Summer Patch, caused by the fungus Magnaporthe poae, is less common on Kentucky bluegrass. It is a disease that occurs during the hot portion of the summer. The initial symptoms are yellow patches 6-12 inches in diameter. The turf in these patches thins and the remaining turf turns bronze in color. If warm weather continues, all of the turf in the patch may die. The dead patches may be colonized by weedy grasses.
Soil moisture is important in disease development. Excess irrigation or an absence of irrigation during hot weather may make the disease more severe.