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Slime Mold

submitted by Sarah Browning, UNL Extension Educator

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Every year in late summer, an unusual type of insect makes an appearance in many landscapes. Actually, similar damage is caused by a small group of insects, called twig girdlers and twig pruners. Fortunately, these insects are not a serious problem, but their presence can be seen as small twigs at branch tips turn brown and die. In eastern Nebraska, oaks are the main host, but these insects can also potentially be found in persimmon, pecan, elm, hickory, honeylocust, hackberry, poplar, linden, redbud, basswood, dogwood and various fruit trees.

Wet conditions this spring have been perfect for the development of slime molds in landscapes and on the blades of turfgrass, making their identification a common question for UNL Extension offices right now.

Usually the call goes something like this, "There is something on the mulch in my flower beds. It looks like a dog vomited, but I know that can't be right because my yard is fenced and I don't have a dog. Can you help me figure out what it is?"

Or the question might be, "I have patches of dark gray fungus growing in my grass. How can I get rid of it before it kills my grass?"

Both of these questions point pretty clearly, for a horticulturist or plant pathologist, to slime mold.

What is a Slime Mold?

Slime molds are actually really interesting. At one time they were classified as primitive fungi, but are now classified botanically outside the fungi kingdom. They have been placed in the kingdom Amoebozoa, which means they are more similar to an amoeba than a true mushroom.

A slime mold begins its life by germinating from a spore, similar to a fungus, into a cell that can move. Cells swim through the water on the surface of leaf blades or pieces of mulch, and fuse together to form large masses. The slime mold exists as one cell, called a plasmodium, made up of many nuclei all held together in one large cytoplasm bag. Some plasmodia can grow quite large, like a large pizza, while others are small, about the size of a pinhead. Most often slime molds found in mulch are intermediate in size, about 4-5 inches across.

It grows by feeding on bacteria, fungal spores, and organic matter such as dead leaves and wood. It feeds by surrounding its food and secreting enzymes to digest it. Dead turfgrass leaf blades and thatch provide a good supply of organic matter for slime mold growth.

Slime molds get their name from one of their life stages, in which the plasmodium is a slimy, wet mass. One slime mold, Fuligo septica, resembles wet peanut butter in this stage. This is the feeding stage of the slime mold and is mobile, moving up to several feet a day. The plasmodium can be many colors- white, yellow, gray and shades of red.

When environmental conditions become hot or dry, this mass dries out and hardens. A recent caller described this stage of a slime mold in their landscape, as looking like dried expandable foam insulation. If wet conditions return, the wet slime mold stage returns and feeding continues. When the food source is exhausted, the mass again dries out and enters a stage of spore production. Spores may remain dormant in soil or leaf litter for many years until conditions are right for growth.

What Does This Mean for My Landscape?

Ok, so you have a slime mold growing in your mulch. What should you do? Break it up and wash it into the soil with water. Or scoop the mass out of the mulch and place it in the trash.

What if it's growing on your grass? Slime mold uses turf leaf blades as a surface for growth, but do not damage the grass at all. Rake the area to knock the growth off leaf blades, or use a strong stream of water to remove it. Fungicide applications are not necessary or recommended.

But be sure to take a moment to appreciate the slime mold for its uniqueness, before you get rid of it!

This resource was added June 2013 and appeared in the Lincoln Journal Star Newspaper Sunday edition. For information on reproducing this article or using any photographs or graphics, read the Terms of Use statement

University of Nebraska-Lincoln Extension in Lancaster County is your on-line yard and garden educational resource. The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office

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