Spider webs or dollar spot? (8-31-09)

During early morning hours, when dew is present, you may observe on your lawn small circular patches of fungal growth on top of the leaf blades that resemble tiny spider webs.

Upon close examination, 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 of Sclerotinia homeocarpa, better known as dollar spot, will disappear as the dew dries and the turf leaf blades will begin to turn yellow.

Overnight leaf wetness from evening showers, late afternoon irrigation, or early dew formation may stimulate an outbreak of dollar spot. This fungal disease attacks most warm season turf species, but is most common on bermudagrass and zoysia. 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.

It occurs when temperatures are between 50 – 95 degrees with high relative humidity or extended periods of leaf wetness. 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 2-8 inches in diameter.

Prevention is the best control of this disease. Good cultural practices including 1) maintaining adequate soil moisture, 2) adequate nutrition particularly nitrogen, 3) mow regularly and maintain correct mowing height, 4) prevent thatch buildup, 5) water early enough in the day to reduce overnight leaf wetness, 6) apply appropriate fungicides if disease becomes severe.

Published August 31, 2009

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. [email protected]