Pythium Blight and Zoysia

Preventive Care

• Properly maintaining your zoysiagrass is essential to prevent and control pythium blight. Grow zoysiagrass in areas that are exposed to full sun to partial shade; if you plant the grass in the shade, its growth may become sparse. Maintain moist, well-drained soil with an acid to neutral pH of 6.0 to 7.0. For best results, keep the lawn mowed to a height of 1 inch and irrigate in the morning when the grass is dry; water to a depth of 4 to 6 inches.

Disease

• Pythium blight is a disease that affects a wide variety of turf grasses, including zoysiagrass. Caused primarily by the fungal pathogen Pythium aphanidermatum, this disease is also referred to as "cottony blight" or "grease spot." Blight is most active during periods of hot, humid weather and its development is encouraged by the moistness of poorly drained soil. Other contributing factors include a nighttime temperature that exceeds 68 degrees Fahrenheit and rainfall, explains the University of Arkansas Cooperative Extension Service.

Effects

• As one of its nicknames -- water mold -- suggests, pythium blight often results in dark grass blades that appear to be saturated with water; the spots feel greasy to the touch. Areas of grass up to 12 inches wide may take on this greasy appearance. These areas then become red, brown or gray as the disease progresses and the grass dies. Another moniker, cottony blight, comes from the formation of a cotton-like mold that often develops over dead patches of grass.

Solutions

• Before you employ control measures, ensure that the disease is pythium blight by testing grass with an enzyme-linked immunosorbent assay (ELISA) kit. To manage blight on zoysiagrass, prevent its formation by dethatching at the beginning of summer and maintain a thatch thickness that remains under 1/2 inch. Improve drainage, if necessary, by core aerating the soil. Use slow-release nitrogen fertilizers to avoid overfertilizing, which results in excessive growth that promotes the development of disease. Because applying fungicides for this issue should be performed by professionals and must be preventive, and because chemical control is typically a "last resort," explains the University of Arkansas Cooperative Extension Service, focus on cultural care so your lawn can heal.