University of Maryland Extension

Powdery Mildew - Lawns

white powdery coating on grass blades

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Powdery mildew is a common fungal disease of blue and fescue grasses grown in the shade that causes a white powdery appearance on the blades.

Grasses Affected:

· Grasses infected typically include Kentucky bluegrass, bermudagrass, fine-leafed fescues and zoysiagrass.

Primary symptoms:

· The initial symptoms begin as small patches of white to gray dusty growth on the leaves and sheaths of shade grown grasses. These patches quickly enlarge and spread often completely covering the affected grasses.
· Affected areas may appear as though dusted with lime or flour. Older leaves are often more severely affected than younger leaves.
· Infected plants will often succumb to other problems such as drought and low temperatures. The infected blades gradually turn from green to tan to brown as they die.

Season: Powdery mildew is more common in the spring and fall because the infection is favored by cool humid conditions.

Environmental Conditions: Cool, humid, cloudy periods are conducive to infection.

Management:

· Select shade tolerant grass cultivars when establishing turf.
· Improve sunlight and air circulation where possible by pruning or removal of surrounding trees and shrubs.
· Mow at the turf at the highest recommended height and avoid other stresses such as drought and low fertility.

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