Under the most favorable conditions it can kill a stand within 24 hours. A few of the species that cause this disease are favored by cooler weather and are found more commonly in spring. The spots usually appear in clusters. They may grow very fast and are usually larger on lawn grasses than on golf greens. Patches often grow together and their spread may follow the direction of mower movement.
Patches are dark at first, then fade to a tan to reddish-brown color.
When they are first infected, leaves are water-soaked, dark and slimy in the early morning . When they dry, they become reddish brown, then tan and shriveled. If the humidity is high, the patches may become covered with fluffy, white, fungal growth. When weather is less favorable, the leaves at the edges of the patches may have distinct white or straw-colored spots or bands on the blades. The edges of these spots or bands are the same color as the centers.