Test Your Knowledge - June

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A Test Your Knowledge Unknown
Slime mold on blades of grass
Pamela Beckham 2010

Yes, this is a slime mold on grass. Despite their disturbing and oftentimes overnight appearance, slime molds do not infect grass and do not cause turf disease or injury, except by superficially blocking sunlight, which can result in temporary yellowing of grass blades.

Slime molds are primitive, fungus-like organisms that are classified as myxomycetes in the Kingdom Protoctista. Multiple species, including Mucilago crustacea, Didymium squamulosum, Physarum spp. and Fuligo spp. have been identified on lawn grasses. Depending on the species, they may be white, yellow, blue-gray, black, brown or pink.

A slime mold’s body is called a plasmodium, essentially a slimy, “blob-like” mass of protoplasm, much like a giant amoeba. Like amoebae, they feed by engulfing and then digesting their food, decaying organic matter and microorganisms. A plasmodium is the vegetative (feeding/growing) stage of the slime mold life cycle, and for the most part, is not noticed in the environment. Periodically, usually after heavy rain or irrigation during warm weather (April to September), the plasmodium moves up blades of grass, weeds and other means of support where it develops into structures known as sporangia (sac-like structures of asexually formed spores). Sporangia are the reproductive stage of a slime mold life cycle. Once dry, the sporangia have a powdery feel as a result of the spores. Wind, water, shoes and mowers help spread the spores. It is when the sporangia are forming that a slime mold is most visible. Irregularly shaped patches of sporangia can be several inches to more than a foot wide in the lawn.

Slime mold on a lawn'
Slime mold visible in a lawn
Pamela Beckham 2010

Since slime molds do not infect grass, it is not necessary to control them. They are essentially a cosmetic problem, and if ignored, will usually disappear within a few days to two weeks. Raking the grass, sweeping with a broom or hosing down the affected area with a strong spray of water will remove visible signs of their presence more quickly. Since slime molds tend to be more of a problem on lawns with heavy thatch, excessive irrigation and/or poor drainage, eliminating these conditions may reduce recurrence of the problem. For information on how to alter these conditions, see HGIC 2360, Controlling Thatch in Lawns, HGIC 1200, Aerating Lawns, and HGIC 1207, Watering Lawns.

To learn more about slime molds, including the “dog vomit” slime mold, see HGIC 2354, Spanish Moss, Lichens & Slime Molds and HGIC 1604, Mulch and the June 2008 Test Your Knowledge, “Dog Vomit” Slime Mold.

J. McLeod Scott
Home & Garden Information Center

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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.