DECISION-MAKING IN THE CONTROL OF VEGETABLE PESTS IN THE THAMES VALLEY BY MD. OUSOH BIN MAMAT Dip. Agric. (Malaysia), B.Sc. (L.S.U), M.Sc. (P.S.U) Thesis submitted for the degree of Doctor of Philosophy of the University of London and for the Diploma of Imperial College Department of Pure and Applied Biology, Imperial College, Silwood Park, Ascot, Berkshire OCTOBER 1984- -ii - ABSTRACT This thesis investigates the problem of pest manage­ ment on vegetable crops in the Thames Valley area. Various philosophical approaches to problem solving research are discussed, revealing the underlying principles of each approach. A decision-analysis approach is employed in this investigation, starting with a descriptive analysis of the vegetable pest management problem, using information gathered from the literature, personal discussion , farm record exam­ ination, and intensive studies on a few selected farms. To obtain further information on current pest management problems in the Thames Valley, an interview survey of 20 vegetable growers in the area was conducted. One outcome of this survey was to reveal the importance of aphid pests in the area, especially on autumn cabbages. To investigate this problem in more detail, an intensive study was con­ ducted in growers' fields to examine the factors thought to be responsible for the aphid problem in the area. This included monitoring aphids, their parasites and predators; assessing the percentage kill of aphids; assessing spray droplet coverage on plants; and calibrating growers' sprayers. Finally, the findings of these investigations are used to suggest recommendations for future aphid control in autumn cabbages and further complementory research to this thesis. i ii TABLE OF CONTENTS Page ABSTRACT ..................................................... ii PREFACE ..................................................... ix SECTION Is DECISION-ANALYSIS APPROACH TO VEGETABLE PEST MANAGEMENT PROBLEMS ............... 1 CHAPTER Is AN INTERPRETIVE REVIEW OF VARIOUS APPROACHES TO AGRICULTURAL RESEARCH ... 2 1.1. Introduction .................................. 2 1.2. The IRRI On-Farm Cropping System Approach 6 1.3. The CIMMYT On-Farm Farming System Research Approach 9 1.4. The Decision-Analysis Approach to Pest Management Research 14 1.5. Conclusion .................................. 19 CHAPTER 2: VEGETABLE PRODUCTION IN UNITED KINGDOM AND THAMES VALLEY ..................... 21 2.1. Introduction .................................. 21 2.2. Vegetable Production in the United Kingdom 22 2.3. Changes in the United Kingdom Vegetable Sector ........................................ 22 2.4. Vegetable Production in the Thames Valley Area ......................... ......... 27 CHAPTER 3: DESCRIPTIVE ANALYSIS OF THE VEGETABLE PEST SYSTEM ............................ 30 3.1. Introduction .................................. 30 3.2. The Structure of the System ............... 30 3.2.1. The components of the system ......... 30 3.2.2. Cropping schedule/cropping system ... 33 iv 3.3. The Dynamics of the Vegetable Pest System 35 3.3.1. Time profile for some of the major pest components .................................. 35 3.3.2. The effects of pests on vegetables ... 38 3.3.3. The effects of parasites and predators on vegetable pests ......................... 40 3.3.4. The effects of pesticides on components of the vegetable pests .................... 40 3.4. Management and the Vegetable Pests System 43 3.4.1. The objectives and constraints of a vegetable grower ............... ... ... 44 3.4.2. Grower’s perceptions of vegetable pests 45 3.4.3. Control measures for vegetable pests ... 46 3.5. Conclusion ... ............................ 47 SECTION II: INTERVIEW SURVEY OF THAMES VALLEY GROWERS .............................. 50 CHAPTER 4: INTERVIEW SURVEY OF THAMES VALLEY GROWERS: BACKGROUND INFORMATION ... 51 4.1. Introduction .................................. 51 4.2. Aims and Operation of the Survey ......... 51 4.3. Results and Discussion of the Survey ... 55 4.3.1. The vegetable Farm Agroecosystem ... ... 55 4.3.1.1. Farm size .................................. 55 4.3.1.2. Experience in vegetable growing .......... 57 4.3.1.3. The predominant soil types on vegetable farms ... ... 58 4.3.1.4. Types of vegetable grown ... ... ... 5 9 4.3.1.5. Methods of planting vegetables .......... 66 4.3.1.6. Crop irrigation practices ............... 70 V 4.3.1.7. Crop rotation practices ................ 71 4. 3.1.8. Marketing outlets ... ... ... ... 73 4.3.2. Conclusion .................................. 73 CHAPTER 5: INTERVIEW SURVEY OF THAMES VALLEY GROWERS: PESTS AND PEST CONTROL ..................... 76 3.1. Introduction ................................ 76 5.2. Major Pest Problems of Vegetables in Thames Valley 76 5.3. The Reasons Why Pests Become a Problem ... 80 5.4. Crop Protection Practices Currently Adopted by Growers ... ... ................ ... ... 82 5.4.1. Clubroot of brassicas ..................... 82 5.4.2. Fungal diseases of leeks and onions ... 85 5.4.3. Cabbage aphids 85 5.4.4. Cabbage rootfly ............................ 90 5.4.5. Caterpillars .................................. 90 5.4.6. Groundsel and couch grass ............... 93 5.5. The Cost of Current Pest Control Programmes 93 5.6. Growers Crop Inspection Practices ......... 94 5.7. Problem Faced by Growers in Carrying out their Crop Protection Programmes ......... 95 5.8. Grower's Opinions on their Present Crop Protection Programmes Could be Improved ... 98 5.9. Sources of Advice and Information Used by Growers ......... 98 5.10. The Problems of Cabbage Aphids ......... 102 SECTION III: INVESTIGATION OF FACTORS DETERMINING THE PROBLEM OF CABBAGE APHIDS ON COMMERCIAL FARMS IN THAMES VALLEY ... 104 CHAPTER 6: POPULATION STUDIES OF THE CABBAGE APHIDS, THEIR PARASITES AND PREDATORS IN COMMERCIAL CABBAGE FIELDS ......... 105 6.1. Introduction .................................. 105 6.2. Biology of the Aphids .................... 106 6.2.1. The cabbage aphid ............................ 107 6.2.2. The peach-potato aphid ... ... ... ... 112 6.2.3. The potato aphid ........................... 113 6.3. Population Studies of the Cabbage Aphids, their Parasites and Predators in Commercial Cabbage Fields .................................. 114 6.3.1. Material and methods ..................... 115 6.3.2. Results and discussions ..................... 117 6.3.2.1. General trends in the development of live aphid and mummy population in a cabbage field without chemical control 117 6.3.2.2. Trends in the number of live aphids and mummies in commercial cabbage fields with chemical control ..................... 121 6.3.2.3. Changes in the percentage composition of alatae, apterae and nymphs in relation to crop stages and chemical control activities .................................. 128 6.3.2.4. Field counts of JD. rapae and their rate of parasitism ............................ 130 6.3.2.5. Field populations of predators ....... 136 6.3.2.6. The aerial population of alatae and the adult parasites and predators of aphid in cabbage fields 140 Vll 6.3.2.7. Changes in the percentage of the cabbage plants infested with aphids in relation to crop stages and chemical control ... 146 6.4-. C o n c l u s i o n ........................................ 150 CHAPTER 7: INVESTIGATION INTO GROWERS' CONTROL STRATEGIES ............................ 153 7.1. Introduction ... ............................ 153 7.2. Assessment of Field Percentage Kill of Aphids, Parasites and Predators Achieved by Commercial Vegetable Growers .............. 153 7.2.1. Method of study ... ... ... ... ... 154 7.2.2. Results and discussion ..................... 155 7.2.3. Conclusion .................................. 158 7.3. Aphid Distribution Within a Cabbage Plant at Various Stages of the Crops ............... 158 7.4. Assessment of Spray Coverage on Cabbage Plants in Commercial Vegetable Farms ... 161 7.4.1. Materials and methods ..................... 162 7.4.2. Results and discussion ..................... 165 7.4.3. Conclusion .................................. 167 7.3. Calibration of Conventional Tractor Mounted Medium Volume Sprayers Used by Commercial Vegetable Growers ............................ 168 7.3.1. Calibration method ... ... ... ... ... 170 7.5.2. Results, discussion and conclusion ... 171 7.5.2.1. Types and age of nozzle ... ... ... 171 7.5.2.2. Number of nozzles per boom and swath ... 173 7.5.2.3. Height of nozzles ............... ... 173 7.5.2.4. Actual volume sprayed and the percentage error made .................... ......... 174 v iii 7.6. Conclusion 175 SECTION IV: CONCLUSION .................................. 180 CHAPTER 8: RECOMMENDATION FOR FUTUREAPHID CONTROL 181 8.1. Introduction ... ............................ 181 8.2. The Timing of Chemical Application forAphid Control .................... ............ • 182 8.3. The Coverage of Spray Droplets on Cabbage Foliage ........................................ 190 8.4. The Methods of Chemical Application (Granules versus Spray) ..................... 192 8.5. The Choice of Chemicals ..................... 194 CHAPTER 9: RECOMMENDATION FOR FURTHER RESEARCH ... 198 9.1. Introduction .................................. 198 9.2. Recommendation on Further Complementary Research ........................................ 199 9.3. Appraisal of the A p p r o a c h ..................... 199 ACKNOWLEDGEMENTS ........................................ 202 REFERENCES 204 APPENDIX 1 218 ix PREFACE There are many Integrated Pest Management (IPM) projects that