Managing Summer Lawn Diseases (6-20-11)

We encounter most turf diseases in home lawns during the spring when temperatures are moderating and afternoon showers are frequent. However, our summer days can also present some turf disease problems. Gray Leaf Spot (Piricularia grisea) of St. Augustinegrass can cause severe thinning of home lawns during the heat of summer. This disease is more common during extended periods of hot, humid weather. Although primarily a disease of St. Augustinegrass, it is also found on crabgrass and occasionally on centipedegrass.

Infected turf will have irregular gray, dirty-yellow or ash-colored spots with brown, purple, or water-soaked borders on leaf blades. The disease is usually noticed first in shaded areas that remain damp. Under heavy disease development, the grass may have a burned or scorched appearance resulting in death or severe spotting of the leaf blades. Fungus spores are carried by the wind, splashed rain, irrigation water, and mowers to sites for new infection. Seldom will this disease kill an entire lawn but can thin it severely enough to be unsightly and encourage weed infestations.

Control is best accomplished by avoiding excessive nitrogen fertilization. Water early into the day so foliage will dry and not remain wet overnight. Mow with a sharp mower when the turf is dry. There are several fungicides that are effective on this disease when applied at 10 day intervals during periods of favorable infection.

Dollar Spot (Sclerotinia homoecarpa) is a common summer diseases found on many turf species but is most common on Bermudagrass. This disease is found more prevalent on neglected turf or areas that are under moisture or nutritional stress caused by the lack of nitrogen. Warm humid weather with heavy dew promotes the disease, which begins as small (2-3 inch) circular dead spots throughout the lawn. These small spots can then grow together to form much larger blighted turf. Fungicides are effective in controlling dollar spot but a good fertilization and watering program will also help in the management of this disease.

Published June 20, 2011

Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. wwells@ext.msstate.edu