Photo by Ali Harivandi

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Hosts

Annual bluegrass (a common weed in turf), Kentucky bluegrass

Symptoms

Infected leaves, sheaths and stems have circular to elongated brownish spots with brown centers and dark brown or purple borders. Crowns and roots have a dark brown rot. Symptoms may occur throughout the lawn rather than in clumped areas. Plants may die in hot, windy weather, leaving thinned areas throughout the turf.

Conditions favoring disease

Warm temperatures (70° to 90°F) and high humidity favor the development of leaf spot. Weakened turf may be the result of poor cultural practices. Mowing too short and applying high amounts of nitrogen contribute to the development of the disease.

Prevention and management

Reduce shade and improve soil aeration and water drainage. Follow the recommended irrigation requirements for your turf species and avoid excess nitrogen fertilizer. Maintain as high a mowing cut as possible. Fungicides are available but usually are not warranted for the home lawn.

For more information on lawn diseases, refer to:
Pest Notes: Lawn Diseases: Prevention and Management