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Powdery mildew in the home lawn

Jill Pokorny

Powdery mildew, caused by the fungus Erysiphe graminis, is a common disease of Kentucky bluegrass and fescue. The fungus survives winter in infected plant material and produces spores throughout the growing season, which are rain splashed or wind blown to susceptible grass blades. Infected leaves are covered with a dusty, powdery white to gray fungal coating, which can be rubbed off with fingers. The grass often looks as if it has been dusted with flour or lime. Heavily infected leaves may turn yellow and die, causing areas of turf to thin.

Powdery mildew is most severe in the spring and autumn, when temperatures are cool and humidity levels are high. It most commonly occurs in shaded areas where air circulation is poor. Since a specialized environment is essential to the development and spread of powdery mildew, modifying the environment can help control this disease. Many areas in established lawns can be opened up to light and air with minor tree and shrub pruning. Similarly, when landscaping a new area, space your plantings to avoid heavy shading and poor air circulation. Plant shade tolerant and resistant grass varieties whenever possible. Properly water, fertilize, and dethatch to maintain a healthy lawn. Overwatering and fertilizing can stimulate powdery mildew. Chemical control is not usually recommended for home lawns. However, in severe cases Bayleton may be applied at the first sign of disease.

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