Introduction:

Slime molds in lawns feed on dead organic matter, protozoa, fungi and bacteria in the thatch. Under warm, wet summer conditions, they move onto turfgrass leaves where they develop into small round clusters of fruiting structures called sporangia. These sack-like structures are about the size of a pin head.

Purple spores contained within the grayish-white fruiting structures drop to the thatch and develop into amorphous masses of protoplasm. For more information on the development and life cycle of the slime molds refer to the web page on slime molds.

While slime molds are saprophytic on turf, they can cause the foliage to become chlorotic (yellow) if they persist for several days. Due to the reduction of light reaching the grass plus interference with respiration and transpiration, colonies of slime mold coating the blades can eventually result in the death of the grass.

These sack-like organisms can be found on clover and other weeds in the turf and on soil and thatch. Colonies of slime mold in turf can cover single blades of grass but are more commonly found in masses four to six inches across. Spots and streaks up to a few feet across have been observed.

Organisms involved:

Mucilago crustacea (Leyss.) Morg., Mucilago spongiosa (Leyss.) Morg., Physarum cinereum (Batsch) Pers. and Fuligo species are the common slime molds reported on turf. All commonly grown turfgrasses as well as the weeds associated with these lawns can be colonized by slime mold.

Control:

Vargas (1994) reports that chemical controls are a waste of time and money. Couch (1995), however, indicates that slime molds may be effectively controlled with any of the common turfgrass fungicides. Once the spore masses have formed on the grass blades, mowing, raking or watering is normally sufficient to remove the fruiting structures from the grass blades. Even in well-maintained lawns, infestations of slime mold may reappear in the same area year after year.

Baxendale, F.P. & Gaussoin, R.E. (Editors). 1997. Integrated Turfgrass Management for the Northern Great Plains. Extension University of Nebraska
Couch, H.B. 1995. Diseases of Turfgrasses - Third Edition. Krieger Publishing Company.
Vargas, J.M. Jr. 1994. Management of Turfgrass Diseases - Second Edition; Advances in Turfgrass Science. Lewis Publishers.
Watschke, T.L., Dernoeden, P.H., & Shetlar, D.J. 1995. Managing Turfgrass Pests; Advances in Turfgrass Science. Lewis Publishers.