The powdery mildew fungus is made up of different races and forms that are highly specialized, even down to the cultivar of wheat or barley they can attack. Wheat cultivars might be resistant to a certain race of the mildew fungus, but susceptible to another race. This 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 abundantly on the white mildew that covers the surface of infected plant parts.
Development is rapid in warm humid weather.
This fungus is unique in that spore production and infection can take place in the absence of free moisture. Heavy rains are not favorable to spore production or fungal growth over the leaf surface. Rapid growth and dense foliar canopies caused by high nitrogen fertilizer application encourage disease development. Damage Description 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.