Brown patch, caused by the fungus Rhizoctonia solani, is common on tall fescue during the summer. The fungus becomes highly active when conditions are moist and night temperatures are above 65
degrees F. 
That is, if you step outside in the morning and the lawn is dewy with air temperatures 65-75 then conditions are favorable for brown patch. Brown patch symptoms develop in 24-48 hours during warm, humid weather. Patches initially are dark purple-green, but then quickly fade to light tan or brown as the diseased leaves dry out. Diseased turf may appear drought stressed even when the soil is moist. The pattern of damage is variable. Damaged areas sometimes form circular patches of blighted turf from several inches to several feet in diameter. However, damage often develops in a more irregular pattern without formation of circular patches. The pathogen mostly infects the foliage and makes lesions with a brown border, and the leaves in affected areas are killed. Changes in the weather or applications of fungicides will slow down the pathogen, new leaves will emerge, and the turf will recover in 2-4 weeks. In extreme cases the pathogen can infect crowns or stems, leaving weak areas of turf that are susceptible to invasion by weeds. Irrigation is the most important factor to manage. This disease is favored by long periods of leaf wetness. Do not irrigate in the evening—this leads to a long, wet period overnight that extends into the dew period in the morning. Water in the morning instead. Please call the office and we will give you a quote to treat the Brown Patch with a fungicide.