Summer Patch of Turfgrasses Plant Pathology Summer Patch of Turfgrasses Summer patch has been showing up on Iowa lawns for the last 2-3 weeks. This disease is one of the most damaging problems of turfgrasses and sometimes one of the most frustrating to control. Summer patch is caused by a fungus, Magnaporthe poae , which lives in the soil and attacks the roots. Symptoms can proliferate in a lawn to the point where some areas have more damage than healthy lawn. A similar disease, called necrotic ring spot, produces identical symptoms in fall and spring, but summer patch typically appears in late June and July.
Experience indicates that summer patch is by far the more common problem in Iowa.
Scenarios for outbreaks of severe summer patch often have certain elements in common. The roots of the sod on the clay soil are often very slow to penetrate the tough, poorly oxygenated clay, so they don't extend deeply. In the sands and gravel, the entire soil profile dries out rapidly due to its high porosity. These weakened roots are easy prey for the summer patch fungus. Management of summer patch starts with good cultural practices.