Are millipedes a pest in low-input crop production in north-eastern Uganda? Farmers’ perception and experimentation Promotor: Prof. dr. ir. P.C. Struik Hoogleraar in de Gewasfysiologie Promotiecommissie: Prof. dr. K.E. Giller (Wageningen Universiteit) Prof. dr. P. Richards (Wageningen Universiteit) Prof. dr. ir. A. van Huis (Wageningen Universiteit) Prof. dr. ir. O. van Kooten (Wageningen Universiteit) Dit onderzoek is uitgevoerd binnen de C.T. de Wit onderzoekschool: Production Ecology and Resource Conservation. Are millipedes a pest in low-input crop production in north-eastern Uganda? Farmers’ perception and experimentation Ernst Ebregt Proefschrift ter verkrijging van de graad van doctor op gezag van de rector magnificus van Wageningen Universiteit, prof. dr. M.J. Kropff, in het openbaar te verdedigen op dinsdag 16 oktober 2007 des morgens te 11 uur in de Aula Ernst Ebregt (2007) Are millipedes a pest in low-input crop production in north-eastern Uganda? Farmers’ perception and experimentation. Ebregt, E. –[S.l.:s.n.]. Ill. PhD thesis Wageningen University. – With ref. – With summaries in English and Dutch. ISBN: 978-90-8504-733-9 Aan mijn vader Abstract Ebregt, E., 2007. Are millipedes a pest in low-input crop production in north-eastern Uganda? Farmers’ perception and experimentation. PhD thesis, Wageningen University, The Netherlands. With summaries in English and Dutch, 168 pp. Between 2000 and 2003, various studies were conducted to assess the impact of millipedes as pests in the production of sweet potato and other major crops in north-eastern Uganda. The overall objective of the research was to generate basic knowledge about pest status, biology, ecology, and behaviour of millipedes. A strategy was recommended for integrated production and pest management in sweet potato and other major crops, serving the needs of resource- poor farmers in low-input agricultural systems in north-eastern Uganda and eastern Africa. These studies included: (i) Field survey on farmers’ knowledge on sweet potato production and perception of millipede infestation; (ii) Field assessment of pests in sweet potato and other major crops conducted in the planting seasons of 2000 – 2002; (iii) Feeding activity of the East African millipede Omopyge sudanica Kraus, based on no-choice laboratory experiments, and (iv) Comparison of the indigenous cultural practices of piecemeal harvesting and storage roots ‘in-ground on plants’ with one-time harvesting after crop senescence in trials conducted in the planting seasons of 2002 – 2003. There was inadequate information about millipedes in general and possible control strategies in East Africa. Therefore a literature study was also done to gain more knowledge about this animal. From the 148 sweet potato (Ipomoea batatas (L.) Lam.) growers interviewed information was generated on sweet potato production and its constraints. Farmers considered sweet potato weevils (Cylas spp.) the most important pests, followed by rats (Spalax spp.) and millipedes. The impact of millipedes was also serious in other major food and cash crops, such as cassava (Manihot esculenta Crantz), groundnut (Arachis hypogaea L.) and maize (Zea mays L.). Separation of plots over time and space is often not practised. Millipede incidences depended on the frequency of millipede hosts in the crop rotation. Groundnut planted after sweet potato showed high levels of millipede attack. Millipede incidence was often associated with the incidence of sweet potato weevils. Measures to control sweet potato pests, like sanitation, were hardly implemented. Chemical insecticides were not used at all. Field experiments showed that millipedes of the species O. sudanica caused damage on planting material of sweet potato and on germinating and podding groundnut early in the first rainy season (March/April). Damage in maize occurred in both rainy seasons. Storage roots of sweet potato were hardly affected by millipedes when harvested 5 months after planting. However, when storage roots were stored ‘in-ground on plants’ during the prolonged dry season sweet potato weevils facilitated millipede damage. No-choice feeding activity laboratory experiments showed that O. sudanica efficiently utilized the grain crop diets groundnut and maize for its growth. The species also consumed storage roots of sweet potato. The research revealed how difficult it is to obtain reliable, quantitative data on the feeding habits of millipedes. Piecemeal harvesting used to be done up to final harvest. It is revealed that this practice was only useful during a limited period of time. When piecemeal harvesting continued up to 5 months or more, it could coincide with the onset of the dry season, i.e. when sweet potato weevils invade the above-ground sweet potato plant parts. When the population of weevils is too high piecemeal harvesting can no longer be used as a control measure. From the results in this thesis some important issues have arisen which can be implemented in a pest control programme of the sweet potato crop. The research activities presented in this thesis have led to recommendations for improving integrated sweet potato production and pest management aimed at the needs of the resource-poor farmers in low-input agricultural systems of East Africa. Keywords: Crop rotation, farmers’ knowledge of millipedes, host crops, integrated crop production and pest management, Ipomoea batatas, millipedes, no-choice feeding activity of millipedes, Omopyge sudanica, piecemeal harvesting, sweet potato, sweet potato weevils. Preface The research described in this thesis was carried out in north-eastern Uganda between 2000 and 2003. Without the support of the farmers, the research assistants in the field, and staff of the Arapai Agricultural College, it would not have been possible having conducted this work. A great many people, in Uganda and elsewhere, encouraged me to fulfil my endeavours. It is impossible to thank them all, but I would like to thank those who played a key role. Without Dr. Benson Odongo from the Namulonge Agricultural and Animal Research Institute (NAARI) I would probably never had the chance to begin this undertaking. He guided me in setting up the research proposal and he was the person who discussed with me the experiments to be conducted and their loopholes. Thanks for all the hospitality I received from you and your wife during my stays at your residence. Above all, I am deeply in debt with Prof. Paul C. Struik of the Crop and Weed Ecology Group, who supported, encouraged and supervised me from the very beginning. The door of your office was always open, encouraging me to enter without anxiety. You always took your time. After leaving your office I always had the exited feeling to be able to continue in my efforts to get the articles ready to be published. Your swiftness in going through drafts, even during your journeys to a far away destination, often surprised me, but is so much appreciated. I was very lucky having you as my supervisor. Dr. David Rees, the project coordinator of the Department of International Development (DFID), is thanked for financing a part of the interviews and for supporting and guiding part of the work. The support and help of Dr. C.A.W. Jeekel are never forgotten. He identified some millipede species, which affected the sweet potato, groundnut and maize. I enjoyed the ‘lectures’ and he triggered my interest to have a closer look at the anatomy of the millipede. He explained the complexity of distinguishing female from male millipedes, the tiny differences between species and the difficulty of identifying the larvae. The gained knowledge was very useful to give body to my articles and made it possible to pass it on to some of my research assistants, who never attended school. Dr. Jeekel also taught me a few important home truths. I got the message. I am grateful for that. I would like to thank Ms Gon van Laar for editing the thesis, the layout and putting the chapters in the same format. I realize you were very busy with your own work, but still you were prepared to help me, as desperate I was in the final stadium of this thesis. Your work is highly appreciated. Please, continue to assist other students, as you play a crucial, and above all, an emotional role in the final steps of many years plodding and ‘sweet and tears’. Personally, I felt an enormous release when you said: “That ‘s it. Ready”. I am so grateful to you! I would also like to thank my colleagues at Arapai Agricultural College. In the first place all my gratefulness goes to Aisu Jonathan Oumo. He was my main assistant and friend during the work. Especially for being my guide during the so many trips to the farmers and the translation work in the field. I also like to thank Francis Onyilo for assisting me during the interviews with farmers in Lira District. Despite the hardships, we had a wonderful time out there and I learned a lot about the Teso and the Lango. Dr. Morris Oĉweda is acknowledged for reviewing earlier versions of a number of scripts and being the ‘logistic officer’ for organizing the college truck. I also like to thank Morris for the friendship, which even continues to last, in spite of the great distance between us. And from here, I like to tell you, that this friendship is very special for my family. One day we will meet again. I also like to thank Mr. M.M. Okiror, Mrs. Christine Okello, Mr. John Ochana, Mr. Aedeke and Mr. Odiman. Special thanks go to Mr. Ocam Sylvester, who managed the weather station at Arapai and in collecting rainfall data. I cannot forget our old friend David Okulimo. Early in the morning you were already in the field and you were the first who made note of some funny ‘worms’ eating your sweet potato vines in the vine nursery.