Afternoon summer showers may flair dollar spot 06-18-07

Afternoon summer showers may flair dollar spot

Overnight leaf wetness from evening showers or late afternoon irrigation may stimulate an outbreak of Sclerotinia homeocarpa, better known as dollar spot.

Dollar spot is a common fungal disease that attacks most warm season turf species, but most severe on bermudagrass and zoysia. It occurs when temperatures are between 50 – 95 degrees with high relative humidity or extended periods of leaf wetness. The disease is most severe when the turf is growing slowly, either from entering or leaving dormancy, summer stress, or from nutritional deficiency particularly the lack of nitrogen.

Early symptoms on individual leaves are chlorotic (yellow) areas that become water-soaked and later turn a bleached straw color. The fungus generally appears as small, circular spots about the size of an old silver dollar, thus the name dollar spot, even though these spots can be as large as two to eight inches in diameter.

During early morning hours when dew is present, you may observe the fungal growth on top of the turf leaf blades that resemble tiny spider webs. Upon close examination the spider webs will have a hole in the center of the web and the tiny threads will be spun in a circular pattern. The fungal mycelium growth will disappear as the dew dries and the turf leaf blades will begin to turn yellow.

Prevention is the best control of this disease. Good cultural practices include maintaining adequate soil moisture, adequate nutrition particularly nitrogen, mow regularly and maintain correct mowing height, prevent thatch buildup, water early enough in the day to reduce overnight leaf wetness, and apply appropriate fungicides if disease becomes severe.

More detailed information on this and other turf diseases can be found on the Extension Service Web site.

Published June 18, 2007

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