Generally, slime molds are not prevalent in the Midwest until midsummer when temperatures and humidity are high. Reports of slime molds invading gardens have begun to occur in Illinois and it is May! We can attribute this phenomenon to odd weather.
Although these organisms cause much concern to the homeowner, slime molds do not take nutrients from the plant material. They feed on decaying organic matter, fungi, and bacteria in the soil and the turfgrass thatch layer. We often see them on bark mulches or on wood chips in play areas. During warm, moist weather, the slimy, amoeba-like stage appears on low-lying objects and may be watery-white, gray, cream to light yellow, violet, blue, green, or purple-brown greasy masses as large as 1 to 2 feet in diameter. This stage soon develops into colorful crusty fruiting bodies filled with masses of dusty spores. Slime molds are primitive organisms that flow (too slowly to watch) over low-lying objects such as mulches, sidewalks, driveways, or over vegetation such as turfgrasses, strawberries, flowers, ground covers, weeds, and the bases of woody plants.
Most gardeners want to know what to put on these molds to kill them. Chemicals do not provide control. For abundant molds, remove the spore masses in a plastic bag, and break up the remaining masses by vigorous raking, brushing, or hosing down with a stream of water. Mowing the lawn usually removes the spore masses in turfgrasses. For more information, read RPD No. 401, which discusses slime molds in turf. It is also available on the Vista Web site listed previously.