Problem: Summer Patch
Summer patch usually occurs from June through September, when hot, dry weather follows a wet period. The disease is caused by a fungus (Magenporthe poae) that infects the roots during cool weather (60° to 65°F), usually in late spring. When hot weather arrives, the roots cannot provide enough water, and the top dies. Summer patch is most prevalent in compacted soils and lawns with excessive thatch buildup, especially on exposed sites and steep slopes. It is worsened by infrequent watering and excessive nitrogen applications. It can affect many types of lawn grasses, including bentgrass, Kentucky and annual bluegrass, and fescue-especially when cultivars are unsuitable for local conditions. The symptoms of necrotic ring spot are so similar to those of summer patch that the two diseases cannot readily be distinguished outside the laboratory.
Summer patch usually occurs from June through September, when hot, dry weather follows a wet period. Dethatching and regular aeration help prevent summer patch, as do frequent, light waterings and regular but light applications of nitrogen. Reseed seriously affected areas with appropriate grasses.