Slime Molds

Mucilago, Physarum, and Fuligo spp.

Slime molds are different from most other turfgrass pathogens in that they do not directly infect the plant. Instead, this group of organisms feeds on microorganisms and decaying organic debris. During periods of warm, wet weather, slime molds migrate onto the surfaces of turfgrass leaves where they produce massive amounts of their reproductive structures, thus producing a white, blue, or gray patch.

Symptoms and signs

Grass blades and the surface of the soil may be covered with a translucent slimy, creamy-white growth. In a few days, this slimy growth changes to pinhead-sized masses of various colors (usually gray or blue). The affected areas may be from a few inches to many feet, with shapes ranging from rings to streaks or patches.

Disease cycle

Slime molds survive adverse conditions in the spore stage. In cool, humid weather, the spores absorb water. The spore wall cracks open, and a motile spore emerges. The motile spores feed on other microorganisms and decaying organic matter, but do not infect living turfgrasses. Eventually, pairs of spores unite and increase in size.This form of the organism is called a plasmodium, and it is this stage that produces the slimy overgrowth on turfgrasses. Slime mold plasmodia and reproductive structures may shade the grass leaves to the extent that leaves are yellowed, but damage seldom is severe.

Spore masses of slime mold fungus on Kentucky bluegrass lawn.

Spore masses of slime mold fungus on Kentucky bluegrass lawn.

Cultural control

Slime molds do not damage turf (apart from shading) and can be removed by sprinkling the leaves with water after the onset of dry weather. Removal of the dry spore masses by mowing, raking, brushing, or sweeping with a pole will aid in returning the grass to normal appearance. Chemical control is not necessary.