Fungus takes the fun out of mulch

Rainy days have brought unwanted guests into area gardens

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Gardeners are encouraged to mulch around their plants to conserve moisture, moderate soil temperature, reduce weed-seed germination, and beautify the landscape. With the recent heavy rainfall, however, many gardeners are finding unwanted guests in their mulch. Wood mulch, bark mulch, and other organic matter can be a source of interesting fungi and funguslike growths such as mushrooms, slime molds, stinkhorns, and artillery fungus. Organic mulches naturally decompose over time, and fungi and bacteria are the primary organisms involved in decomposition. Bacteria are microscopic organisms that are not visible. Fungi are also microscopic but may develop visible reproductive structures. The reproductive structure is often referred to as a mushroom. Usually the necessary process of decomposition goes on unnoticed by the gardener. However, occasionally these natural decomposers are noticed, particularly after rainy weather. Slime molds appear as bright-yellow or orange slimy masses that may be several inches to a foot across. (Other colors of slime mold include off-white, salmon, brown, and brick red.) This mold is a temporary nuisance and usually confined to a small area. Although slime mold isn’t a true fungus, it often is called “dog vomit fungus.” It feeds on bacteria growing in the mulch. Slime mold eventually dries out and turns brown, then becomes a white, powdery mass and eventually disappears. Stinkhorn, an upright 4- to 8-inch-tall fungus, has an offensive odor that emanates from the sticky spore mass on the tip of the fungus. This smell attracts flies, which land on the stinkhorn, then collect the spore mass on their legs and carry it to other areas. The structure resembles a giant slimy finger. View a photo of this fungus at Iowa State University Horticulture and Home pest news, www.ipm.iastate.edu/ipm/hortnews/2005/9-14/stinkhorns.html. Artillery fungus resembles a tiny cream or orange-brown cup holding a spore mass that resembles a tiny black egg. Areas bearing this fungus may appear matted and lighter in color than the surrounding mulch. Moist, rotting mulch provides an ideal growing situation for this fungus. North sides of structures, which tend to stay cool and moist, are more prone to artillery fungus growth. Artillery fungus — also called cannon fungus and shotgun fungus — may pose a problem for the homeowner. The artillery fungus “shoots” a black, sticky spore mass 6 feet or higher into the air, toward bright surfaces — including houses and parked cars. The spore mass, resembling a speck of tar, sticks to whatever it hits. The spore mass is hard to remove without damaging the surface, and it often leaves a stain. To help prevent artillery fungus-induced damage, avoid using wood chips or bark mulch next to structures you want to protect. Replace or cover mulch that has been in place for three years with a fresh layer. So what are the control options for fungi? There is no control for nuisance fungi. It is a good idea to purchase or use composted products that are low in wood content. Avoid fresh, finely ground wood products. Apply mulch to a depth of 2 to 4 inches, no more (and no volcanoes!). Stir the mulch with a rake to aerate the mulch, drying it out and making it less inviting to fungi. If you have small children or pets, rake out and destroy the fungi. Avoid eating any mushrooms, which may be poisonous. Mushrooms come in various colors, shapes and sizes. Some disappear soon after they emerge; others may be seen for a few days, and still others can last a whole growing season. You can find more information about slime molds and artillery fungus on the Web site of the Penn State Department of Plant Pathology, www.ppath.cas.psu.edu/EXTENSION/PLANT_DISEASE/mulchfun.html.
Jennifer Fishburn is a horticulture educator with the University of Illinois Extension Sangamon-Menard Unit. Contact her at fishburn@uiuc.edu.

About The Author

Jennifer Fishburn

Unit Educator, Horticulture University of Illinois Extension www.extension.uiuc.edu/sangamon

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