Brown patch appears as irregularly shaped enlarging patches of blighted turf grass, a few inches to 2 feet in diameter. At first, it's purplish-gray, but then fades to light brown as the withered leaves of your lawn dry out and die. During periods of warm, humid weather, dark purplish rings bordering the diseased area can be seen early in the morning.
The fungus begins to be active when the average daily air temperature is 73°F. When temperatures reach 80° to 85°F, particularly in a moisture-saturated atmosphere, Brown Patch symptoms can become quite severe within hours.
The disease may even occur under conditions of low soil-moisture content, but a moisture-saturated atmosphere will cause a Brown Patch outbreak in epidemic proportions, threatening large areas of your lawn. On leaves that are already infected, the disease will have an active growth in the 80° to 85° temperature range.