Erysiphe cruciferarum is a plant pathogen of the family Erysiphaceae, which causes the main powdery mildew of crucifers, including on "Brassica" crops, such as cauliflower, cabbage, broccoli, and Brussels sprouts. "E. cruciferarum" is distributed worldwide, and is of particular concentration in continental Europe and the Indian subcontinent. "E. cruciferarum" is an ascomycete fungus that has both sexual and asexual stages. It is also an obligate parasite that appears to have host specificity; for example, isolates from turnip will not infect Brussels sprout, and vice versa. While being a part of the family Erysiphaceae, it belongs to those members in which the conidia are formed singly and whose haustoria are multilobed.