Photo by Ali Harivandi

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Hosts

Annual bluegrass (a common weed in turf), Kentucky bluegrass, St. Augustinegrass, tall fescue

Symptoms

Rhizoctonia blight first appears as irregular patches of weakened grass that may enlarge to many feet in diameter. The affected area may be a smoky color. Leaves and sheaths are watersoaked, wilted, and light brown. Fungal threads may be apparent.

Conditions favoring disease

High temperatures (80° to 95°F) and high humidity favor the development of Rhizoctonia blight. Excess thatch, poor drainage, and soft, lush growth due to excessive nitrogen also contribute to disease development.

Prevention and management

Reduce shading and improve soil aeration and water drainage. Follow the irrigation and fertilization rates for your turf species. Avoid watering in the evening. Dethatch when the thatch layer exceeds 1/2 inch (1.2 cm). A fungicide may be useful if the disease was severe in the past or for seedlings in young turf.

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