The frequent spring rains in many parts of Illinois have prompted growth of slime molds. The funguslike slime molds prefer warm, moist conditions. Look for them on bark mulches, on wood chips in play areas, on low-lying objects, or growing on any object that can be used as a perch. We usually see species of Physarum, Fuligo, and Stemonitis.
Although slime molds cause much concern to the homeowner, they do not absorb nutrients from live plant material. They feed on decaying organic matter, fungi, and bacteria in the soil and the turfgrass thatch layer. Even bark mulches decompose and produce materials that the slime molds “consume.” The slimy, amoeba-like stage 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, or driveways, or over vegetation such as turfgrasses, strawberries, flowers, ground covers, weeds, and the base of woody plants.
Most gardeners want to know what to put on slime molds to kill them. Chemicals do not provide control. Instead, for abundant molds, remove the spore masses in a plastic bag and break up the remaining masses by vigorous raking or brushing. Although some like to hose down the spores with a stream of water, keep in mind that water can also spread the problem by spreading around the swimming spores. Raking affected mulch or wood chips helps the area dry out more quickly. Mowing the lawn usually removes the spore masses in turfgrasses. For more information about slime molds, read Report on Plant Disease, no. 401, “Slime Molds of Turfgrass.” The publication is available in Illinois Extension offices or at http://www.ag.uiuc.edu/%7Evista/ and then clicking on publications, horticulture. The publications are listed alphabetically. An excellent site with images of slime molds is by a Wisconsin mycologist and is at http://botit.botany.wisc.edu/toms_fungi/june99.html.