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University of Illinois Extension

Slime Molds

Slime mold growing on mulch that is rotting.

Slime mold growing on mulch that is rotting.  


2 (1 = rare 5 = annual)


1 (1 = very little damage 5 = plants killed)


Slime molds may appear in maintained turfgrass as well as in organic mulched ornamental and vegetable 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.  

Life Cycle

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,  soil and on organic mulches. 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. In mulched flower and vegetable beds, drag a garden rake through the mulch to loosen/break apart the organic matter. After the onset of dry weather, you can hose down the turf area with water.  

Filed under plants: Flowers, Turf, Vegetables

Filed under problems: Fungal Disease

More information is available on Hort Answers.