Summer patch is a kind of disease that affects some species of turfgrass, particularly the Poa pratensis or the Kentucky bluegrass, the Poa annua or the Annual bluegrass, and some species of the Festuca genus. It is also known as the Poa patch, most likely in reference to the genus of grasses it often affects. The disease often appears as circular or crescent spots of pale, dry grass that eventually die if left untreated, resulting in bald spots. In Annual bluegrass, the disease has a “frog-eye” feature, having a small patch of green grass in the middle of the straw-colored ring of grass. Some grass-covered venues that can acquire summer patch include golf courses, sports fields, and house lawns.
The primary cause of summer patch is a type of fungus called the “Magnaporthe poae.” The fungus is commonly found in the soil and does not really attack the grass until the appearance of some external factors, one of which is the hot weather. Magnaporthe poae specifically damages the roots of the plants, and creates dark strands called hyphae, which can be microscopically seen. If observed by the naked eye, plants that are infected with summer patch will exhibit thin and fewer root strands, which look necrotic or dead.
As the name implies, summer patch is prevalent during the summer season from the months of June to September. This is because the high temperature prevents already-infected roots from sustaining the grass and providing it with enough water. Soil that have temperatures ranging from 65 to 70°F (around 18 to 21°C) is susceptible to the fungus, especially when the aerial temperature is around 90%deg;F (around 32%deg;C) or hotter. Fungi often thrive in moist and humid places, so lands that are regularly maintained and watered, such as golf courses and designed landscapes, are more at risk of acquiring the Poa patch. Other factors that encourage the disease are insufficient drainage, lack of air circulation, and if the soil is heavily compressed.
To prevent summer patch or to stop it from further infecting the grass, the soil must maintain a pH ranging from 6.0 to 6.5, as the slightly acidic pH is not favorable for the fungus. This can be done by nourishing the soil with some nitrogen. Frequency and amount of watering should also be lessened, and a drainage system can also be installed to release excessive moisture. If possible, the soil can be plowed to reduce compaction and to introduce proper air circulation. Fungicides can also be used if the summer patch has already spread, although it is more effective as a preventative tool.