Occurrence of powdery mildew of citrus in Japan

In April 1998, powdery mildew was found on two species of citrus (tankan mandarin and mandarin orange) in Kagoshima prefecture, Japan. White, powdery mycelial colonies appeared on leaves and young shoots. Young leaves specially were damaged severely, infected leaves eventually fell. Conidia were ovoid to cylindric, 25.0-41.6×12.5-18.7(-27.1)μm in size, borne singly on conidiophores erected on aerial mycelium. Appressoria on germ tubes were lobed. Cleistothecia were not observed. On the basis of the morphological characters of the conidial state, the fungus was proposed as an Oidium sp. of the Erysiphe polygoni type.