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.

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.

[5] 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.

Erysiphe cruciferarum exhibits typical powdery mildew characteristics, appearing as small radiating, diffuse colonies of superficial white mycelium on the surface of the leaf; usually both sides of the leaf show white, powdery fungal growth.

[8] Severe, advanced infections produce a dense white powdery covering of leaves, stems, and seed crop pods.

On cauliflower and cabbage, heavily diseased plants show chlorosis, early defoliation, and necrosis of the tips of young leaves.

Adding vegetative wind barriers can impede the spores' travel into the cultivated field and possibly lower the chance of infection.

[12] Erysiphe cruciferarum is also being studied for its ability to be used as a biological control to curtail garlic mustards whose growth is widely unchecked across the country.

Eventually, leaves infected with powdery mildew may turn yellow in color and proceed to die or fall off.

Certain biological fungicides, such as Serenade or sulfur products, can be used on plants to inhibit powdery mildew infection.