Superficial, white, powdery patches of mildew develop on grass leaves. Heavily infected turf appears dull white, as if dusted with flour. When damage is severe, powdery mildew may kill plants, especially in new plantings in the shade.
Powdery mildew is common in the spring and autumn when the nights are damp and cool and the days are mild and cloudy. Races of the fungus are specialized, infecting only certain varieties of certain turfgrass species. High-nitrogen fertilizers cause dense growth of the grass and create an ideal environment for the mildew fungus. Powdery mildew is much more severe in shaded areas where air circulation is reduced.
Where shade is dense, grow a shade-tolerant ground cover.Grow fine-leaved fescue or rough bluegrass in moderate shade. Shade-tolerant (and, if available, powdery-mildew resistant) varieties of Kentucky bluegrass and other species will do well in shady, open areas. In mildew-prone areas, mow relatively high and water and fertilize as appropriate to promote vigorous, but not lush, growth. On high-value turf, where powdery mildew consistently reoccurs, a fungicide program may be economically feasible. Two or more applications of a suggested fungicide spaced 7 to 21 days apart should keep the disease in check.