Issue 9, June 19, 2009

Slime Mold Time

Wet conditions in late spring and early summer this year have brought out some interesting looking slime molds. Slime molds feed on decomposing organic matter, and can be found in almost any given spot in the home landscape; sidewalks, mulched areas, wood chips in play areas, or over vegetation such as turfgrass, strawberries, flowers, ground covers, weeds, and the base of woody plants. Mulched areas under shrubs and at the base of trees provide the perfect habitat for slime molds. These organisms were once believed to be fungi, but are now understood to be amoeba-like protists, similar to fungi.

They are not parasitic, so they will not cause direct harm to your plants or your family. Occasionally they can cause problems on lawns or low-growing ground covers by blocking the necessary sunlight that plants need to grow, but in most cases they are completely harmless. They feed on microorganisms in dead plant material.

Most slime molds are pretty. They range in color and size and may be white, gray, cream to light yellow, bright yellow to orange, violet, blue, green, or purple–brown greasy masses and can get as large as one to two feet in diameter. The plasmodium, or "feeding" stage, may appear as a slimy, amoeba-like organism. These organisms do "move", but too slowly to watch. There is a fascinating movie showing this movement on "You Tube". Homeowners are often concerned when, after a day to several days, they notice that the colorful and slimy "blobs" have migrated a short distance. Slime molds appear after a rain event in warm weather. Heavily irrigated landscape beds lined with mulch may provide the ideal setting for slime molds to grow.

Clients sending slime mold samples to the Plant Clinic are usually concerned with how to get rid of them. No chemical controls are known, nor needed, to combat slime molds. They usually dry up and disappear in dry weather. If you have a garden with some unsightly patches of slime molds that you wish to eliminate, simply remove the spore masses in a plastic bag and break up the remaining masses by vigorous raking or brushing.

One type of slime mold displays an unpopular resemblance to dog vomit. The plasmodium soon develops colorful, crusty fruiting bodies filled with masses of dusty spores. The image (courtesy of Jim Schuster) shows a slime mold on mulch in a garden bed.

For more information about slime molds, read Report on Plant Disease, no. 401, Slime Molds in Turfgrass. Another helpful site is a Cornell University fact sheet. An interesting site with images of mulch fungi, including slime molds, was created by Tom Volk, a University of Wisconsin mycologist.--Nancy Pataky

Nancy Pataky

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