Photo by Eric B. Nelson, Cornell University

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Hosts

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

Symptoms

Summer patch appears as circular yellow or tan areas of dead and dying plants up to 1 foot (30 cm) in diameter. Healthy green plants may remain in the center. Dark brown or black fungal hyphae develop on roots, crowns, or stolons. Vascular discoloration may occur in later stages of the disease.

Conditions favoring disease

High temperatures (85° to 95°F) in the late spring favor the development of summer patch. The disease is most severe when the turf is mowed low or when there is excessive soil moisture.

Prevention and management

Promote root growth by soil aeration and slow-release nitrogen. Improve drainage, reduce compaction, control thatch, and avoid drought stress. Follow irrigation recommendations for your turf species. Mow at the higher end of the recommended height range for your species. Reduce your soil pH if it is higher than 7. A professional soil analysis may be necessary to determine which nutrients are lacking in your soil and can provide you with information about what to add to your soil to maintain an ideal soil pH.

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