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July 3, 1997

UNIVERSITY PARK, Pa. -- It barely takes up the space on a quarter of a match head, but the artillery fungus shot enough sticky, black spore masses at homes and automobiles last year to cause more than $1 million in homeowner damage claims in Pennsylvania alone.

Researchers in Penn State's College of Agricultural Sciences are involved in a five-year study of the fungus, commonly found in wood-based landscape mulch. Mulch beds can be infected by the fungus in various ways--it can grow on trees that become mulch, or a leaf that contains spore masses can blow into a mulch bed.

Artillery fungus, also known as shotgun fungus, is a wood-rotting variety that prefers sunny, damp areas. It is so small that even experts have trouble finding it in mulch, but it gives the wood a bleached appearance, says Larry Kuhns, professor of horticulture. This particular type of "mushroom" is a small cream or orange-brown cup containing a black, round mass of spores. Spore masses are produced when temperatures are between 50 and 68 degrees Fahrenheit, typical of the spring and fall seasons.

The fruiting body points itself toward strong light sources such as sun-reflecting glass and light colored buildings and cars. As the body matures, it opens like a flower, revealing the mass of spores in the middle.

Five hours after opening, the inner cup inverts and violently ejects the spore mass, with a 1/10,000 horsepower force, as far as 20 feet. The spore masses, which are sometimes mistaken for insect frass, adhere to any surfaces they contact. They cannot be removed without damaging or staining the surface and are viable for at least 10 years, says Kuhns, who is conducting the research with Don Davis, professor of plant pathology, and Beth Brantley, graduate student in plant pathology.

The project's goal is to examine the conditions under which Pennsylvania's native wood can successfully be used as fungus-free mulch, taking into account variables such as wood-to-bark ratios, the tree species (hard vs. soft wood) used in the mulch, how long it should be composted and whether mulch additives would prevent fungus growth.

"I don't have a lot of hope for fungicides because it's hard to determine when the mulch becomes infected, making the timing of the application critical and difficult," Kuhns says. "Preliminary results indicate that the fungus doesn't grow in rot-resistant woods like redwood, cedar and cypress," he adds, stressing that all results are very preliminary and experiments have not yet been repeated to validate the findings.

Brantley says the fungus seems to grow on either wood chips or "double shredded" bark mulch--the dark, organic-looking, thin-stranded mulch.

"We'll also be looking at ways to remove the fungus without causing staining or damage to adhered surfaces," Kuhns says, adding that except for cosmetic damage to man-made structures, the fungus is not a hazard in any way.

But this cosmetic damage is causing a lot of concern for the state's mulch-producing industries. Stringent new landfill regulations in recent years have forced increased recycling of waste products generated by wood-product manufacturers, lumber mills and land clearing for development. Consequently, landscape mulch production has become an important outlet for these wastes and a significant source of income for these industries.

As the demand for landscape mulch has increased for ornamental reasons, the fungus has become a larger problem. Mulch-producing industries fear widespread changeover to synthetic plastic or black pellet mulches.

Some businesses already have felt the effects of the fungus on their pocketbooks. Rick Shawley, president of the Bellefonte landscape company Nature's Cover, says he has had complaints on all seven mulch varieties he sells.

"To keep customers happy last year, I gave people 50 percent off of some products and paid a couple thousand dollars to appease everyone," Shawley says. "This year I'm selling quite a bit more decorative gravel."

The fungus is found nearly everywhere in the United States, except for dry areas like Arizona. It is a major problem in New Jersey, Ohio and Pennsylvania because of the type of wood available, Brantley says, and it is often confused with another fungus common to this region--the bird's nest fungus. There is little genetic information available on the artillery fungus, scientifically known as Sphaerobolus stellatus, but the bird's nest fungus probably is a close relative. The study, which is supported by the Pennsylvania Department of Agriculture, will include DNA analysis of the fungi, she says.


EDITORS: For more information, contact Larry Kuhns at (814) 863-2197 or Don Davis at (814) 865-1689, or point your Web browser at


Deepika Reddy
(814) 863-2703
(814) 865-1068 fax

How to clean Artillery fungus off your house.


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