SLIME MOLDS Myxomycetes   F A C T S H E E T

Introduction

Slime molds are fungus-like organisms that have previously been classified as fungi, and later as Myxomycetes. They are no longer classified as fungi. Depending on the sources, there are now two or three different groups of slime molds, one of which is the myxomycetes. These now fall under the broader category of eukarya.

In general however, slime molds are characterized by the production of relatively large, single-celled, multinucleate bodies called plasmodia (singular = plasmodium). Plasmodia are the feeding stages of slime molds, and they are frequently seen on lawns, small plants, mulch, and decaying wood in late summer. Slime molds are not plant parasites, but they may injure plants by covering and shading them.

Symptoms

Slime molds are frequently observed when they form large colonies on mulch around trees or shrubs. They may initially appear as a slimy mound or mass, come in a variety of colors, and are often unsightly. Although slime molds are not plant parasites, they may injure plants by covering and shading them.

Figure 1: Yellow slime mold on mulch (provided by Dr. George W. Hudler, Cornell University). Figure 2: Slime mold on mulch (provided by Dr. George W. Hudler, Cornell University).

Life Cycle

Slime molds in the phylum Myxomycota are similar to fungi in that they reproduce by spores. When the spores are moistened, they germinate and give rise to microscopic amoeba-like organisms that either "flow" or swim in thin films of water. These organisms are larger than bacterial cells and will engulf and digest bacteria as they are encountered. Eventually several amoebae fuse, and when this happens, growth of the plasmodium begins. The plasmodium also preys upon bacteria and must have a moist substance on which to move. If conditions are favorable and food is plentiful, a circular plasmodium may become 2 feet or more in diameter. Most, however, are smaller than that and form a delicate net of brown, yellow, pink or white slime where they grow. The plasmodium moves "relatively rapidly", and may transverse a distance of several feet a day.

When substrates (logs, turf, mulch, etc.) dry and conditions for growth are no longer favorable, plasmodia aggregate to form spore-producing structures that resemble miniature puffballs. These "puffballs" may or may not be on stalks, their colors range from chocolate-brown to bluish grey to yellow to white, and their intricate beauty has attracted the interest of many naturalists.*

A new crop of spores forms within the structures, and the spores are blown away by the wind to eventually settle in new locations and start new colonies.

Management Strategies

Slime molds will disappear if left alone, but their unsightly appearance may cause some homeowners to desire a more rapid method of removal. There are no home garden pesticide products registered in New York State to manage slime molds on mulch. Individual colonies can be raked or turned under, or scoop up the colony and mulch it is under with a shovel, bag it, and place it in the garbage. Some slime molds can also be broken up or washed away with a forceful spray from a garden hose, but it' important to note that if conditions for the slime mold to develop are still present, and a food source is available, they may re-appear.

* Lee, Douglas, and Paul Zaul. 1981. Slime Molds. National Geographic 160 (1):131-136.

Created, KLS, 8/99; Updated, SLJ, 6/09