Powdery mildew of Crucifers

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. Additional signs of the pathogen would be that its conidia are singly produced (not in chains) and are ovoid to cylindrical in shape, ranging from 42.5–57 µm × 14.5–20.5 µm in size. Also, E. cruciferarum has rather variable appressoria, differing from lobed to simple, and haustoria that are multilobed. 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. Colonies may be gray and restricted in size on resistant cultivars as the host reaction produces black speckling beneath the colony. On Brussels sprout, gray or purple symptoms occur on the stems, while on the sprouts there may be white colonies or fine black speckling in radiating lines.
Disease diagnosis is determined on the basis of anamorph morphology and host.