Artillery Fungus on House Siding
By Gene Austin
March 3, 2001
If your siding, car, fence or any other surfaces around your house have broken out with a rash of black or dark-brown specks that do not want to come off, you are probably at war with something called artillery fungus.
It has become increasingly common in recent years, according to experts who have been seeking ways to control and eradicate it.
Artillery fungus, also called shotgun fungus or Sphaerobolus stellatus, usually originates in wood-chip mulch that is used around shrubs, flowers and other plants. Wet, rotting mulch breeds small mushrooms that shoot off spores for distances of up to 20 feet. The spores, which are sometimes mistaken for insect waste or bits of tar, cling tenaciously to surfaces such as house siding.
“It’s just like Super Glue,” said Don Davis, professor of plant pathology at Pennsylvania State University’s College of Agricultural Sciences. Davis and Larry Kuhns, professor of horticulture, have been leading a five-year study of the fungus, and they expect the study to continue for several more years.
Davis said he gets 20 to 30calls a week during the fungus’ most active seasons – generally spring and fall when temperatures range between 50 and 68 degrees. Davis said the rapid spread of the fungus and the growing number of fungus-damaged homes appear to be linked to the growing use of mulches made from recycled hardwood scraps and tree stumps.
Homeowners can take a key step to control artillery fungus by cleaning up wood-chip mulch around the house and disposing of it before the shooting starts again in April or May.
Here are some additional tips:
• Control. Bark mulch appears to be more resistant to the fungus than wood-chip mulch. Davis said pine-bark chunks seem to be the most resistant, and cedar, redwood and cypress mulch also appear to be resistant. “Even these mulches should be replaced every few years,” he said.
• Davis said stone mulch (usually small, decorative stones) “is the ultimate answer” to artillery fungus. Black plastic, held in place by stones or boards, is also safe, and some homeowners are getting good results with leaf mulch.
Kuhns said fungicides do not work well because “it’s hard to determine when the mulch becomes infested, making the timing of the application . . . difficult.”
• Insurance. If your house is damaged by artillery fungus, check with the agent handling your homeowners insurance. Most policies do not cover damage from fungus or mildew, but some do.
• Power-washing. Once the fungus becomes attached to a surface, even power-washing is not effective unless it is done within a few weeks of a fungal outbreak.
• One power-washing expert said he was able to remove the fungus using 200-degree water, with water pressure of 3,000 pounds per square inch, but this combination of hot water and high pressure can damage some types of siding.
• Scraping. Artillery fungus can be removed from windows by scraping with a razor blade. Scraping also can remove some of the black specks from smooth siding, but several homeowners who tried this reported that a brown residue remains and can’t be removed. Scraping can gouge vinyl and painted siding.
Gene Austin welcomes readers’ questions and comments, but he cannot give personal replies. Address correspondence to Gene Austin, the Philadelphia Inquirer, P.O. Box 8263, Philadelphia, PA 19101.