Rhizoctonia solani, the fungal pathogen called brown patch, is a foliar disease that does not damage the crown or roots of the grass plant. According to Ohio State University, brown patch is capable of infecting and killing most major cultivated turfgrass species. Mild outbreaks cause unsightly brown patches in the lawn.
According to the University of Florida Extension, brown patch is most likely to strike between November and May, when temperatures are below 80 degrees. The fungus attacks the weakened leaves of the grass. The pathogens become active during the summer heat, says Purdue University, when night temperatures stay above 65 degrees Fahrenheit.
According to Ohio State University, brown patch symptoms will vary greatly among turfgrass species, the mowing height, soil and environmental conditions. In low-cut grass, patches of brown grass will appear anywhere from a few inches to 2 feet. In higher cut turfgrass species, irregular circular patches will appear from 2 to 3 feet, with thinning occurring as well. Leaf lesions also appear gray and lumpy.
Avoid brown patch by using disease-resistant varieties. Although all cool-season turfgrass varieties are susceptible to the disease, some are more resistant than others. Kentucky bluegrass has a higher resistance than many varieties. Ohio State University suggests several moderately resistance ryegrasses, tall fescue varieties and Kentucky bluegrass.
Excessive use of nitrogen fertilizer encourages the development of brown patch, especially when applied in humid and warm environments. Keeping foliage as dry as possible and avoiding over-watering prevents the spreading of the fungal pathogen. Irrigation is best done in the morning. Core aeration to improve drainage and air circulation lowers infection rates.
According to Purdue University, several selective fungicides are available for the management of brown patch. Strobilurin carrying products are very effective on brown patch. Fungicides are applied according to the direction on the label.