Brown patch is the most serious and frequently occurring disease of tall fescue.
The lawn may have a uniform brown appearance without distinct patches from the disease by the end of the summer. Lesions that are olive color in the morning when dew is present, or during rainy weather, develop rapidly on young leaves. As the tissue dries the lesions become light tan. Webby mycelium of the fungus may be seen on the lesions and the surrounding grass blades in very humid weather. Vigorously growing plants that have received higher than recommended rates of nitrogen fertilizer during the spring or the summer are very susceptible to the disease.