Prevalence of apple scab and powdery mildew infecting apples in Uganda and effectiveness of available fungicides for their management

Apple scab caused by Venturia inaequalis (Cooke) wint, and apple powdery mildew, caused by Podosphaera leucotricha (Ell. and Ev.), are the most important diseases of apples in Uganda. Control of apple scab and powdery mildew require the application of fungicides in absence of resistant apple cultivars. This study was conducted to identify effective control fungicides and to document the status of these diseases in south western Uganda. The survey results of 2012 indicated that scab incidence was highest in districts of Kanungu (71.90%), followed by Kisoro (48.14%), Kabale (41.03%), Buhweju (29.23%), Mbarara (28.75%) and Rukungiri (17.80%). The severity of apple scab measured as percentage leaf area affected ranged from 20.12 to 76.19%. Powdery mildew incidence ranged from 30.00 to 70.00% with severity score ranging from 14.63 to 76.19%. Fungicides containing  propineb (70% a.i), metalazyl (4% a.i) + macozeb (64% a.i), and bupirimate (25% a.i) were found to be effective at controlling apple scab with potential to reduce the disease severity by 61.11, 61.11 and 58.33%, respectively, while fungicides containing bupirimate (25% a.i), tebuconazole (43% a.i)  and propineb (58% a.i) + cymoxanil (4.8% a.i) were more effective in the control of powdery mildew with potential to reduce the infection by 55.95, 39.12 and 20.84%, respectively.   Key words: Apple scab, powdery mildew and fungicides.