Powdery mildews generally present more serious problems to cereals and forage grasses than turf grass. At times, however, powdery mildew can damage your turfs density and aesthetic beauty, especially on shaded areas of susceptible Merion Kentucky bluegrass.
The disease appears first as small, superficial patches of ugly white to gray-white fungus growth on the leaves and sheaths. The growth occurs mainly on the upper surface of the leaf, but it may eventually engulf the entire leaf. Once the fungus penetrates your grass, a yellow lesion develops, later turning tan or brown as the vitality of your lawn is killed. In advance stages, older, lower leaves are often completely covered by mildew. In severely infected areas, the turf is a dull, pale white, as if dusted with lime.
Powdery mildew prefers cool, humid, cloudy weather, with temperatures about 65 F. The mildew occurs in severe form during the late fall and early spring.