Integrating of host resistance, cultural methods and fungidal application for the management of late blight of potatoes in Uganda

Late blight caused by Phytophthora infestans (Mont.) de Bary is the most damaging disease of potato in the highlands of Uganda. The objective of this study was to identify plausible disease management options for development of an integrated disease management (IDM) Package for late blight in Uganda. Two experiments were conducted. The first experiment evaluated the effect of potato variety, planting date and fungicide application on the late blight severity. Results indicated that planting early with respect to planting before or at beginning of the rains, produced the highest yields because the plants emerged and matured before late blight had built up to levels that could cause severe epidemics. However, when the late blight epidemic developed, it progressed faster on the mature potatoes such that within only a few days all the unsprayed plots were severely infected. Late planted potatoes had low disease as well as low yields because the weather conditions were not suitable for proper growth resulting in poor tuberisation and bulking. Of the 3 varieties tested, Kabale was found to be the most susceptible to late blight, although, it yielded better than either Victoria or Rutuku which had lower disease levels. Sprayed potatoes generally yielded better than the unsprayed ones. The second experiment evaluated the efficacies of two fungicides, Dithane M-45 and Ridomil, their combination, and spraying intervals for controlling late blight. Treatments that included Ridomil had the best disease control resulting in high yields. During the heavy rains, Dithane M-45 was not effective against late blight. The economic analysis revealed that application of Ridomil once (first) and Dithane M-45 subsequently was very effective and a good economic incentive because it was less cost and earned the highest marginal benefits when used at 14 and 21 days spraying intervals. An interval of 14 days, during the very wet seasons was effective in controlling late blight and resulted in economic yields.