Towards the development of integrated cultural control of tomato late blight (Phytophthora infestans) in Uganda

Tomato ( Lycopersicon esculentum ) is a major vegetable crop in Uganda. Moneymaker, Marglobe, Heinz and Roma are the major commercial varieties grown in the country, the first two being the most popular. Late blight ( Phytophthora infestans ) is the most important disease of Ugandan tomatoes. Tomato cultivation in Uganda is mostly done continuously throughout the year which perpetuates P. infestans survival and sources of inoculum. Late blight in Uganda is predominately controlled by fungicides and the most commonly used fungicide is Dithane M-45 (mancozeb). However, there are virtually no data available on the effectiveness of control of the disease on tomatoes in the country.This research was aimed at developing integrated disease management practices, which avoid where possible the use of fungicides, for late blight disease in Uganda. In the Ugandan situation, this effectively means a range of cultural control practices. New isolation techniques which make use of healthy, and diseased tomato fruits to isolate the pathogen from tomatoes were developed and used in the research. Ugandan isolates of P. infestans were found to be of A1 mating type but this was on the basis of a very limited number of samples. The study indicated that sanitation can reduce late blight disease incidence and severity but causes adverse effects on the crop in terms of height, flower formation, fruit numbers and yield.The use of polythene shelters, intercropping, or high tomato planting densities each combined with sanitation helped to alleviate the adverse effect of sanitation and reduced the disease levels even further. The fungicide (Dithane M-45) was only partially effective in controlling late blight by delaying epidemics for about 2 weeks. Nevertheless the fungicide consistently gave higher numbers of fruits and yield than any of the cultural practices, with or without sanitation. If cultural practices are to substitute for fungicides within an integrated disease management system, then further development work is required