Weather conditions in many parts of Illinois have been conducive to the development of brown patch on turf. This fungal disease is caused by a Rhizoctonia species. It commonly occurs in hot, muggy weather when night temperatures are at least 70°F and daytime temperatures are in the 80s and 90s. It is favored by heavy rains or watering and by grass that is dense and at least adequately fertilized.
Brown patch is easier to diagnose in the field than in the lab. Symptoms usually stand out most vividly in hot, moist, overcast weather. The disease appears in patches, up to 2 or 3 feet across. These patches may be dark blue initially, as though turf is under drought stress. The color quickly changes to purple-brown, then light brown. Patches may develop green centers and resemble summer patch and necrotic ring spot. In light infections, the turf generally recovers in 2 or 3 weeks. When the attack is severe, the crowns, rhizomes, stolons, and roots may turn brown and rot, causing turf to be thinned or killed in large areas.
Brown patch can be prevented by using cultural practices listed in Report on Plant Disease No. 411. If the disease occurs, chemicals may keep it from spreading, but long-term control requires following cultural recommendations. Chemical options are listed in the Illinois Commercial Landscape & Turfgrass Pest Management Handbook or the Illinois Homeowners’ Guide to Pest Management. Read the label on the product for recommended formulation, rates, and timing for your turf conditions. Because such applications usually require sprays at 5- to 14-day intervals throughout the summer, fungicide control of brown patch is usually reserved for golf courses. Products are not always available in quantities suitable for homeowner use. For a severe infection in a home lawn, rake and remove the dead areas, follow cultural recommendations in the Report on Plant Disease and re-seed with a blend of resistant turf grasses suitable for the light requirements of the lawn.