Erysiphe deutziae (Bunkina) U. Braun & S. Takam. is powdery mildew fungus that is currently spreading in Europe. The anamorph of this species has been found in France, Germany, Poland and Switzerland on Deutzia sp. (cult.), Deutzia × magnifica (Lemoine) Rehder and Deutzia scabra Thunb. The morphology, taxonomy and worldwide distribution of Erysiphe deutziae are described, illustrated and discussed.