We have been seeing cases of brown patch in home lawns lately, including my own. Weather conditions in many parts of Illinois have been conducive to its development. This fungal disease is caused by a Rhizoctonia species. It commonly occurs in hot, muggy weather when night temperatures are at least 70oF 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 as patches, up to 2 or 3 feet across. The patches may be a dark blue color initially, as though under drought stress. The color quickly changes to purple-brown and then light brown. The 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.
Cultural practices for brown patch are listed in Report on Plant Disease (RPD) no. 411,"Rhizoctonia Diseases of Turfgrasses," available on the VISTA Web site or in Extension offices. Once the disease occurs, chemicals may keep it from spreading, but long-term control requires following cultural recommendations. Chemical options are listed in the Commercial Landscape and Turfgrass Pest Management Handbook or the Home, Yard, and Garden Pest Guide. Read the label on the selected product for recommended formu-lation, rates, and timing for your particular 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 RPD, and re-seed with a blend of resistant turf grasses suitable for the light requirements of the lawn. Now is a great time to get out there and do the raking and seeding.