Fungus overwinters on crop residue. Spores are dispersed in early spring by wind and infect susceptible plants. Secondary infections within the crop result from spores produced on the white mildew that covers the surface of infected plant parts. Disease develops rapidly in warm, humid weather. Spores can germinate even in the absence of free moisture on leaf surfaces. Heavy rains do not favour spore production or fungal growth over the leaf surface. Rapid growth and dense foliar canopies such as those caused by high nitrogen fertilizer application encourage disease development.
Powdery mildew attacks the leaves, but stems and heads are also affected. The fungus grows primarily on the surface of the host and feeds on the living green cells of the cereal plant. Small white or gray tufts of spore-producing fungus are most prevalent early in the growing season on the upper surface of the lower leaves. Tissue on the opposite sides of the leaf turns pale green to yellow.
The fungal tufts enlarge, join and may turn reddish brown. Later, this fungal growth becomes dotted with black pepper-like reproductive bodies that enable the fungus to survive between growing seasons. Plants that become infected early may be stunted and fail to head where infection is severe.
Choose resistant cultivars.
Apply a foliar fungicide.
Balance fertilizer application.