Integrating cultural control methods for tomato late blight (Phytophthora infestans) in Uganda

Cultural control measures against tomato late blight (Phytophthora infestans) were evaluated in six field experiments over 3 years in Uganda. Each experiment included sanitation (removal of diseased plant tissues), fungicide (mancozeb) application, and an untreated control, as standard treatments. Late blight incidence and severity were greatly reduced by sanitation, without reducing the number of healthy leaves; however, tomato growth and production were adversely affected. Fungicide treated plants retained the highest numbers of flowers and attached fruits and gave the highest yields. Three cultural practices were evaluated in repeated experiments for their effectiveness in alleviating the adverse effects of sanitation. Tomatoes grown within plastic shelters early in the production cycle were taller, and had more healthy leaves than those grown late. The numbers of diseased leaves and disease severity were equally low in sanitation alone and plastic shelter/with sanitation treatments. Flower and fruit production were significantly higher when tomatoes were grown under early shelters with sanitation than with sanitation alone. Planting density was increased without significant effects on late blight and tomato growth and production. Intercropping tomato with soybean (Glycine max) or sesame (Sesamum indicum), with sanitation, limited late blight development, but taller intercrops suppressed tomato growth and production. Integrated treatments (combining plastic shelters, a sesame intercrop and high tomato planting density) were evaluated, with and without sanitation, against the fungicide mancozeb. The mean numbers of healthy leaves in the integrated treatments were not significantly less than with fungicide treatment. Late blight incidence and severity were higher in the integrated plots without than with sanitation. The numbers of flowers and attached fruits were not significantly less in integrated treatments than in fungicide treated plots, but tomato yield was highest with fungicide treatment.