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Mildew Disease of Lawns

Powdery mildew of bluegrass is a common lawn disease some years, particularly in fall. It is easy to identify because of the white powdery fungal growth that covers the grass blades. Shady lawns, or turf areas on the north side of houses, are much more likely to become infected or damaged by the disease than sunny locations.

Some turf varieties, particularly Merion, are more susceptible to the disease than other varieties. For this reason, powdery mildew is likely to damage susceptible varieties growing in shady areas. In severe cases the lawn turns yellow and may thin out. It is also subject to winter injury.

Consider your lawn situation before deciding what control action to take with powdery mildew. If you are just starting a lawn and you know the area will be shady, avoid varieties that are vulnerable to the disease.

Red fescue is the most shade tolerant grass available. The Nugget, Glade and other Kentucky bluegrass varieties reportedly have some shade tolerance. These grasses can also be used to overseed the shady areas of lawns, but you should get advice on good ways to establish an overseeding. It is not easy to accomplish. For those sunny lawns that become only occasionally infected, especially late in the fall, there is really no need for treatment. The powdery mildew will not hurt the lawn.

In some situations it may be desirable to treat the disease with a fungicide to protect the lawn and improve its appearance. We have had the best success with Benlate and Tersan 1991. Be sure to follow label directions.

If you have further questions, please contact your county office of the NDSU Extension Service.

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