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Slime Molds in the Landscape

May 29, 2002

Another landscape problem you can expect to see as a result of our recent moist weather is slime mold. Formerly considered fungi, these organisms are now considered to be groups of individual amoeboid cells. There are many variations of these organisms, and most prefer warm weather. As temperatures rise, slime molds will appear. Look for them on your 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 take nutrients from the plant material. They feed on decaying organic matter, fungi, and bacteria in the soil and the turfgrass thatch layer. 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 bases 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, brushing, or hosing down with a stream of water. Mowing the lawn usually removes the spore masses in turfgrasses. For more information, read Report on Plant Disease (RPD) no. 401, which discusses slime molds in turf. This publication is available in Illinois Extension offices or on the University of Illinois Vista Web site. Penn State has a brochure on materials growing in landscape mulch, with color photographs of slime molds. This brochure is available on the Web at http://pubs.cas.psu.edu/freepubs/u1201.html.

Author: Nancy Pataky


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