A few calls concerning slime molds have been received at the Plant Clinic. With the continuation of warm, wet weather that favors growth of slime molds, more calls are expected. Usually these molds are found growing on wood mulch, but they also frequent any living or nonliving material close to the ground. They can be quite striking in appearance.
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. Bark mulches decompose with time, producing materials that the slime molds “consume.” Slime molds may be white, gray, yellow, violet, blue, green, purple–brown, or black 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. The image shows a slime mold on turfgrass. It shows small black structures on the blades.
Chemicals won’t work against slime molds. Remove large 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, 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,” which discusses slime molds in turf. The publication is available in Illinois Extension offices or at http://www.ag.uiuc.edu/~vista/abstracts/a401.HTML. An excellent site with images of slime molds is http://botit.botany.wisc.edu/toms_fungi/june99.html. A fact sheet on slime molds by Cornell University can be found at http://plantclinic.cornell.edu/FactSheets/slimemold/slimemold.htm. We usually see species of Physarum, Fuligo, and Stemonitis.