Artillery fungus

May 28th, 2000

These little tarry black dots on siding and fencing are the spores of mulch-borne artillery fungus.

   Lois Stewart was aghast when little, black tar-like spots started mysteriously appearing all over the new white vinyl deck railing and white aluminum siding at her Upper Allen Twp. home.

   “I thought it was some kind of bug coming off the hollies at first,” she says. “But this stuff just would not come off.”

   The mystery was quickly getting out of hand until Stewart went to a garden center and learned that the spots were not bug-related but were actually the work of a notorious wood-dwelling fungus known as the “artillery” or “shotgun” fungus.

   This organism – scientifically known as “Sphaerobolus stellatus” — helps decompose wood, plant debris and animal dung. It’s totally harmless to people, animals and living plants, but it has the nasty habit of shooting sticky, black spores up to 8 or 10 feet high and wide.

   That wouldn’t be a problem if we didn’t put siding, fences, railing and even cars in its way.

   But when these shooting spores hit such surfaces, they “stick like Super Glue,” says Dr. Larry Kuhns, a Pennsylvania State University horticulture professor who’s researching what to do about artillery fungus. “As it accumulates, it takes on the appearance that the house has been spray-painted with a clogged sprayer.”

   This little fungus has been causing big problems in recent years, not only in Pennsylvania but around the world. It’s become especially bad lately throughout the East Coast, where our cool, damp spring and fall weather is perfect for spore growth.

   The presence of the artillery fungus is difficult to detect because it is only one-tenth of an inch in diameter and orangish-brown in color. Usually the first time people notice they’ve got it is when those black dots – about the size of a round-headed pin – show up on the siding.

   Most often, the fungus is found growing in the wood mulch that’s become increasingly popular for weed prevention, moisture retention and neatness around homes. If enough of the fungus is present, the mulch can take on an orangish, bleached look.

   The problem is bad news not only for homeowners. It’s become an increasing headache for mulch producers, mulch suppliers and insurance companies, who are getting more and more claims from people who want reimbursed for having their houses and cars cleaned or repainted.

   Penn State researchers estimate the fungus is causing at least $1 million in damage per year throughout the state.

   “I run across it a lot, mostly on light surfaces,” says Anthony Baer, who owns A.R. Baer Painting in Mechanicsburg. “It’s hard to get off. It seems to eat its way into paint and even works into bare metal.”

    The artillery fungus shows up at people’s homes like the Stewarts’ in a variety of ways.

   It could show up in mulch that’s already infested or on plant material that has spores on the leaf undersides. It could come in on the droppings of animals that have eaten infested plants or wood. Or it could even show up on the fur and feathers of animals and birds that previously have visited infested areas.

   Given wood as a plentiful food source along with moisture and temperatures in the 68- to 77-degree range, the fungus reproduces readily.

   But it’s when the temperatures are a bit cooler – in the 50- to 68-degree range – that the real trouble occurs.

   That’s when the little cup-shaped fungus produces the black spores or “gleba” that are ejected over a two- to three-week period with amazing force up and out of the cup. Researchers say the thing even makes a sound as it ejects, although it’s not loud enough that you’d hear it walking by.

   What’s even worse is that the artillery fungus is “phototropic,” meaning it actually aims itself toward light or light objects.

   “That’s why you see it splattering house siding, cars, even white sheets that might be hanging on the clothes line,” says Kristen Akina, a graduate student who has been working on the fungal research with Kuhns and Dr. Donald Davis, a professor of plant pathology.

   Penn State researchers have been testing 22 different types of mulches and mulch blends in both lab dishes and in the field in bins next to white siding. They’ve also been looking at variables such as temperature, light and moisture and at ways to clean the spores off surfaces and prevent them from sticking in the first place.

   So far the research shows that the fungus colonizes much better in wood than in bark.

   Akina says wood contains mostly cellulose while bark contains mostly lignin. The fungus seems to prefer cellulose as a food source.

   Of the mulches tested, high-quality bark mulch with little or no hard wood in it was one of the best mulches for staying out of artillery-fungus trouble. Cocoa bean hulls, licorice mulch and cypress mulch also were effective fungus-fighters, says Akina.

   Artillery fungus grew best in mulches that were a blend of bark and hardwood, which unfortunately happens to be the type of mulch most often used by homeowners. Although the percentages of bark and wood may vary, this type of mulch typically is called “shredded hardwood mulch” or “tanbark.”

   When the Penn State researchers added treated sewage sludge and mushroom compost to the bark-wood blends, the fungus grew even faster. “That was like basically throwing a banquet for the organisms that already were in the material,” says Akina. “It added more food.”

   Curiously, though, when 100 percent compost was used as a mulch with no wood, spores did not grow.

   Akina says cedar mulch supported some fungal growth (although not as much as bark-wood mixes) but dyed or colored mulches did not inhibit growth.

   Because there is no organic food source in stone products such as crushed stone, pea gravel or marble chips, those are other fungus-resistant mulch options.

   “We found it doesn’t take a whole lot of light for the fungus to thrive,” says Akina. “Low light levels were not a problem, but it grew best in full sun. Temperature also makes a difference. This is a cool-season fungus, so it produces its spores in the spring and fall.”

   That’s exactly when Stewart’s problem began.

   Figuring she’d get a jump on the season this year, she had a new load of mulch put down at the end of March. When that string of cool, damp days hit in April, that’s when the black dots began appearing – some as high as 8 feet up on the siding.

   “SOS pads were the only thing that got it off, but I was afraid that would scratch the surface,” she says.

   Stewart’s husband, Jerry, had pretty good success getting the spots off the heat pump. He used a mobile-home cleaner called Protect All and let it soak in awhile before rubbing.

   Baer, the painter, says he’s been able to get the spots off unpainted aluminum or vinyl by using a cleaner called Night Spray 9.

   “You have to be careful if you put any cleaner on paint,” he warns. “If it’s petroleum-based, it will stain.”

   Or worse.

   That’s why it’s a good idea to test any cleaner on a small, out-of-the-way area before using it wholesale over a spotted wall.

   Penn State researchers say the spots are fairly easy to get off if you get to them early while they’re still damp. Once the spores harden, though, they’re tough.

   In Penn State’s test of artillery-fungus-cleaners, some of the best performers were Foaming Wheel Cleaner and Purple Muscle from Turtle Wax; Bleach Wite from Blue Coral, and a cleaning solution from Planet Solutions (sold through distributors or by contacting the company at toll-free 1-888-313-6183 or online at www.planetsolutions.org).

   “It takes some work to get the spots off no matter what you use,” says Baer.

   Penn State research also is taking a look at pre-treatments that homeowners can apply to surfaces ahead of time so the spores won’t stick very well.

   Kuhns says chemical controls to kill the fungus itself haven’t proved very effective, so it’s unlikely a spray for existing mulch will be the answer.

   However, simple raking can help somewhat by exposing the fungus to dry air and by dislodging the spores before they eject.

   Covering infested or potentially infested mulch with a layer of one of the fungus-resistant mulches also may solve the problem.

   But the Stewarts – now suspicious of wood mulch – decided to remove their new mulch down to the ground and go with stone or possibly all-bark mulch.