Powdery mildew is a fungal disease affecting the leaf blades. Bluegrasses and fescues are the most commonly affected lawn grasses. Blades and sheaths of older leaves are covered with mats of fine, white or grayish fungal mycelia on the upper surfaces. Under favorable conditions, the fungus can spread rapidly and become quite dense. Infected leaves turn yellow, then tan to brown, and die back. Severe infections can kill grass plants or can weaken them to such a degree that other factors such as cold can kill the plants. Conditions favoring disease development include cool, humid, cloudy weather and heavily shaded lawns. The fungus survives primarily in infected plants.

Management Options

Non-Chemical Management

When using Kentucky bluegrass, plant mixtures of improved varieties.
Do not plant grass in heavily shaded areas.
When practical, prune trees and shrubs to reduce shading and improve air circulation.
Provide proper culture, including adequate, balanced fertilization and deep, infrequent watering.
Water grass in the morning so it can dry quickly.
Mow grass regularly at the recommended height.
For more information on proper care of lawns, including mowing heights and fertilizer recommendations, see EB0482E, Home Lawns.

Select non-chemical management options as your first choice!

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

Not recommended for home lawns.

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Caption: Powdery mildew Photo by: R.S. Byther

WSU Extension

Hortsense