Prevalence, incidence and severity of apple powdery mildew infecting apple trees in the Fes-Meknes Region, Morocco

Apple powdery mildew, Podosphaera leucotricha (Ell. And Ev.), highly infects apple trees in the Fes-Meknes region in Morocco. Disease survey was carried out during a fruit set stage of apples in late spring 2018. Three most popular cultivars in the region were assessed to investigate the incidence and severity of the disease. It was obvious that the cultivars were highly susceptible to powdery mildew (grand mean of leaf mildew: Starking Delicious, 17.1%; Golden Delicious, 13.5%; and Gala, 11.1%). The correlation between powdery mildew incidence and its severity was highly positive (r =0.90). We recorded the highest disease incidence in Tigrigra (21.5%) and the least in Sidi El Makhfi (4.10%). In view of ensuring good plant protection practices, we recommend that apple farmers carry out disease scouting and consider the action threshold before applying fungicide sprays. Keywords: Disease survey, Apple powdery mildew, Fes-Meknes region