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3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915

3/10/03

Contacts:
Christine Baker, Plant Pathology, (515) 294-1741, cjbaker@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Yard and Garden Column for the Week Beginning March 14, 2003

Slime in the Yard and Garden

By Christine Baker
Graduate Student
Plant Pathology

Once in a while, gardeners find a yellow, slimy blob that looks like dog vomit in their garden and they become concerned for the health of their dogs or annoyed at their neighbors' unleashed dogs. However, this unsightly mass isn't dog vomit. It is really one of a diverse group of fascinating, fungal-like organisms called slime molds.

Several kinds of slime molds are frequently encountered on gardens and lawns in Iowa. Perhaps the most alarming is the one mentioned above, Fuligo septica, frequently called the "dog-vomit fungus."  F. septica is a bright yellow, orange or cream frothy blob up to 2 feet in diameter. It typically occurs after very wet, warm weather in the summer and favors damp, rotting wood mulch. Homeowners are often horrified to discover that the fungi is mobile, able to creep slowly across the ground, sometimes climbing onto plants or walls. As the organism matures, its body dries out, becoming tan-colored and crusty before disintegrating.

A variety of other slime molds are frequently found on turf, especially after warm, wet weather. Although they look very different from their mulch-loving cousin, they share a similar lifestyle. The most common slime mold on turf in this region is Physarum cinereum, which develops as 4- to 6-inch-diameter white, purple or gray oily patches covering the grass and thatch (the dead grass left after mowing.) As it dries out, Physarum produces spores in small, pinhead-shaped white or gray balls called sporangia, which make the grass blades look crusty. Often, these slime molds reappear in following years in the same spot of turf.

What is a slime mold?
Slime molds are not true fungi but primitive fungal-like organisms currently classified with protists. More than 700 different species of slime mold exist. Those found on lawns or flowerbeds have a two-part life cycle. During warm, moist weather the slime mold lives as a shapeless, growing blob called a plasmodium. The plasmodium may be gray, cream, colorless, bright yellow or orange. A plasmodium can slowly creep across the ground, moving like an amoeba and consuming bacteria, fungi and organic debris as it moves. Beds of shredded, decaying wood mulch are prime real estate for slime molds because mulch is especially full of tasty fungi and organic debris. Those that live on turf feast on the fungi and bacteria that live in the thatch. When the environment dries out, the plasmodium transforms its shapeless body into many small, often stalked, fruiting bodies that are full of dust-like spores. Sometimes, a plasmodium moves itself to a dry spot to accomplish this transformation. The dry, sporulating slime mold often looks hard and crusty. The tiny spores can remain dormant in the soil for years, waiting for another period of moist weather, when they germinate and each release a small, motile cell. Two motile cells fuse together and grow to become a new plasmodium, starting the cycle anew.

How can I get rid of it?
Slime molds are usually only a cosmetic problem, and they do not severely harm the plants they grow on or near. Slime molds on turf may cause the grass to temporarily turn yellow because they block the sun, but once the slime dries out and disappears the grass quickly recovers. In only extremely rare cases, a Fuligo plasmodium has been known to crawl onto a small garden plant and inadvertently suffocate it. Slime molds are usually considered beneficial organisms because they decompose dead organic matter and help the cycling of nutrients. They also may consume plant pathogenic fungi or bacteria in the soil, helping to reduce plant disease.

Although they are harmless and even helpful, it is understandable that most gardeners do not welcome homely slime molds. Because slime molds thrive in a moist environment, the best way to get rid of them is to allow them to dry out. Raking the mulch or grass to introduce air helps to accomplish this. Slime mold on turf also can be simply mowed off. Heavy thatch in the lawn provides a reservoir of organic matter and moisture, so reducing the thatch layer may help reduce slime mold growth. Chemical treatments rarely work.

The simplest thing to do is to learn to tolerate a little slime now and then. Untreated, a slime mold quickly disappears on its own as the weather dries out and it returns to its dormant, and invisible, spore stage.

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ml: isugarden

Editors: Two color photos, suitable for publication, are available at right. Click on each thumbnail photo to go to the fullsized photo. The top picture's fullsize photo is 500K and the bottom picture's fullsize photo is 396K.

Caption: Fuligo septica, the "dog vomit fungus" on wood. Photo courtesy of TomVolkFungi.net.

Caption: Physarum cinereum sporangia on turfgrass.

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