Slime molds may appear in maintained turfgrass as well as in ornamental planting beds.
Watery white, gray, black, or cream-to-yellow, slimy masses grow over the grass blades (or mulch or other surface) in round to irregular patches. The masses soon dry to form bluish gray, grayish white, black, white, or yellow powdery growths that are easily rubbed off. The grass blades beneath are healthy or somewhat yellow after being shaded.
Slime molds are harmless organisms that suddenly appear during warm to hot weather following heavy rains or watering. These primitive organisms feed on decaying organic matter, fungi, and bacteria in the thatch and soil. Slime molds do little damage to living turfgrass but may cause some yellowing by shading the affected leaves. Fruiting of the slime molds is favored by warm, moist weather and thick thatch.
Slime molds soon disappear when left alone. You can accelerate the process by raking, brushing, or mowing the area. After the onset of dry weather, you can hose down the area with water.