Bermuda grass (Cynodon spp.) creates a vigorous, dense turf that resists drought, wear and salt. Its vigorous, spreading habit contributes to rapid thatch accumulation, which interferes with air and water movement and harbors various pests and diseases. Excellent cultural care can slow thatch accumulation and helps to prevent or address diseases like powdery mildew.
Powdery Mildew on Bermuda Grass
Powdery mildew first appears on a Bermuda grass lawn as isolated tufts of grayish to white powdery growth on upper leaf surfaces. As the disease progresses, the fungal growth becomes denser, making individual grass blades look as though they are coated with flour. Patches of the turf develop a dull white appearance. Grass blades covered with the white growth may turn yellow and wither and large areas of infected lawn may develop a thin look.
About the Disease
Powdery mildew on Bermuda grass is caused by a fungal pathogen. This pathogen overwinters in debris as specialized structures or in dormant, infected grass. Spores spread by wind and prefer to infect grass when humidity is high but there is no free water on the grass blades. Temperatures around 65 degrees Fahrenheit, shady conditions and poor air circulation encourage powdery mildew establishment and spread. Direct sunlight hitting the turf or hot leaf temperatures can kill this pathogen. Because Bermuda grass grows in U.S. Department of Agriculture plant hardiness zones 7 through 10, warm summers are likely.
Control and Prevention
Powdery mildew growing on the Bermuda grass will not infect other plants and isn't a health threat to children or pets. You can usually control powdery mildew with cultural methods and you shouldn't need to use chemicals. Prune overhanging branches and thin out branches on nearby trees, shrubs and plants to increase the amount of sun hitting the turf and improve air circulation around the grass. Mow the Bermuda grass to 1 1/2 inches and avoid excessive nitrogen fertilizer applications. In shady areas, consider overseeding the Bermuda grass with a shade-tolerant species or cultivar or replacing the lawn with a ground cover or mulch.
Other Possible Diseases
Although powdery mildew is likely responsible for powdery gray growth on Bermuda grass, other fungal diseases could cause similar symptoms. Dollar spot appears as small, circular spots no more than 5 inches in diameter. Grass blades look water-soaked or brown, sometimes with a reddish band, and whitish, cobwebby growth may appear on the grass in the early morning. Gray snow mold, which appears in spring after snow melt, causes grayish or white circles that become straw-colored dead spots. The infected grass may be covered by a fluffy white growth that is speckled with dark-colored fruiting bodies. Slime molds show up as slimy masses -- which may look like vomit -- in varied colors, but this form is both preceded and followed by spore masses that are gray, black, white or another color. Slime molds do not directly injure the grass, as they feed on dead organic matter, fungi and bacteria, but they may interfere with photosynthesis and cause a yellowing of grass blades.