plastic sheets or transparent polyethylene sheets. This results in excess heats where the pathogens cannot survive and hence the soil will be free of pathogens. It is generally done for 4 to 6 weeks. The quantitative measurements showed that post application of this technique there are two important categories of pathogens. The pathogens in one region can be controlled effectively by this SSOL in one region while in another region it was not controlled. It is based on the cultural and environmental parameters. Application of SSOL for about 2 months has reduced the symptoms caused by bacteria in the greenhouse crops. The gram positive bacteria were reduced by about 65%. The major problem with SSOL is that they are dependent on the climate. Another problem is that the greenhouse requires 2-month treatment without crop. Limited pest control and lowered efficiency in some regions can be the reason why SSOL is not yet used worldwide.

Disinfestation

201

14.4 IMPORTANCE OF SELECTIVE PESTICIDES The success of the biological control agents which prevent pest outbreaks in protected crops has pushed us to install greenhouse industries. This has made us conscious about the importance of the selective pesticides. The activity of a pesticide can be restricted to a small range of the pests. In integrated pest management, a pesticide is studied to augment its effects on targets rather than non-target organisms. The action and toxicity of a pesticide is dependent on the physiological selectivity and the procedures of application. The use of chemical pesticides can have undesired effects on beneficial organisms, which can result in pest outbreaks. In case of tomatoes, multiple applications of carbamate methomyl can control the leafminer infestation. This infestation can be eliminated by the use of beneficial parasitoid complexes. This requires lowering the harmful effects on the natural enemies with the help of biological control agents in IPM methods. Some of the pathogens and pests developed resistance against chemical pesticides that should be taken into consideration to prevent the excess use of pesticides.

14.5 SIDE-EFFECTS Pesticides show primary and secondary effects on predators, pathogens and parasitoids of target pests. The primary effects can be indirect or direct and it is based on their exposure time and biological parameters. The mortality of useful organisms is due to direct contact while application, residues of the pesticide, ingesting contaminated prey, intoxication due to fumigants and soil contamination with disinfectants. The sublethal effects on useful arthropods is that there will be lowered reproduction, shift in sex-ratio, delayed development, egg viability and longevity, predation, parasitization and oviposition as well as behavioral and morphological variations. The secondary effects by pesticides includes killing of the prey or host of a useful organism. They can produce alternative food such as honeydew due to ingestion of contaminated food. Alternatively, the direct stimulation of the pest is also seen such as increase in pyrethroids and increased rate of reproduction in case of Tetranychus urticae. Pesticides can affect biocontrol agents like entomopathogenic fungi by reducing the germination of spores and mycelia growth. The can also lower the viability of the conidia. The infectivity of the juveniles of the nematodes can be affected adversely. The side-effects of these pesticides on natural enemies can differ between taxonomic groups. Theiling and Croft showed

202

Greenhouse Pest Management

that predators become tolerant to pesticides. The tolerance of the natural enemies of aphids decreases across Coccinellids to Hymenoptera: described as Coccinellids > Chrysopids > Syrphids > Hemipters > Hymenoptera. The differences in the susceptibilities have been recorded among taxonomically close species within the same species. The adults of Eretmocerus mundus are less susceptible to cypermethrin, thiodicarb and amitraz than Eretmocerus formosa. Response of various species of the fungi against copper in agar is also different. Paecilomyces farinosus is more tolerant than Vericilium lecanii. If the local strains are exposed repeatedly to chemicals then they encourage the natural enemies to grow tolerance against pesticides. The development stages can influence the natural enemy’s response to the pesticides. The susceptibility of Chysoperla cornea and A. aphidimyz towards pesticides with contact mode of action enhanced from the egg stage to adults. The susceptibility of the pesticide is lower in the case of adults of Coccinells septempunctata. The host bestows parasitoids with varying degrees of protection towards pesticides. The developmental stages, protected stages and unprotected stages can exhibit varying levels of mortality post the same pesticide treatment. Avermectin B has killed about half of E.formosa ;protected with the whitefly scales via direct contact test.

14.6 TESTS Species of microorganisms and arthropods are the natural enemies for various crops. These species have various test methods for varying levels of development. The pesticide screening is dependent on criteria of 3 steps: laboratory, semi-field and field conditions. This program assumes that the pesticides are completely harmless in the lab that is still safe in field and semi-field conditions. There is no inference of harmful effects in the event of an earlier report of its harm of pesticides. Tests are conducted until there is a complete report of zero toxicity. The pesticides are tested at recommended field rate as the commercial fertilizers. The lab methods can evaluate the initial toxicity of the pesticides on protected and susceptible developmental stages of the arthropods; classified as lab-a and b test. The lab-a test is used for detection pesticides that can be harmless to the test organism after the exposure to the dried pesticide on a test surface at a single application. The results of the tests must include the mortality and the reproduction of an organism being tested. The information regarding the time of the effect of a particular pesticide can be given by persistence test. The plant material can be sprayed with the pesticide in question on the plant in greenhouses.

Disinfestation

203

The leaf samples can progress to next step that is almost similar to the lab-a test. The next test can be a semi-field test done on the pesticide residues on the plant and arthropods. The behavioral changes and sublethal effects of more applications of a product can be evaluated as shown in Figure 14.1.

Figure 14.1: sequential procedures (Source: Hassan, 1989).

The lab-a test for parasitoids like E.formosa can be done as a contact test with gall midges and adult wasps to evaluate reproduction and mortality. In case of lab-b test the stages protected in their hosts can be sprayed with the pesticide and the emergence rate can be assessed. The lab-a-test for mites can be a contact test that starts from predatory larvae or some protonymphs. This tests the escaping rate, reproduction per female and mortality rate. Similar testing processes can be used in lab-a test and the emergence of eggs can also be assessed. The lab-b test for O.niger can be almost similar as lab-a-test by using predatory bug adults. Lab-b test for A. aphidimyza can be done with larvae as contact tests on leaves or as persistence tests. The lab tests for Syrphus corolla and C.carnes can follow the same principles. The larvae are tested in contact test in order to evaluate the reproduction and mortality of the test organisms. The persistence can evaluate the duration of the harmful effects of the pesticides and are almost the same for all the test species. Some of the plants were sprayed and grown under the greenhouse conditions at varying time periods. The leaf samples can be collected at frequently intervals. They will be used as test surfaces for lab-a and b tests. There is a reevaluation of reproduction and mortality. The persistence should be considered as a lab test which is extended. The sequential testing for M.anisopliae and B.bassiana can constitute all 3 test levels. In lab tests, the growth of mycelia on agar with pesticides is measured. The viability and production of the conidia is evaluated with the help of a bioassay in order to investigate the virulence. In case of semifield test, the conidia can be mixed with the soil and will be treated with the pesticide under test. Following incubation, the spore per unit of the soil is

204

Greenhouse Pest Management

measured. The Gallieria-bait method is employed to assess the virulence at every stage. The testing of side effects at the juvenile stage of the nematodes can be done with a 2 step scheme. The behavior and viability of the pests is done in vitro in pesticide solutions. The infectivity and mobility can be investigated with the help of bioassay in the soil. The pesticide compatibility with bumble-bees which were used as natural pollinators can be classified into 4 categories in the greenhouses.

14.7 EFFECT OF CHEMICAL PESTICIDES ON USEFUL ORGANISMS Fungicides, acaricides and herbicides can have lesser effects than insecticides. The predatory mites are destroyed by pyrethroids and carbamates. Aphidoletes aphidimyza exhibits the same susceptibility to acaricide and insecticide treatments. In case of coccinellids, there will be high mortality rates by test compounds. The Chrysopids are damaged by acaricides. The predatory bugs are reduced by Ops, carbamates, pyrethroids. The synthetic pyethrin and pyrethroids can harm adults regardless of the test species. In case of tests with the protected stages many pyrethroids can be harmful. Ops are harmful to the stages that are unprotected. They may also harm some of the protected life stages and exhibited higher persistence. The carbamates are harmful in both lab tests; some of them have persistence of less than 3 days. The IGRs and acaricides can be harmless to protected developmental stage and susceptible stages of the parasitoids. The plant extracts, microorganism and soap can be harmless. The fungicides can exhibit broad spectrum and the protective mode was harmful to the parasitoids. Few herbicides were harmful to wasps in their adult stages and not in the developmental stages. Few carbamates can affect entomopathogenic nematodes. The fungicides were proved to be harmless. Herbicides, acaricides and insecticides did not influence the mycelia growth of the fungal species of M.anisopliae, B.bassiana and V.lecanii in lab tests in a greenhouse. Many fungicides were examined where a quarter of the fungicides were proved to be harmless. The effects can be due to the mode of action of fungicides. Sublethal effects were shown in many investigations. The effects of pesticide application includes enhanced tendencies to escape from the surfaces treated, changes in pathogenicity of the entomopathogens, reduction in forage behavior for prey consumption, lowered egg production and prolongation of development. The importance of the repellence of

Disinfestation

205

pesticides for beneficial can be harder to classify. The repellence can influence negatively on the natural enemies by removing them from their prey or host that may be required for the development of population. The beneficial organisms can be protected from hazardous contact with the plant surfaces, which are contaminated. These effects can be undesirable in the case of greenhouses where the arthropods are introduced as biological control agents. The natural enemies cease to be effective as agents of control if the amount of untreated refuges are less. The use of insect growth regulators like teflubenzuron, flufenoxuron, fenoxycard, chlorfluazuron and diflubenzuron can be considered harmful to the beneficial organisms. They interfere with the reproduction process, moulting process and viability of the eggs. The effect of various pesticide formulations on natural enemies can be described using endosulfan; , an emulsifiable concentrate which has exhibited 17% of reduced mortality in P.persimilis than wet formulation in a lab test.

14.8 FACTORS INVOLVED The minimal area in greenhouses and higher plant density can determine the use of the operating spray equipment. In the case of closed structures, there are good ambient conditions for the application of minute particles and usage of the artificial air to enhance the distribution of pesticides and control of pests. Sophisticated chemical control can badly affect the bioagents like arthropods, antagonistic fungi and bumble-bees which are to be considered while selecting the pesticides. The application of the pesticides in closed areas can enhance the risk of breathing air with minute particles of the pesticides. The personal clothing can be hot and uncomfortable which render the workers in the greenhouse unprotected. Many producers use high volume spraying despite of all the harmful effects. Its range reaches greater than 1000 liters per hectare. The high volume spraying can run off to wastage which may be about 70 to 90% of dripping to the ground. If there is low concentration of high volume (HV) applications then there will be reduced risk to the operator. The operators are always contaminated with pesticide and the producers are forced to repeat the high volume sprays at close intervals. The entire area under the greenhouse may get heavily contaminated with the pesticide. This condition can make us to feel hard to use the integrated biological control methods with chemicals. The volume of the spray and the runoff can be lowered by altering the nozzles which can produce minute droplets that won’t

206

Greenhouse Pest Management

coalesce on the target. The alternative for HV spraying is the use of cold or thermal foggers that save labor and time. They are only suited for enclosed greenhouses. The deposition can be enhanced by the process of cold fogging with less persistence. The lesser persistence with the cold foggers can permit the introduction of the natural enemies swiftly post treatment followed by the use of a thermal fogger. The greenhouses are to be treated if the parasitoids are protected inside the host stages which are being infested. The cold fogging can permit the application of biopesticides like Bacillius thuringiensis which was used in the process of cold fogging. The vaporization technique can be used in small areas which are about 100 square meters. The pesticides like sulfur can be arranged in a small heater installed with a wide pipe inside. Post evaporation and sublimation, the pesticide condenses into minute particles of about 2 to 8 micrometers. It is carried by hot air via a pipe. The dispersion and particle settling of this size can be affected by the air circulatory systems inside and they deposit primarily on the upper surface of the leaves and so there will be limited residual effect. Some of the alternatives to the spray treatments are application of drenches and granules and chemigation with the help of drip irrigation into the soil if the systemic pesticides were employed. These treatments can be fused with the pesticide and other lure types such as yellow cards in a method named as “lure and kill method”. The thrips are controlled with a polybutene surface that is fused with thripstick (an insecticide). Specific baits may cause minimal damage to the non-target organisms since the exposure chance is lower. The timing of the treatment with pesticides is important so that we can prevent target of the susceptible life forms of the organism, which is not a target. The chemical pesticides can affect the fungus V.lecanii hence, they are to be applied after some time and not immediately. The alternation of the chemical fungicides with the Trichoderma spp which is a fungal biocontrol agent can be used as tank mix for regulation of foliar pathogens. The selective application can be done by considering the spatial factors and systemic pesticides as seed treatment or granules to preserve the organisms that inhabit a plant. Minimal areas can be treated with the handheld spinning disc sprayers. Repeated applications of a pesticide can cause reduction in the number of the natural enemies without control of the pest which is targeted. Single, good timed application of a pesticide can regulate the pest to certain extent without adversely damaging the natural enemies. This will give us overall control of the greenhouse. The pest can

Disinfestation

207

be kept at below the economic threshold and it can be achieved with the variable use of the methamidophos and oxamyl against L.sativae. The systemic fungicides are harmful to V.lecanii if applied as sprays. This did not affect the pathogenecity of the fungus against Aphis gossypii on the cucumber if applied as a soil drench. Another possibility of the preserving natural enemies is the treatment of the strata selected of the plants. This may be flowers and leaves. The lower part of the canopy must be untreated so that there will be management of enough natural enemy populations. The localized treatments gain wide acceptance if the insects pollinate the crops. The producers release the natural enemies like E.formosa. The application of pyriroxyifen on the surface parts controlled greenhouse whitefy without affecting E.formosa.

14.9 PESTICIDE RESISTANCE AND ANTI-RESISTANCE Pathogens and pests can overcome the toxic effects conferred by pesticides by metabolizing the active ingredients into minimal toxic components or products, altering the target site, lowering the chemical absorption and preventing exposure to the chemical compound. The development of resistance can be a challenge to pesticides. In case of greenhouses, there will be resistant strains of pests and fungi that can appear often. This happens since a greenhouse is a closed system with low chances of mixing or dilution by wild populations form the exterior. The presence of the epidemic conditions can be an important factor for the generation of the resistant populations of the pathogens and pests. The standards conditions existing in the greenhouses can be optimal conditions for the development of pests and pathogens for longer periods. The frequency of the life cycles can be enhanced because of the optimal conditions over prolonged periods. The control demands repeated pesticide applications. This can yield higher selection pressure towards pesticide resistance. The important pathogens which can develop resistance to the fungicides in case of greenhouses are Botyris cinerea, Pseudoperonospora cubensis, Didymella bryoniae, Spharotheca fusca, Puccinia horiana, Uromyces dianthi and Usarium osysporium. The benzimidazole fungicides like thiophanates, carbendazim and benomyl can exhibit higher resistance potential against many pathogens since they possess special mode of action. The resistance cannot be associated with loss of fitness of the pathogen. It occurs in populations of

208

Greenhouse Pest Management

powdery mildew, Fusarium, D.bryoniae and B.cinerea. The alternations and mixtures with multiple site contact fungicides can delay the process of selection prior to the resistance becoming apparent. The main problems of resistance to dicarboximide fungicides like vinclozolin,procymidone and iprodione have surfaced due to extensive or indiscriminate use of fungicides. The isolates can be resistant and can be fit as the sensitive strains if there are no fungicides. It is important to restrict the frequency of dicarboximide treatment to 3 per crop in the case of greenhouses in the presence or absence of resistance. If the pressure due to infection is higher, it is important to mix the fungicides with some protectants like captan, TMTD and chlorothalonil or with some other biocontrol agents. The TMTD can interfere with the natural enemies. The Ergosterol biosynthesis inhibitors or in short EBIs are a group of fungicides which are pyrimidine, imidazole and triazole fungicides that inhibit C14 demethylaton and morpholines. The resistance against these EBIs can develop in the form of the slow shifts in the pathogen population. The powdery mildews can be controlled by EBIs, pyrazophos, hydroxypyrimidines and benzimidazoles for many years. The resistance was noticed in the S.fusca however the alternation of the fungicides was practiced in several countries. It is important to rotate and mix EBI fungicides with the fungicides of other groups along with biocontrol. The failure to control the diseases in greenhouses can be noted with the history of the grey mole epidemics. The resistant isolates can occur in the greenhouses with resistance against EBIs, dicarbosimides, diethofencarb and benzimibazole. Extreme summer conditions may not interfere with the existence of the fungicide resistant isolates. Phenylamide fungicides can inhibit the RNA synthesis to regulate Phycomycetes. P.cubensis was controlled with chlorothalonil and dithiocarbamates, Phenylamide metalaxyl was released and the resistant strains were selected in the 80s. The Metalaxyl resistant strains were more competitive than the wild type strains. The resistance has been seen in Phytophthora spp on tomato and lettuce. Anti-resistance mixtures of metalaxyl along with fungicides were developed to withstand the phenilamide resistance. To reduce the pressure towards the resistance development in pathogen, it is a good practice to expose the pathogen to certain group of fungicides. The frequency of the fungicides with same mode of action can be limited. This is against fungi with several numbers of cycles in a growing season. The application of non-chemical methods can also be used. The acaricide

Disinfestation

209

and insecticide resistance of all greenhouse pests is documented. Along with the genetic and operational factors which can affect the selection of resistant species the biotic reasons like reproduction type, offspring per generation, turn-over have a major impact on the development of resistance. Most of the pests on the crops grown in the greenhouse can encourage resistance selection with respect to the biological parameters. Bemisia tabaci and Bemisia aregentifolii have enhanced resistance against many conventional insecticides as well as juvenile hormone analogs and IGRs. Frankliniella occidentalis developed resistance against many pesticide groups to cause heavy losses in the crops affected. The pesticide resistance can be developed in the natural enemies and have been observed in many taxonomic groups. The variations in occurrence and the pesticide resistance level in parasitoids and predators is dictated by the factors such as differential susceptibility and food limitation. Final note: This chapter discussed the various mechanisms associated with resistance of pathogens to pesticides. This requires a thorough evaluation to design a good IPM in greenhouses.

CHAPTER 15

COMMON PESTS

CONTENTS 15.1 Introduction ................................................................................... 212 15.2 Pink Hibiscus Mealybug ................................................................ 212 15.3 Chilli Thrips ................................................................................... 214 15.4 Leafminer ...................................................................................... 216 15.5 Two-Spotted Spider Mites............................................................... 219 15.6 Fungus Gnats ................................................................................. 221 15.7 Shore Flies ..................................................................................... 223 15.8 Whiteflies ...................................................................................... 224 15.9 Aphids ........................................................................................... 225 15.10 Thrips........................................................................................... 228 15.11 Scales .......................................................................................... 229 15.12 Identification ............................................................................... 231

212

Greenhouse Pest Management

15.1 INTRODUCTION This chapter mainly focuses on the common pests observed in greenhouses. This chapter aims to aid a reader to visually identify signs of damage and how to examine plants in a greenhouse for attacks as well as suitable treatment options. Some of the pests are Pink Hibiscus mealybug, Chilli thrips, Leafminer, Two-spotted Spider Mite, Fungus Gnats/Shore flies, Whiteflies, Aphids, Thrips and Scales.

15.2 PINK HIBISCUS MEALYBUG

Figure 15.1: Pink Hibiscus mealybug. Source: https://www.hort.vt.edu

This pest is distributed in the tropics, which includes Asia, Oceania, Australia, the Middle East and Africa. It is considered as a serious pest especially in the Caribbean. It attacks several hosts which have much economic importance. It has disturbed commerce of the Caribbean countries.

Common Pests

213

Figure 15.2: Pink Hibiscus mealybug-Damage. Source: https://www.uvm.edu

The mealybugs can feed on sap of the plant. Minimal infestations can weaken host plant and in case of high populations the host may die. The leaves of the host plant can appear chlorotic that eventually get dried and detache from the stem. The pest can produce honey dew. Black sooty mold develops on the surface of the leaves. This pest has a vast host range. They are carried by the imported plant materials especially from the tropical areas. The mouth parts of this pest are of piercing and/or sucking type. They have soft bodied scales. They can produce white cottony and waxy covering material that covers their bodies. They can also have long , waxy and filamentous projections. The eggs are laid below this waxy material. The individuals can move on the plant tosearch for the best place to settle. They can insert the mouth parts and feed all their life with little movement. In case of greenhouses, we can observe six generations per year. The ants which eat honeydew can carry mealybugs and help spreading of this pest. One must search for minute cottony blotches. Large sized colonies can be observed around the plant nodes. With the help of a wire piece or needle we can peel back the cotton mass to observe the mealybug. They can infect

214

Greenhouse Pest Management

roots. Early detection can be important. They can be least controlled by insecticides. Biological control can be a good choice.

15.3 CHILLI THRIPS

Figure 15.3: Chilli thrips.

Source: https://www.hort.vt.edu They are also called as Scirtothrips dorsalis. They are found mainly in Florida and Texas.

Figure 15.4: Deformed pepper fruit. Source: https://www.hort.vt.edu

Common Pests

215

Figure 15.5: Feeding scars. Source: https://www.hort.vt.edu

General symptoms during the pest infestation include scars, distorted or stunted flowers and leaves. We can observe white and sunken patches on the flower petals or upper surface of the leaf. We can observe black droplets. The producers must also verify if there are any viral infections as the thrips can carry virus. They primarily attack ornamental plants. They are ivy geranium, impatiens, cineraria, potulaca, African violet, cyclamen and chrysanthemum. They have modified sucking and piercing type of mouth parts. The adults are yellow and brown. They are fast moving, slender and tiny insects. They measure about a size of flea. They get protection from the leaf crevices or may hide deep in the flower so that we find it hard to observe with hand lens. In case of high temperatures, they can exhibit high population rise and we can see many generations in a year. The eggs will be laid in the plant tissue and pesticides cannot act on them. The immature and adults can be observed in the flowers. They can be observed along the leaf veins or in some cases in the leaf crevices. The thrips can be caught on sticky cards.

216

Greenhouse Pest Management

15.4 LEAFMINER

Figure 15.6: Leafminer. Source: https://www.hort.vt.edu

Figure 15.7: Leafminer – Adult. Source: https://www.hort.vt.edu

Common Pests

Figure 15.8: Leafminer – Larva. Source: https://www.uvm.edu

Figure 15.9: Leafminer – Larva. Source: https://www.uvm.edu

217

218

Greenhouse Pest Management

Figure 15.10: Leafminer – Adult. Source: https://www.uvm.edu

Figure 15.11: Leafminer – Tunneling damage. Source: https://www.uvm.edu

The eggs are generally laid in the leaves and also in punctures which are called as stipples. The eggs can hatch in 3 days. The larvae can generate white tunnels on the leaf. The female leafminers can punch in leaves to consume on the plant sap. The damage can be on the leaves of Zinnia, snapdragon, petunia, marigold, gypsophila, gerbera, dahlia, chrysanthemum, calendula, aster and ageratum. They have chewing type of mouth parts. Two species are dominant in New England. It is hard to differentiate these two species. Black and yellow marking may be present. The larvae can tunnel in the leaf tissue and they make a semi-circular opening before dropping into the

Common Pests

219

soil for pupation. In case of warm conditions, they can mature in 6 days. The pupae can live for about 90 days. It is better to remove infested leaves. All the weeds and plant debris must be removed. Crop rotation, removal of chrysanthemum are good options to address this pest. The soils can be covered with plastic mulch.

15.5 TWO-SPOTTED SPIDER MITES

Figure 15.12: Two spotted spider mite. Source: https://www.hort.vt.edu

Figure 15.13: Two spotted spider mite-Damage. Source: https://www.hort.vt.edu

220

Greenhouse Pest Management

Figure 15.14: Two spotted spider mite-Stippling. Source: https://www.uvm.edu

Figure 15.15: Two spotted spider mite-Webbing. Source: https://www.uvm.edu

Figure 15.16: Two spotted spider mite-Blotchy appearance. Source: https://www.uvm.edu

Common Pests

221

The damage caused is visualized as fine webbing underside the leaf and silver sheen. There will be no fecal deposits. The damage can be observed as stippling or yellow dots on the leaves. In case of maximal infestation, the leaves may be covered with webbing. Eventually they turn yellow and can drop. The damage can lower the quality of the crop in ornamental plants such as chrysanthemum. The mouthparts are of sucking and piercing type. The mites can lay about 120 eggs in 3 weeks. They are translucent and rounded. The eggs develop into 6 legged immature and later develop into 8 legged adults. In summer season, they turn red. The initial infestations occur underside the leaf. Mottled leaf can be a characteristic feature of this infection. The damage is more on the young leaves. Sanitation is crucial to control this infestation. The use of predatory mites can be a good choice. Miticides are also used to control mites.

15.6 FUNGUS GNATS

Figure 15.17: Fungus Gnats. Source: https://www.hort.vt.edu

Figure 15.18: Fungus Gnats- Damaged plant. Source: https://www.uvm.edu

222

Greenhouse Pest Management

Figure 15.19: Fungus Gnats- Tunneling in the stem. Source: https://www.uvm.edu

This larva can feed on root hairs. They can tunnel into the stems. The tunnels in the stem can be entry points for plant pathogens such as Verticillium, Fusarium and Pythium. The adult fungus gnats can spread spores of these pathogen on their bodies to thus function as vectors. The feeding on root and tunneling can damage nutrient and water uptake that results in wilted yellow plants. The pest attacks poinsettia and geranium. The mouth parts are of chewing type. The adults cannot damage but they can serve as vectors for spreading fungal diseases. The larvae can feed on roots and stem. They can feed on rotting vegetation under the soil surface. Organic matter rich soils, wet conditions and less light can favor the increase in population. The adults are considered weak. They resemble mosquitoes with long antennae and legs with dark bodies. Y- Patterned veins in the wings can be observed with hand lens. The life cycle can be completed in 27 days that depends on the temperature. The adults live on the soil surface of plants and pots. In case of disturbance, they can fly around. The larvae can be observed in the plant stems or under the soil surface. Sticky cards are used to monitor adults and potato wedges can be employed to monitor larvae. The control of this pest can be by reducing organic matter and monitoring their populations. Biological controls, Insecticides and bio pesticides can be effective.

Common Pests

223

15.7 SHORE FLIES

Figure 15.20: Shore flies- Larva. Source: https://www.uvm.edu

Figure 15.21: Shore flies- Adults. Source: https://www.uvm.edu

They cause serious damage to plants and are capable of transmitting fungal diseases in a greenhouse. The larvae can feed on algae and dead plant matter. They are present in the damp areas where the growth of algae is common. They have mouth parts which are of chewing type. The Scatella shore flies are minute and the black flies have red eyes with gray wings. They can be captured on a sticky card for monitoring. Leaks must be eliminated and floors must be treated so that the algae can be eliminated.

224

Greenhouse Pest Management

15.8 WHITEFLIES

Figure 15.22: White flies- Adults. Source: https://www.hort.vt.edu

Figure 15.23: White flies- Pupa (Silver leaf). Source: https://www.hort.vt.edu

Figure 15.24: White flies- Pupa (Greenhouse). Source: https://www.hort.vt.edu

Common Pests

225

The leaves turn yellow and they can drop off eventually. In case of heavy infestation, there will be reduced growth and wilting of plants. The veins alone can remain green. They can secrete honeydew and hence there will be shiny residue on the leaf. The sooty mold can grow on the surface of the leaf. Some of the whiteflies can spread viruses. This pest can attack bedding plants, verbena, gerbera, geranium, lantana, hibiscus and Poinsettia. The mouth parts are of sucking and piercing type. The adults are longer with white wings. The circular eggs are minute and they are laid underside leaf. The immature eggs can be oval and translucentof yellow or white color. Early immature stages are motile whereas other stages are non-motile. The shape of the pupae can be important in identification of the species. Most common species are silver leaf and greenhouse whitefly. The immature organisms are observed underside leaf and the adults can fly around. White powdery material can help diagnose the problem. Biorational insecticides, biological control and accurate species identification are important to control this pest.

15.9 APHIDS

Figure 15.25: Aphids. Source: https://www.hort.vt.edu

226

Greenhouse Pest Management

Figure 15.26: Aphids-Tail pipes. Source: https://www.hort.vt.edu

Figure 15.27: Aphids-Rose buds. Source: https://www.hort.vt.edu

Figure 15.28: Aphids-Underside of leaf. Source: https://www.hort.vt.edu

Common Pests

227

Figure 15.29: Aphids-Immature. Source: https://www.hort.vt.edu

Figure 15.30: Aphids- Sooty mold. Source: https://www.hort.vt.edu

These insects feed on sap. The infested plants can exhibit stunted and distorted plant tissues. The young flowers and foliage are malformed. Some of the species can spread viruses. The aphids excrete honeydew substance that is sweet and stickyto give a shiny appearance of the leaf. The blacky sooty mold generates on honeydew on the surface of the plant. The pest contains mouthparts which are of sucking and piercing type. They have long

228

Greenhouse Pest Management

oval bodies which are soft. At the end of the tail, there are two slender tubes which are called as cornicles. The immature and adults can feed together. Mostly they won’t lay eggs and are capable of giving birth to young ones. The life cycle is rapid with quick reproduction cycles. They cannot be detected with color alone. Species identification and treatment of aphids can be important. Biorational insecticides can be more effective.

15.10 THRIPS

Figure 15.31: Thrips. Source: https://www.hort.vt.edu

Figure 15.32: Thrips-Damage(Peony). Source: https://www.hort.vt.edu

Common Pests

Figure 15.33 Thrips-Damage Source: https://www.hort.vt.edu

15.11 SCALES

Figure 15.34: Scales-Hemispherical. Source: https://www.hort.vt.edu

229

230

Greenhouse Pest Management

Figure 15.35: Scales-Florida red scale. Source: https://www.hort.vt.edu

Figure 15.36: Scales-Cactus. Source: https://www.hort.vt.edu

There are soft scales and armored scales. The soft scales can be classified into hemispherical scale and Brown soft scale. The armored scales can be classified into Florida red scale, Cactus scale and Boisduval scale. They

Common Pests

231

can be controlled with physical removal and isolation of plants. Insecticidal soaps and horticultural oils can also be used.

15.12 IDENTIFICATION

Figure 15.37: Scouting-Yellow sticky cards. Source: http://ipm.uconn.edu

Figure 15.38: Scouting-Pests on Yellow sticky cards.

Source: http://ipm.uconn.edu

232

Greenhouse Pest Management

The process of scouting uses yellow sticky cards to trap whiteflies, fungus gnats, winged aphids, leafminers and shoreflies.

Figure 15.39: Scouting-Used in retail greenhouses. Source: http://ipm.uconn.edu

Figure 15.40: Magnification. Source: http://ipm.uconn.edu

Common Pests

233

It is a good practice to use 10X to 20X handle lens to identify the insects trapped on sticky cards.

Figure 15.41: Vertical placement of sticky cards. Source: http://ipm.uconn.edu

Figure 15.42: Horizontal placements of sticky cards. Source: http://ipm.uconn.edu

234

Greenhouse Pest Management

Figure 15.43: Winged adult aphid on sticky cards. Source: http://ipm.uconn.edu

Figure 15.44: Thrips on sticky cards.

Source: http://ipm.uconn.edu

Figure 15.45: Fungus gnat Vs Midges Vs Aphid on sticky cards.

Source: http://ipm.uconn.edu

Common Pests

Figure 15.46: Fungus gnat Vs whiteflies on sticky cards.

Source: http://ipm.uconn.edu

Figure 15.47: Adult Fungus gnat on sticky cards.

Source: http://ipm.uconn.edu

Figure 15.48: Fungus gnat on potato slices. Source: http://ipm.uconn.edu

235

236

Greenhouse Pest Management

Figure 15.49: Fungus gnat and Shorefly. Source: http://ipm.uconn.edu

Figure 15.50: Shoreflies on Algae. Source: http://ipm.uconn.edu

Figure 15.51: Shorefly-Adult. Source: http://ipm.uconn.edu

Common Pests

Figure 15.52: Leafminer-Adult. Source: http://ipm.uconn.edu

Figure 15.53: Leafminer-mines. Source: http://ipm.uconn.edu

Figure 15.54: Shoreflies-fecal dropping. Source: http://ipm.uconn.edu

237

238

Greenhouse Pest Management

Figure 15.55: Leafhopper. Source: http://ipm.uconn.edu

Figure 15.56: Leafhopper-Adult. Source: http://ipm.uconn.edu

Figure 15.57: Thrips-Adult. Source: http://ipm.uconn.edu

Common Pests

Figure 15.58: Whiteflies. Source: http://ipm.uconn.edu

Figure 15.59: Whiteflies-Adult. Source: http://ipm.uconn.edu

Figure 15.60: Banded winged Whitefly-Adult. Source: http://ipm.uconn.edu

239

240

Greenhouse Pest Management

Figure 15.61: Greenhouse Whitefly-Pupal stage. Source: http://ipm.uconn.edu

Figure 15.62: Sweet potato Whitefly-Pupal stage. Source: http://ipm.uconn.edu

Figure 15.63: Parasitic wasp. Source: http://ipm.uconn.edu

Common Pests

Figure 15.64: Encarsia formosa-Quality control. Source: http://ipm.uconn.edu

Figure 15.65: Encarsia formosa-Adult. Source: http://ipm.uconn.edu

241

242

Greenhouse Pest Management

Figure 15.66: Eretmocerous- Quality control. Source: http://ipm.uconn.edu

Figure 15.67: Eretmocerous Vs Encarsia- Quality control. Source: http://ipm.uconn.edu

Figure 15.68: Eretmocerous Vs Thrips- Quality control. Source: http://ipm.uconn.edu

Common Pests

Figure 15.69: Shorefly parasitoid. Source: http://www.omafra.gov.on.ca/english/crops/facts/06-079.htm

Figure 15.70: Fungus Gnat parasitoid. Source: http://ipm.uconn.edu

Figure 15.71: Hunter flies. Source: http://ipm.uconn.edu

243

244

Greenhouse Pest Management

Figure 15.72: Hunter flies-Adult. Source: http://ipm.uconn.edu

Figure 15.73: Hunter flies-Shiny wings without spots. Source: http://ipm.uconn.edu

Figure 15.74: Shoreflies Vs Hunter flies. Source: http://www.omafra.gov.on.ca/english/crops/facts/06-079.htm

Common Pests

Figure 15.75: Hover flies. Source: http://www.omafra.gov.on.ca/english/crops/facts/06-079.htm

Figure 15.76: Fungus gnat Vs Midge. Source: http://ipm.uconn.edu

Figure 15.77: Midge-Adults. Source: http://ipm.uconn.edu

245

246

Greenhouse Pest Management

Figure 15.78: Moth. Source: http://www.ces.ncsu.edu/depts/ent/notes/Urban/drainfly.htm

Figure 15.79: Shorefly Vs Mothflies. Source: http://ipm.uconn.edu

During identification, we need to look for a distinct Y-shaped vein at the tip of the wings of an adult Fungus Gnat. Potato chunks or slices are used to monitor the larvae of the fungus gnats. In case of shoreflies, there will be 3 to 5 pale spots on the grayish wings. We can observe a short bristle like antennae as well as long legs. They have a stout body and they are about the size of the fruit flies. The adult leafminers are minute and robust flies. They have a yellow patch which is an important characteristic feature. They possess short antennae and two wings which are transparent. They have a cannon shaped structure at the abdomen that is employed to puncture leaves and also lay eggs. It is better to look for yellow color and plant damages to identify. The leafhoppers are slender insects. They have short bristle like antennae. The wings are held like a roof over the abdomen. They are wedge shaped and some tapering is seen. The antennae are not visible. The color varies and it is based on the species. The thrips are small insects and they can be observed on the cards. They look like narrow and cigar shaped. It is better to look for red eyes and short antennae. We can also observe fringed wings.

Common Pests

247

They have hairs on the end so that they are distinct from peat moss. While identifying whiteflies, we need to look for whitish bloom that can disappear in a few days. The whiteflies can turn orange when they are on the sticky material present on the trap. They are larger than thrips. The banded winged whiteflies are almost same as greenhouse whiteflies. We need to observe two grayish bands. This can form a Zig-zag design across each wing. They enter the greenhouses from weeds growing outside in the fall. The parasitic wasps can be attracted to yellow sticky cards. Some of the beneficial files are hover files and hunter flies. The common parasitic wasps are Hymenoptera species. They can be slender or stout. They have longer and elbowed antennae. The bodies are pointed toward the rear. They can have clear wings with angular vein in front of forewing. Encarsia formosa is used to regulate whiteflies in the greenhouses. They are small with black head and thorax. Yellow abdomen is present. They look like a tiny black dot on yellow card. The Eretmocerus sp are also available as parasitic wasp. It can be used against whiteflies such as sweet potato whiteflies. They appear as yellow or straw colored. They have elbowed antennae. Synacra pauperi are natural parasite of fungus gnats. The size of an adult can be same as that of fungus gnats. We need to look for narrowing between thorax and head. The narrowing is also observed between abdomen and thorax. The abdomen can taper to a sharp tip. The antennae are elbowed and beaded. They can be observed in the unsprayed greenhouses. The hunter flies belongs to house fly family but are smaller. The males appear light gray than females. The wings are uniform and clear. They feed on fungus gnats, leafmining flies and shoreflies. The hover flies have yellow color and they have visible lack markings. They have only one pair of wings. They have shorter antennae. The adults can feed on the nectar and pollen. The larvae feed on aphids and insects. Some of the other insects that are not pests for plant but are found on the cards are midges and moth flies. The midges are minute and delicate insects. They are same as mosquitoes. They have narrow and elongated body. The males are feathery and they possess plumose antennae. The moth or drain flies are small, fuzzy and dark insects. Their body is covered with hairs. The wings are held like a roof over the body. They have large broad wings. The wings are fringed and have a hair like appearance. The antennae are beaded.

CHAPTER 16

COMMON GREENHOUSE CROPS AND PEST MANAGEMENT

CONTENTS 16.1 Introduction ................................................................................... 250 16.2 Major Pests .................................................................................... 250 16.3 IPM................................................................................................ 251 16.4 Cucurbits ....................................................................................... 253 16.5 Strawberries And Greenhouses ...................................................... 257

250

Greenhouse Pest Management

16.1 INTRODUCTION An example: Integrated pest management in greenhouse tomato or Lycopersicon esculentum. Crops are firmly identified with climatic territories. In cool regions like northern Europe, tomatoes are cultivated in glasshouses, though in the hotter territories like Mediterranean basin and Middle East, plastic houses are preferred. In the EU most of the tomato production is about 78% is in the hotter territories (Aldanondo, 1995). Over the recent thirty years, ensured development of tomato has expanded extraordinarily in the warm districts. Presently, yields of in excess of 200 t/ha can be gathered in numerous Mediterranean countries (van Alebeek and van Lenteren, 1990). Be that as it may, the heightening of secured tomato generation has made ideal conditions for some pests. For instance, a few pathogens like Leveillula taurica (Lév.) G. Arnaud, Botrytis cinerea Pers.:Fr., Clavibacter michiganensis (Smith) Davis et al. ssp. michiganensis (Smith) Davis et al. [= Corynebacterium michiganense (Smith) Jensen ssp. michiganense (Smith) Jensen], Meloidogyne spp.} were simple to control in the early years, but have wreaked more harm as the development turned out to be more extraordinary (van Alebeek and van Lenteren, 1990; Besri, 1991a).

16.2 MAJOR PESTS The most destructive pests on tomato crops are polyphagous. Their relative significance fluctuates with the climatological territory and sort of greenhouse. The crucial pests on this harvest are whiteflies and, to a lesser degree, leafminers. aphids, lepidopteran hatchlings and parasites may cause extreme monetary loss, yet their rate is variable. Exposed to the cold regions and in part of the warm zone, Trialeurodes evaporariorum (Westwood) is the whitefly species on greenhouse tomato (Onillon, 1990; van Lenteren et al., 1992). Trialeurodes vaporariorum and Bemisia tabaci (Gennadius) exist together in the change subarea (Arnó and Gabarra, 1994) and just B. tabaci causes harm in the hotter subarea (Traboulsi, 1994; Gerling, 1996). Diverse Bemisia species as well as B. tabaci biotypes coincide in a few sections of the world (Markham et al., 1996). The infection dispersion, occurrence and severity fluctuate starting with one area then onto the next, as indicated by numerous variables, for example, the cultivars, the climatic conditions, the type of greenhouse, the cultural practices and the control strategies utilized (van Alebeek and van Lenteren, 1990). Phytophthora infestans (Mont.) de Bary is more serious in

Common Greenhouse Crops and Pest Management

251

polyethylene houses than in glasshouses, yet the inverse is valid on account of Fulvia fulva (Cooke) Cif. (= Cladosporium fulvum Cooke) (Garibaldi and Corte, 1987). This pathogen is more successive and more serious in the Northern and Eastern Mediterranean nations than in the southern ones. Wide open to the cold elements zones Verticillium wilt is because of Verticillium albo-atrum and in the warm zones to Verticillium dahliae Kleb. (Jones et al., 1991). Pyrenochaeta lycopersici R. Scheneider and Gerlach, B. cinerea and Rhizoctonia solani Kühn are extreme in all cropping regions, however their severity shifts with the area and the cultural practices. Infections, nematodes and bacterial diseases cause problems in case of Mediterranean areas (van Lenteren, 1987; van Alebeek and van Lenteren, 1990).

16.3 IPM Sanitation is a critical segment of IPM. This control strategy incorporates all activities intended to wipe out or diminish the inoculum in a plant or plot, thus regulate the spread of the pests (Agrios, 1988). Hence, furrowing under or evacuation and appropriate transfer of infested plant that may harbor the pest diminishes the measure of inoculum. Washing the equipment before development starting with one plot then onto the next may likewise maintain a strategic distance from the spread of pathogens in the soil. Since weeds can be infested by indistinguishable pest from the essential host, it is imperative to control their development (Besri, 1991a) and kill weeds from the exteriors of greenhouses no less than about fourteen days before planting. This can postpones whitefly infestation in warm territories (Alomar et al., 1989). Numerous tomato pathogens, for example, Alternaria solani Sorauer, Didymella lycopersici Kleb. [teleomorph of Phoma lycopersici Cooke (= Diplodina lycopersici Hollós)], Fusarium oxysporum Schlechtend.:Fr. f. sp. lycopersici (Sacc.) W.C. Snyder and H.N. Hans., C. michiganensis ssp. michiganensis, Pseudomonas syringae van Hall pv. tomato (Okabe) furthermore, ToMV are transmitted by seeds (Jones et al., 1991). The utilization of pathogen free seeds should, consequently, be a vital segment of any tomato IPM program (Besri, 1978; van Alebeek and van Lenteren, 1990). Some cultural practices help tomato plants and therefore enhance their pest resistance. Along these lines, fertilization, waste, appropriate spacing of plants, weed control, and so forth enhance the plants’ development and may have an immediate or backhanded impact on the control of a specific pest (Agrios, 1988; Besri, 1991a). Salinity of soil and water can enhance

252

Greenhouse Pest Management

the susceptibility of tomato plants to numerous diseases and especially to Verticillium wilts and Fusarium. Resistant varieties are vulnerable at the point when the irrigation water has a high level of salt. Decreasing the salinity of water substance by blending non-salty water from dams with salty water pumped from wells diminishes the occurrence and severity of these two pathogens (Besri, 1981). In the common greenhouses in the Mediterranean and Middle East, anticipation of airborne pathogens, for example, A. solani, B. cinerea, L. taurica and P. infestans by keeping greenhouse vents shut isn’t constantly conceivable, on the grounds that this may lack ventilation and a resultant increment in moistness advances diseases (van Alebeek and van Lenteren, 1990; Nicot and Allex, 1991; Nicot and Baille, 1996). At the point when B. tabaci and TYLCV are available in the region, screening the greenhouse is an imperative IPM process. Tomato plants are pruned to expel axillary buds and leaves. Plant pruning makes a drier microclimate in the lower plant, yet in addition gives various purposes of section to numerous pathogens, for example, D. lycopersici and B. cinerea.

Figure 16.1: Flow diagram. Source: Miller, S.A., Lewis Ivey, M.L., Baysal-Gurel, F. and Xiulan Xu (2015). A systems approach to tomato disease management. Acta Hortic. 1069, 167-172

Pruning wounds on tomato plants are less inclined to wind up tainted by these pathogens if the leaves are sliced near the stem than if a part of petiole is left on the stem (Besri and Diatta, 1992). In any case, some common adversaries, as parasitoids of whitefly, are created on the old leaves. For this situation, pruning too soon ought to be evaded and pruned leaves to be kept

Common Greenhouse Crops and Pest Management

253

in the greenhouse until the parasitoids have developed. Good crop rotation isn’t possible in tomato development and soil disinfestation might be costly and unfriendly to environment like methyl bromide, MBr. Soilless culture is a system initially created to decrease the seriousness of soilborne pathogens (Zinnen, 1988; Braun and Supkoff, 1994).

Figure 16.2: Greenhouse grown tomatoes.

Source: https://www.newsgram.com

16.4 CUCURBITS Cucumber crops are developed in many regions of the world, particularly in Northern Europe, the Mediterranean basin, North Africa, Canada and Japan. As the plant reacts to warm temperatures and high humidities, development in glasshouses or plastic secured structures is generally practiced. Air humidity in a greenhouse might be imperfect on winter evenings in light of the extraordinary warming required, and on summer days due to solid sunlight based light. Development is hence especially effective in placid atmospheres, where it is less demanding to keep up conditions ideal for the yield: temperatures somewhere in the range of 16 and 30°C and air humidity around 80%. Such conditions permit an all year generation of top notch natural products. In numerous countries, hydroponic cropping has turned out to be typical in light of the expanded yields achievable. Yields of somewhere in the range of 600 and 700 t/ha are typical for hydroponic harvests in warmed glasshouses, and with artificial light yields more than 1000 t/ha are expected. The following figures show aspects of cucumber culture and few pests that target these plants:

254

Greenhouse Pest Management

Figure 16.3: Greenhouse grown cucumbers. Source: https://www.123rf.com

Figure 16.4: Infection due to spider mite. Source: https://www.123rf.com

Common Greenhouse Crops and Pest Management

Figure 16.5: Downy mildew.

Source: https://www.ipmimages.org

Figure 16.6: Grey mould. Source: https://organicgardeningnewsandinfo.wordpress.com

255

256

Greenhouse Pest Management

Figure 16.7: Gummy stem blight. Source: http://www.omafra.gov.on.ca

Figure 16.8: Pythium root and stem base rot. Source: https://www.alamy.com

Figure 16.9: Cucumber Mosaic Virus. Source: https://luv2garden.com

Common Greenhouse Crops and Pest Management

257

Figure 16.10: Cucumber Mosaic Virus. Source: https://www.pestcontrolnorthbrisbane.com.au

16.5 STRAWBERRIES AND GREENHOUSES Strawberries are cultivated both in open fields and in greenhouses. The greenhouse grown strawberries are done in for example, northern Europe while outside development is prevalent in hotter regions, for example, California and Florida. In the Mediterranean regions, development under plastic is common, despite the fact that its frequency changes among countries.

Figure 16.11: Lepidopteran pests of strawberries. Source: https://ipmworld.umn.edu

Strawberry planting and organic product gathering is done in in Europe more than two cropping seasons, winter and summer, individually. In single

258

Greenhouse Pest Management

cropping seasons, transplants for crop fields, beginning from disease free material, are proliferated from mother plants in greenhouses during the midyear months. Winter plantings from mid to pre-fall prove to be fruitful amid the winter and spring months. The following figures show few pests that target strawberries:

Figure 16.12: Aphid pests of strawberries. Source: http://ucanr.edu

Figure 16.13: Root Weevils pests of strawberries. Source: http://oregonstate.edu

In Europe however, summer crop is overwhelming: in the Mediterranean, production is for the most part intended for a solitary season while in central Europe a semiannual season might be arranged, yet the utilization of this production method has been altogether diminished in the previous years. IPM depends on an improvement of production with insignificant utilization of synthetic compounds, keeping in mind the end goal to diminish risks to people, animals, and plants.

REFERENCES

1.

2.

3.

4. 5.

6.

7.

8.

Aramburu, J., Riudavets, J., Arnó, J., Laviña, A. and Moriones, E. (1997) The proportion of viruliferous individuals in field populations of Frankliniella occidentals: Implications for tomato spotted wilt virus epidemics in tomato, European J. of Plant Pathology 103, 623–629. Aranda, M.A., Fraile, A., Dopazo, J., Malpica, J.M. and García-Arenal, F. (1997) Contribution of mutation and RNA recombination to the evolution of a plant pathogenic RNA, J. of Molecular Evolution 44, 81– 88. Baker, K.F. and Linderman, R.G. (1979) Unique features of the pathology of ornamental plants, Annual Review Phytopathology 17, 253–277. Bakker, J.C. (1995) Greenhouse Climate Control: An Integrated Approach, Wageningen Press, Wageningen. Bates, M.L. and Stanghellini, M.E. (1984) Root rot of hydroponically grown spinach caused by Pythium aphanidermatum and P. dissotocum, Plant Disease 68, 989–991. Brunt, A.A. (1986) Tomato mosaic virus, in M.H.V. van Regenmortel and H. Fraenkel-Conrat (eds.), The Plant Viruses. Vol. II: The Rodshaped Plant Viruses, Plenum Press, New York, pp. 180–204. Brunt, A.A., Crabtree, K., Dallwitz, M.J., Gibbs, A.J. and Watson, L. (1996) Viruses of Plants. Descriptions and Lists from the VIDE Database. CAB International, Wallingford. Cabello, T. and Cañero, R. (1994) Technical efficiency of plant protection in Spanish greenhouses, Crop Protection 13, 153–159.

260

9. 10.

11. 12.

13.

14.

15. 16.

17.

18.

19. 20.

Greenhouse Pest Management

Carrai, C. (1993) Marciume radicale su lattuga alleviate in implant NFT, Colture Protette 22(6), 77–81. Castilla, N. (1994) Greenhouses in the Mediterranean area: Technological level and strategic management, Acta Horticulturae 361, 44–56. Campbell, R.N. (1971) Squash Mosaic Virus, CMI/AAB Descriptions of Plant Viruses No. 43, CMI, Kew. Céiix, A., López-Sesé, A., Almarza, N., Gómez-Guillamón, M.L. and Rodríguez-Cerezo, E. (1996) Characterization of cucurbit yellow stunting disorder virus, a Bemisia tabaci-transmitted closterovirus, Phytopathology 86, 1370–1376. Coffin, R.S. and Coutts, R.H.A. (1993) The closteroviruses, capilloviruses and other similar viruses: A short review, J. of General Virology 74, 1475–1483. Cohen, S. and Antignus, Y. (1994) Tomato yellow leaf curl virus, a whitefly-borne geminivirus. Advances in Disease Vector Research 10, 259–288. Couteaudier, Y., Alabouvette, C. and Soulas, M.L. (1985) Nécrose du collet et pourriture des racines de tomate, Revue Horticole 254, 39–42. Dairymple, D.G. (1973) Controlled Environment Agriculture: A Global Review of Greenhouse Food Production, Foreign Agricultural Economic Report No. 89, Economic Research Service, USDA, Washington, DC. Elad, Y. (1997) Effect of filtration of solar light on the production of conidia by field isolates of Botrytis cinerea and on several diseases of greenhouse-grown vegetables, Crop Protection 16, 635–642. Elad, Y. and Kirshner, B. (1993) Survival in the phylloplane of an introduced biocontrol agent (harzianum) and populations of the plant pathogen Botrytis cinerea as modified by abiotic conditions, Phytoparasitica 21, 303–313. Gonsalves, D. and Gamsey, S.M. (1989) Cross-protection techniques for control of plant virus diseases in the Tropics, Plant Disease 73, 592–597. Grogan, R.G. (1980) Control of lettuce mosaic with virus-free seed. Plant Disease 64, 446–449. Johansen, E., Edwards, M.C. and Hampton, R.O. (1994) Seed transmission of viruses: Current perspectives, Annual Review of Phytopathology 32, 363–386.

References

261

21. Garibaldi, A., Gullino, M.L. and Minuto, G. (1997) Diseases of basil and their control. Plant Disease 81, 124–131. 22. Garibaldi, A. and Tamietti, G. (1984) Attempts to use soil solarization in closed glass houses in northern Italy for controlling corky root of tomato, Acta Horticulturae 152, 237–243. 23. Greenberger, A., Yogev, A. and Katan, J. (1987) Induced suppressiveness in solarized soils, Phytopathology 77, 1663–1667. 24. Grinstein, A. and Ausher, R. (1991) The utilization of soil solarization in Israel, in J. Katan and J.E. DeVay (eds.). Soil Solarization, CRC Publications, Boca Raton, Fla., pp. 193–204. 25. Grinstein, A. and Hetzroni, A. (1991) The technology of soil solarization, in J. Katan and J.E DeVay (eds.) Soil Solarization, CRC Publications, Boca Raton, Fla., pp. 159–170. 26. Grinstein, A., Katan, J., Abdul-Razik, A., Zeidan, O. and Elad, Y. (1979) Control of Sclerotium rolfsii and weeds in peanuts by solar healing of the soil. Plant Disease Reporter 63, 991–994. 27. Grinstein, A., Kritzman, G., Hetzroni, A., Gamliel, A., Mor, M. and Katan, J. (1995) The border effect of soil solarization. Crop Protection 14, 315–320. 28. Hilderbrand, D.M. (1985) Soil solar heating for control of damping-off fungi and weeds at the Colorado State Forest Service Nursery, Tree Planters’ Notes 36, 28–34. 29. Kaewmang, W., Sivasithamparam, K. and Hardy, G.E. (1989) Use of soil solarization to control root rots in gerberas (Gerbera jamesonii), Biology and Fertility of Soils 8, 38–47. 30. Katan, J., Greenberger, A., Alon, H. and Grinstein, A. (1976) Solar heating by polyethylene mulching for control of diseases caused by soilbome pathogens. Phytopathology 66, 683–688 31. Katan, J., Grinstein. A., Greenberger, A., Yarden, O. and DeVay, J.E. (1987) First decade (1976–1986) of soil solarization (solar heating) – A chronological bibliography, Phytoparasitica 15, 229–255. 32. Klein, L. (1996) Methyl bromide as a soil fumigant, in C.H. Bell. N. Price and B. Chakrabarti (eds.), The Methyl Bromide Issue, John Wiley and Sons Ltd, Chichester, pp. 191–235. 33. Kodama, T. and Fukui, T. (1982) Solar heating in closed plastic house for control of soilbome diseases. V. Application for control of Fusarium wilt of strawberry. Annals of the Phytopathological Society of Japan

262

34.

35. 36.

37. 38.

39.

40. 41.

42. 43.

44.

45. 46.

Greenhouse Pest Management

48, 570–577. Kodama, T., Fukui, T. and Matsumoto, Y. (1980) Soil sterilization by solar heating against soil-borne diseases in a closed vinyl house. III. Influence of the treatment on the population level of soil microfiora and the behaviour of strawberry yellows pathogen, Fusarium oxysporum f.sp. fragariae, Bulletin of the Nara Agricultural Experiment Station 11, 41–52. Kritzman, G. and Ben-Yephet, Y. (1990) Disease exchange in onions as influenced by metham-sodium, Hassadeh 1, 26–29. Malathrakis, N.E., Kapetanakis, G.E. and Linardakis, D.C. (1983) Brown root rot of tomato and its control in Crete. Annals of Applied Biology 102, 251–256. Martyn, R.D. and Hartz, T.K. (1986) Use of soil solarization to control Fusarium wilt of watermelon. Plant Disease 70, 762–766. Materrazzi, A., Triolo, E., Vannacci, G. and Scaramuzzi, G. (1987) The use of soil solar heating for controlling neck rot of greenhouse lettuce, Colture Protette 16, 51–54. Middleton, L.A. and Lawrence, N.J. (1995) The use of dazomet via the “planting through” technique in horticultural crops, Acta Horticulturae 382, 86–103. Oliveira, H. (1992) Evaluation of soil solarization for the control of Fusarium wilt of tomato, in E.C. Tjamos, G.C. Papavizas. and RJ. Cook (eds.). Biological Control of Plant Diseases. Progress and Challenges for the Future, NATO ASI Series A, Life Sciences, 230, Plenum Press, New York, pp. 69– 73. Phillips, A.J.L. (1990) The effects of soil solarization on sclerotial populations of Sclerotinia sclerotiorum. Plant Pathology 39, 38–43. Porter, I.J. and Merriman, P.R. (1985) Evaluation of soil solarization for control of root diseases of row crop in Victoria, Plant Pathology 34, 108–118. Ristaino, J.B., Perry, K.B. and Lumsden. R.D. (1991) Effect of solarization and Gliocladium virens on sclerotia of Sclerotium rolfsii, soil microbiota and incidence of southern blight of tomato, Phytopathology 81, 1117–1124. Ristaino, J.B. and Thomas, W. (1997) Agricultural MBr, and the ozone hole: Can we fill the gaps? Plant Disease 81, 964–977. Jordá, C., Alfaro, A., Aranda, M.A.. Moriones, E. and García-Arenal,

References

47.

48.

49.

50. 51.

52.

53.

54.

55. 56. 57.

58.

263

F. (1992) An epidemic of cucumber mosaic virus plus satellite RNA in tomatoes in Eastern Spain, Plant Disease 76, 363–366. Luis-Arteaga, M., Rodríguez-Cerezo, E., Fraile, A., Sáez, E. and García-Arenal, F. (1996) Different tomato bushy stum virus strains cause disease outbreaks on solanaceous crops in Spain, Phytopathology 86, 535–542. Mansour, A. and Al-Musa, A. (1992) Tomato yellow leaf curl virus: Host range and virus-vector relationships. Plant Pathology 41, 122– 125. Mehta, P., Wyman, J.A., Nakhla, M.K. and Maxwell, D.P. (1994). Transmission of tomato yellow leaf curl geminivirus by Bemisia tabaci (Homoptera: Aleyrodidae), J. of Economical Entomology 87,1291– 1297. Mink, G.I. (1993). Pollen- and seed-transmitted viruses and viroids, Annual Review of Phytopathology 31, 375–402. Murphy, F.A., Fauquet, C.M., Bishop, D.H.L., Ghabrial, S.A., Jarvis, A.W., Martelli, G. P., Mayo, M.A. and Summers, M.D. (eds.) (1995) Virus taxonomy: Classification and nomenclature of viruses, Archives of Virology Suppl. 10. Nolan, P.A. and Campbell, R.N. (1984) Squash mosaic virus detection in individual seeds and seed lots of cucurbits by enzyme-linked imnumosorbent assay. Plant Disease 68, 971–975. Scarlett, C.M., Fletcher, J.T., Roberts, P. and Lelliott, R.A. (1978) Tomato pith necrosis caused by Pseudomonas corrugata n. sp., Annals of Applied Biology 88,105–114. Schneid, R.W. and Grogan, R.G. (1977) Bacterial speck of tomato: Sources of inoculum and establishment of a resident population, Phytopathology 67, 388–394. Sherf, A.F. and McNab, A.A. (1986) Vegetable Diseases and their Control, John Wiley and Sons, New York. Sitterly, W.R. (1978). Powdery mildew of cucurbits, in D.M. Spencer (ed.), The Powdery Mildews, Academic Press, New York. Baath, E. (1991) Tolerance of copper by entomogenous fungi and the use of copper-amended media for isolation of entomogenous fungi from soil, Mycological Research 95(9), 1140–1142. Barrett, K.L., Grandy, N., Harrison, EG., Hassan, S.A. and Oomen, P. (eds.) (1994) SETAC Guidance Document on Regulatory Testing

264

59. 60.

61. 62.

63.

64.

65.

66.

67. 68.

69. 70.

Greenhouse Pest Management

Procedures for Pesticides with Non-Target Arthropods, ESCORT (European Standard Characteristics of Beneficials Regulatory Testing) Workshop, Wageningcn, The Netherlands, 28–30 March 1994, Society of Environmental Toxicology and Chemistry, Saffron Walden. Bartlett, B.R. (1964) Toxicity of some pesticides to eggs, larvae and adults of the green lacewing, Chrysopa carnea, J. of Economic Entomology 57, 366–369. Bathon, H. (1996) Impact of entomopathogenic nematodes on nontarget hosts, Biocontrol Science and Technology 6, 421–434. Biobest (1998) Side Effects of Pesticides on Bumblebees and Beneficials, Biobest Biological Systems Information Booklet, Biobest, Westerloo, Belgium. Blümel, S., Bakker, F. and Grove, A. (1993) Evaluation of different methods to assess the side effects of of pesticides on Phytoseiulus persimilis A.H., Experimental and Applied Acarology 17(3), 161–169. Blümel, S. and Stolz, M. (1993) Investigations on the effect of insect growth regulators and inhibitors on the predatory mite Phytoseiulus persimilis A.H. with particular emphasis on cyromazine, J. of Plant Diseases and Protection 100(2), 150–154. Cahill, M., Byrne, F.J., Denholm, I., Devonshire, A.L and Gorman, K.J. (1994) Insecticide resistance in Bemisia tabaci, in Extended Summaries SCI Pesticides Group Symposium Management of Bemisia tabaci, Pesticide Science 42, 135–142. Celli, S., Bortolotti, L., Nanni, C., Porrini, C. and Sbrenna, G. (1997) Effects of the IGR fenoxycarb on eggs and larvae of Chrysoperla cornea (Ncuroptera, Chrysopidae). Laboratory test, in P.T. Haskell and P.K. McEwen (eds.), New studies in Ecotoxicology, The Welsh Pest Management Forum, Cardiff, pp. 45–49. Cohen, Y., Reuveni, M. and Samoucha, Y. (1983) Competition between metalaxyl-resistant and -sensitive strains of Pseudoperonospora cubensis on cucumber plants, Phytopathology 73, 1516–1520. Croft, B.A. (1990) Arthropod Biological Control Agents and Pesticides, John Wiley & Sons, New York. Croft, B.A. and Strickler, K. (1983) Natural enemy resistance to pesticides: Documentation, characterization, theory and application,

References

71.

72.

73.

74.

75.

76.

77.

78.

79.

80.

81.

265

in G.P. Georghiou and T. Saito (eds.), Pest resistance to pesticides, Plenum Press, New York, pp. 669–702. Croft, B.A. and van de Baan, H.E. (1988) Ecological and genetic factors influencing evolution of pesticide resistance in tetranychid and phytoseiid mites, Experimental and Applied Acarology 4, 277–300. Elad, Y. and Shtienberg, D. (1995) Botrytis cinerea in greenhouse vegetables: Chemical, cultural, physiological and biological controls and their integration, Integrated Pest Management Reviews 1, 15–29. Elad, Y., Yunis, H. and Katan, T. (1992) Multiple fungicide resistance to benzimidazoles, dicarboximides and diethofencarb in field isolates of Botrytis cinerea in Israel, Plant Pathology 41, 41–46. Elzen, G.W. (1989) Sublethal effects of pesticides on beneficial parasitoids, in P. Jepson (ed.), Pesticides and non-target invertebrates, Incept, Wimborne Dorset, pp. 129–150. Fournier, D., Pralavorio, M., Berge, J.B. and Cuany, A. (1985) Pesticide resistance in Phytoseiidae, in W. Helle and M.W. Sabelis (eds.), World Crops Pests, Spider Mites, Their Biology, Natural Enemies and Control, Vol. 1B, Elsevier Publishers, Amsterdam, pp. 423–432 Fransen, J.J. and van Lenteren, J.C. (1993) Host selection and survival of the parasitoid Encarsia formosa on greenhouse whitefly Trialeurodes vaporariorum in the presence of hosts infected with the fungus Aschersonia aleyrodis, Entomologia Experimentalis et Applicata 69, 239–249. Georghiou, G.P. (1983) Management of resistance in arthropods, in G.P. Georghiou and T. Saito (eds.), Pest resistance to pesticides, Plenum Press, New York, pp. 769–792. Georghiou, G.P. and Mellon, R.B. (1983) Pesticide resistance in time and space, in G.P. Georghiou and T. Saito (eds.), Pest Resistance to Pesticides, Plenum Press, New York, pp. 1–47. Goodwin, S. and Wellham, T.M. (1992) Comparison of dimethoate and methidathion tolerance in four strains of Phytoseiulus persimilis (Athias-Henriot) (Acarina: Phytoseiidae) in Australia, Experimental and Applied Acarology 16 (3), 255–261. Gullino, M.L., Aloi, C. and Garibaldi, A. (1989) Influence of spray schedules on fungicide resistant populations of Botrytis cinerea Pers. on grapevine, Netherlands J. of Plant Pathology 95(Suppl.1), 87– 94. Hassall, K.A. (1982) The chemistry of pesticides, Verlag Chemie,

266

82.

83.

84.

85.

86.

87.

88.

89.

90. 91.

92.

Greenhouse Pest Management

Weinheim, Basel. Strider, D.L. (1969) Bacterial Canker of Tomato Caused by Corynebacterium michiganense: A Literature Review and Bibliography, Technical Bulletin No. 193, North Carolina Agricultural Experimental Station, Raleigh, NC. Okada. Y. (1986) Cucumber green mottle mosaic virus, in M.H.V. van Regenmortel and H. Fraenkel-Conrat (eds.), The Plant Viruses. Vol. II: The Rod-shaped Plant Viruses, Plenum Press, New York, pp. 267– 281 Zitter, T.A. and Simons, J.N. (1980) Management of viruses by alteration of vector efficiency and by cultural practices, Annual Review of Phytopathology 18, 289–310 Maas, J.L. (1984) Anthracnose fruit rots (black spot), in J.L. Maas (ed.), Compendium of Strawberry Diseases, APS Press, St Paul, Minn., pp. 57–60. Madden, L.V., Wilson, L.L., Yang, X. and Ellis, M.A. (1992) Splash dispersal of Colletotrichum acutatum and Phytophthora cactorum by short-duration simulated rains, Plant Pathology 41, 427–436. Malais, M. and Ravensberg, W.J. (1992) Knowing and Recognizing the Biology of Glasshouse Pests and their Natural Enemies, Koppert B.V. Publ., Berkel en Rodenrijs. McNicol, R.J. and Gooding, H.J. (1979) Assessment of strawberry clones and seedlings for resistance to Sphaerotheca macularis (Wall ex Frier), Horticultural Research 19, 35–41. Peng, G., Sutton, J.C. and Kevan, P.G. (1992) Effectiveness of honey bees for applying the biocontrol agent Gliocladium roseum to strawberry flowers to suppress Botrytis cinerea, Canadian J. of Plant Pathology 14, 117–129. Penes, O.S. (1962) Studies on strawberry mildew caused by Sphaerotheca macularis (Wallr. ex Frier) Jaczewski. II. Host-parasite relationships on foliage of strawberry varieties, Annals of Applied Biology 50, 225–233. Powelson, R.L. (1960) The initiation of strawberry fruit rot caused by Botrytis cinerea, Phytopathology 50, 491–494. Riudavets, J. (1995) Predators of Frankliniella occidentalis (Perg.) and Thrips tabaci Lind.: A review, Wageningen Agricultural University Papers 95-1, 43–87. Riudavets, J. and Castañé, C. (1994) Abundance and host plant preferences for oviposition of Onus spp. (Heteroptera: Anthocoridae)

References

93. 94.

95.

96. 97.

98.

99. 100.

101. 102. 103. 104. 105.

106.

267

along the Mediterranean coast of Spain, IOBC/WPRS Bulletin 17(5), 230– 236. Rose, D.H. (1924) Leather rot of strawberries, J. Agricultural Research 28, 357–375. Sannino, L., Balbiani, A., Lombardi, P. and Avigliano, M. (1996) Spodoptera littoralis: A harmful pest of the herbaceous crops, Informatore Agrario 53(18), 76–79. Scopes, N.E.A. (1985) Implications for biological control on intensively grown outdoor crops. Strawberries, in N.W. Hussey and N.E.A. Scopes (eds.), Biological Pest Control. The Glasshouse Experience, Blandford Press, Poole, pp. 190–191. Servadei, A., Zangheri, S. and Masutti, L. (1972) General and Applied Entomology, Cedam Publ., Padova. Smith, B.J. and Black, L.L. (1990) Morphological, cultural, and pathogenic variation among Colletotrichum species isolated from strawberry, Plant Disease 74, 69–76. Strand, L.L. (1994) Integrated Pest Management for Strawberries, University of California, Div. Agrjc. Nat. Res. Publ. 3351, Oakland, Cal. Sutton, J.C. (1994) Biological control of strawberry diseases, Advances in Strawberry Research 13, 1–12. Sutton, J.C. (1995) Evaluation of microorganisms for biocontrol: Botrytis cinerea on strawberry, a case study, in J.H. Andrews and I.C. Tommerup (eds.), Sustainability in Plant Pathology, Advances in Plant Pathology, Vol. 11, Academic Press, London, pp. 173–190. Sutton, J.C. and Peng, J. (1993) Biocontrol of Botrytis cinerea in strawberry leaves, Phytopathology 83, 615– 621. Tommasini, M.G. and Nicoli, G. (1996) Evaluation of Onus spp. as biological control agents of thrips pests. Further experiments on the existence of diapause in Onus laevigatus, IOBC/WPRS Bulletin 19(1), 183– 186. Tremblay, E. (1986) Applied Entomology, Vol. 2/2, Liguori Ed., Napoli. Tropea Garzia, G. (1997) Recent advances in the integrated control of noctuids harmful to protected crops, Notitiario sulla Protezione delle Piante (nuova serie) 7, 273–283. Vacante, V. and Nucifora, A. (1987) Possibilities and perspectives of

268

107.

108. 109. 110.

111.

112.

113.

114.

115. 116.

Greenhouse Pest Management

the biological and integrated control of the two spotted spider mite in the Mediterranean greenhouse crops, IOBC/WPRS Bulletin 10(2), 170–173. van den Meiracker, R.A.F. (1994) Induction and termination of diapause in Onus predatory bugs, Entomologia Experimentalis et Applicata 73, 127–137. Wilhelm, S. and Paulus, A.O. (1980) How soil fumigation benefits the California strawberry industry, Plant Disease 64, 264–270. Wright, W.R., Beraha, L. and Smith, M.A. (1966) Leather rot on California strawberries, Plant Disease Reporter 50, 283–287. Yang, X., Madden. L.V., Reichard, D.L., Wilson, L.L. and Ellis, M.A. (1992) Splash dispersal of Colletotrichum aculalum and Phytophthora cactonun from strawberry fruit by single drop impactations, Phytopathology 82, 332–340. Ellouze, W., Mishra, V .(2018). Emerging Virus and Viroid Disease Risks on Greenhouse Crops. Alberta Agriculture and Forestry, Greenhouse Section, Crop Diversification Centre SouthBrooks, Alberta. Johansen N.S., Vanninen I., Pinto D.M., Nissinen A.I. and Shipp L. (2011) In the light of new greenhouse technologies: 2. Direct effects of artificial lighting on arthropods and integrated pest management in greenhouse crops. Ann Appl Biol 159, 1–27 . Panwara, N.L.,.Kaushika, S.C and Kothari, S. ( 2011) Solar greenhouse an option for renewable and sustainable farming. Renewable and Sustainable Energy Reviews 15, 3934-3945. Kudapaa , H.A, Ramalingam, A. A. B , Nayakot, S. et al. (2013) Functional genomics to study stress responses in crop legumes: progress and prospects. Functional Plant Biology, 40, 1221–1233. Singh S., B. ,Singh, A.P (2015). Nematodes: A Threat to Sustainability of Agriculture. Procedia Environmental Sciences 29, 215-216. Nyongesa, M W., Coosemans, J . , Kimenju, J W. (2007) Evaluation of Verticillium chlamydosporium and Arthrobotrys oligospora for biological control of Meloidogyne incognita in celery and tomato. J. Trop. Microbiol. Biotechnol. 3 .51-58

INDEX A Aphid infestations 19 Appropriate transfer 251 Appropriate transformation 109 Atmospheric temperature 6 Attract insect pests 115

B Bacterial diseases 90 Biological control 66, 69, 96, 99, 225 Biological control agents 201, 205 Biological control comprises 144 Biological control program 145, 148, 149, 155 Biological vector 39, 40 Biological vectors 38 Broad activity modes 137 Broad-spectrum fumigants 88

C Calculate resistance 191 Calibration process 106 Carbon dioxide blanket termed 6 Chemical fungicides 206

Chrysanthemum 66, 67, 77, 215, 218, 219, 221 Climate stabilizing equipment 171 Colonizing root system 67 Combating virus transmission 40 Combined toxicity 140 Combine various management practices 55 Common disease 73 Compatible resistant 189 Conceptual framework 95 Contaminated food 201 Controlled environment 2, 3, 6, 7 Critical segment 251 Crop performance 87, 88 Cropping system 117, 118, 119 Cross protection 55 Cucumber crops 253 Cucumber Mosaic virus 41 Cultivation procedures 109 Cultural practices 58, 60, 62 Cyclamen and Chrysanthemum 60

D Damage relationships 94, 95, 96, 97, 98

270

Greenhouse Pest Management

Defense mechanisms 185, 186, 192 Designated greenhouse temperature 163 Development period 28 Diamondback 22 Disease development 91 Disease management 163 Dispersal mechanisms 38, 55 Distinctive measurements 108 Diverse approach 107

E Eggplant 64, 67, 71, 73, 76 Environmental conditions 2, 4 Environmental parameters 95, 97, 98 Epidemiological implications 88 Exhibit horizontal dispersion 192 Exhibit unilateral 58 Exploring host-plant resistance 184

F Favorable weather patterns 163 Favor enhanced female reproduction 122 Field estimation 110 Final population 84 Foraging behavior 145, 147, 155, 159 Fruit exhibit mottling 53 Fungal sporulation 165, 179

G General symptoms 215 Geographic location 4 Glass greenhouses 9 Global problem 133 Greenhouse construction 11

Greenhouse environment 145 Greenhouse operation 163, 164 Greenhouse producers 135, 139, 141 Greenhouse production systems 114 Greenhouses 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 Greenhouse structures 39, 53 Greenhouse until the parasitoids 253 Growing medium 126, 131 Growth medium 122, 124

H Handling insect problems 163 Heating system 166 Highlighted significant diseases 79 High-pressure sodium lamps (HPSLs) 119 High volume (HV) 205 Homologous genetic organization 53 Host-parasite system 191 Host-plant resistance 184, 187, 188, 189, 191, 196 Human influence 93 Humidity and temperature 92 Hydroponic cropping 253 Hypersensitive response 186

I Infection cycle 90, 92, 93 Infection exhibit symptoms 60 Inorganic media 85 Insect migration 123 Install greenhouse industries 201 Integrated pest management 82, 250 Integrated pest programs 83

Index

L Laboratory environment 146 Leafhoppers 25, 26 Leafhoppers possess piercing 26 Light-emitting diodes 119

M Machinability 11 Magnitude 90, 92, 93, 94, 95, 99 Management practice 114 Management strategies 4, 5, 84, 114, 119, 136 Marketability 23 Maximizing productivity 163 Mediterranean 250, 251, 252, 253, 257, 258 Mediterranean basin 168 Melon plants systemically 52 Microbial degradation 88 Microclimatic 92, 93 Mild strain reversion 55 Minimal infestations 213 Moderate temperatures 67, 77 Monitor adults 222 Monitored regularly 154 Monitoring of resistance 112 Morphological features 84

N National Oceanic and Atmospheric Administration 6 Natural enemies 144, 145, 146, 147, 148, 149, 150, 153, 155, 156, 157, 158, 159, 160 Nematode distribution 83 Nematode populations 83, 85, 86, 88 Neuromuscular activity 88 Normal procedures 111

271

Nutrient deficiencies 92

O Optimal temperature 75, 78 Organic matter 222 Organic product gathering 257 Organism grows 184 Orotected agriculture 2

P Parasitic nematodes 82 Particular pest-plant interaction 94 Passive scouting comprises 115 Peculiar property 19 Pesticide application 114, 117, 118 Pesticide suppression 127 Photosynthesis 119 Physical control and sanitation strategies 114 Physiological selectivity 201 Plant fluids 18, 19, 26, 30, 35 Plant-parasitic nematode 85 Plant populations 190 Plant quality 6 Plastic greenhouses 65 Polycarbonate rigid panels 8 Population biology 90, 98 Population densities 84, 85, 86 Population dynamics 102, 107, 114, 117 Potassium fertilizers 191 Potential issue pertaining 141 Preventive maintenance programs 171 Primary symptom 74 Process of sanitation 122, 123 Propagating materials 72 Proportion of carbon dioxide 6

272

Greenhouse Pest Management

Public except transgenic cultivars 194

Q Quality control (QC) 145

R Regression analysis 94, 95, 98 Regulatory process 144 Relative humidity 4, 92 Render management harder 163 Repeated pesticide applications 132, 133 Resistance mechanisms 187 Responsible for induction 53 Root-knot nematode 83, 86 Rotation technique 85

S Scouting techniques comprise 116 Segregation of populations 187 Semi-field conditions 202 Separate propagation facilities 165 Sequential sampling plans 108 Soil amendments 86, 88 Soil borne pathogens 198 Soil fumigation 199 Soil temperatures 88 Spatial distribution 102, 110, 111 Species identification 228 Species of microorganism 202 Spray application 128 Spray treatments 206

Squash Mosaic Virus 50, 51 Strawberries 257 Structural complexity 162, 164 Supplemental food source 146 Supplemental residual activity 128 Supply natural enemies 149 Suppressive substrates 66 Susceptible life stages 131, 135 Susceptible species 53

T Theoretical distribution 111 Toxicology 199 Transmission inside 123 Transmitting fungal diseases 223

U Uniform light intensity 8

V Various mechanisms 134 Vector/viral transmission relations 40 Viral Infection 38 Visual class system 104 Visual estimation 109

W Water condensation 77 Water substance 252

Y Yield relationship 94, 96, 97