Slime molds are primitive organism that exhibit characteristics of both plants and animals, although they are considered fungi. Numerous species of slime mold occur on turf; the most common is Physarum cinereum. Slime molds are not pathogens and cause little more than some yellowing.
Slime molds grow on the surface of leaves and stems feeding on decaying organic litter and on other fungi and bacteria in the thatch layer in the soil. They often appear on well-maintained turf after a warm summer rain and usually reappear in the same area year after year and last one to two weeks. Slime mold spores are spread by wind, water, mowing, and other activities on the turf.
A slime mold is composed of thousands of tiny, usually purple, gray, white, or cream, sack-like spore enclosures called fruiting bodies. These form in 4- to 6-inch patches in the turf and may be widely spread or clustered into groups. The slimy growth is called a plasmodium. This dries into a powdery mass of spore-bearing bodies that coat the grass blades.
Slime molds are more of a curiosity or nuisances than a threat to the turf. Control measures are usually not necessary; but if desired, slime mold can be removed by vigorous raking, mowing, or hosing down with a fast stream of water.
J.E. Watkins. (1997). Diseases of Cool Season Turfgrass. In F. Baxendale, Ph.D., & R. Gaussoin, Ph.D., Integrated Turfgrass Management for the Northern Great Plains (pp. 138-139). Location: Nebraska