UW Plant Disease Facts

Slime Molds

Authors: Ann Joy and Brian Hudelson, UW-Madison Plant Pathology
Last Revised: 05/22/2021
D-number: D0102
A dog vomit slime mold is shown spreading across mulch and up the base of a shrub.
A dog vomit slime mold is shown spreading across mulch and up the base of a shrub.

What are slime molds?  Slime molds are members of a shape-shifting group of organisms called myxomycetes.  These organisms are found all over the world, even in deserts, high altitudes, and on the edges of snowbanks.  Although they often resemble fungi, slime molds are more closely related to amoebas and certain seaweeds.

What do slime molds look like?  A slime mold spends most of its life as a lumpy mass of protoplasm, called a plasmodium, that moves and eats like an amoeba.  It may be white, yellow, orange, or red. The color of a particular species can vary slightly with temperature, pH, and the substances the plasmodium eats.  One very common slime mold, Fuligo septica, looks like dog vomit or scrambled eggs, from which it derives its common names.  Others resemble a network of veins or a fan.  In the course of a few hours a slime mold can transform from its amoeba-like phase into its fungus-like phase, which produces spores.

Where do slime molds come from?  The most common slime molds in Wisconsin love moist, shady places like crevices in rotting logs, leaf letter, and bark mulch.  Spores of slime molds are resistant to adverse conditions and will germinate after a heavy rain.  The plasmodium forms from many individual swimming cells called swarm cells.  The plasmodium can move at a very slow rate, feeding on bacteria, other microorganisms, and organic matter.  Changes in moisture or temperature, or exhaustion of its food supply can cause the slime mold to move to a drier, more exposed location to produce spores.

What do I do with slime molds in my garden or lawn?  Slime molds do not cause diseases.  However, they do use leaves and stems of plants as surfaces on which to grow and can block sunlight leading to leaf-yellowing.  The best way to get rid of slime molds is to break them up and dry them out.  Rake up and dispose of slime molds on bark mulch.  For slime molds on turf, mow the lawn, and rake up the thatch.  Alternatively, you may want to enjoy slime molds, if you find one in your yard.  These complex organisms are fascinating to observe with a hand lens and can be “captured” and grown indoors as a science project.

For more information on slime molds:  Visit Tom Volk’s website at botit.botany.wisc.edu/toms_fungi/june99.html, or contact your county Extension agent.

This Fact Sheet is also available in PDF format:

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Thanks to Dan Lindner Czederpiltz, Ann Wied, and Dennis Lukaszewski for reviewing this document, and to George Hudelson for providing the photograph.

A complete inventory of UW Plant Disease Facts is available at the University of Wisconsin-Madison Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.