Bermuda grass (Cynodon spp.) is a popular turf grass throughout the southeastern United States. A warm-season grass at its best during the dog days of July and August, Bermuda grass has deep, vigorously spreading roots and lush, green foliage. Its major drawback is susceptibility to several pests and diseases. A common problem is slime mold. In its final stages, this mold can cover the grass with large patches of black powder.
Slime Mold Cause
Slime molds belong to the Mucilago, Fuligo and Physarum genera. Physarum slime molds are the most likely to attack Bermuda grass, says assistant professor and urban plant pathologist Stephen Vann of the University of Arkansas Cooperative Extension. These molds are single-celled organisms with millions of nuclei. They crawl across the grass at a rate of 1 inch per day in search of decaying plant material to eat.
What Slime Mold Does
Slime molds feed on germs and decaying organic material. They use the green blades of Bermuda grass to support themselves as they consume the layer of dying thatch beneath. The molds creep up the blades of grass that are wet from fall or dew, where they dry into crusts. They also cover organic mulches and low ornamental plants, says Auburn University professor and plant pathologist Dr. Austin Hagan in a report written for the Alabama Cooperative Extension.
Symptoms of Infestation
New infestations give grass a slimy appearance. Most affected lawns have scattered mold patches, each of which can be several inches to 1 foot in diameter. Early stage mold resembles animal vomit. It can be one of several colors, including white, gray, yellow or purple. Dried mold encrusts the grass with dark gray or black spore capsules. The spore capsules continue to deteriorate for up to a week, when they release a powdery, spore-filled material that gives grass a sooty appearance.
While the molds don't feed directly on Bermuda grass, severe infestations can shade the turf, decreasing photosynthesis and causing leaf yellowing. Some slime molds that spread to mulches may produce toxic toadstools.
While slime mold is unappealing, it seldom harms lawns enough to require fungicidal application. Wait until your Bermuda grass is dry before raking or sweeping the mold from the affected areas. Use a garden hose to wash the black spores from the grass.When slime molds occur in the lawn, rake or sweep the thatch when the grass is dry. Avoid washing it away in damp weather, because the spores may re-establish mold in a new patch of wet grass.
Slime mold spores can spread by contact with pets, shoes and clothing.