Artillery Fungus


(This 815th Buffalo Sunday News column was first published on November 12, 2006.)


As if that October storm wasn't enough, now we have a related problem for homeowners looming on the horizon.


Several weeks ago a reader wrote to ask what to do about small black spots on her vinyl siding. Unfortunately, her letter was lost when my computer went down during the storm. Even if I had access, however, I could not have been helpful as I had no idea what caused the spots.


Now things have changed, however. Last week Al Heiss wrote to provide a probable answer to the earlier inquiry and a warning for all of us who have white or pastel colored siding on our homes or similar colored cars.


I'll let Al tell his story: "After the 'October Surprise' storm, mountains of hardwood mulch are appearing all over Western New York. Some of that mulch will be given free or sold by towns throughout the area. While that sounds great to nearly everyone, the buyer should be aware, very aware, of one of the major problems associated with hardwood mulch.


"Last spring, I took between 8 and 10 yards of free hardwood mulch that Elma was giving its residents. Everything looked great until late August when little black dots started appearing on my siding.


File written by Adobe Photoshop® 5.0

Artillery Fungus Spores on a 6" by 8" Section of Siding

Photo by Al Heiss


Initially I thought they were spider droppings but the number steadily increased and I knew I didn't have that many spiders. While doing some research on the spots, I found they were spores shot at the light colored house by artillery fungus. The fungus is capable of shooting its spores 25-30 feet! Further research found that the artillery fungus is found mainly in hardwood mulch and has become a nuisance as more producers use hardwood scraps in their mulch."


Then Al adds the scary part: "I also found that nothing will dissolve the spots. There are some labor-intensive procedures including scraping the thousands of spots one at a time. The only catch is: a different spot is then left behind often untouchable by any cleansers."


Al suggested that I write to warn readers about this problem early next year. I do so now because some of you will already be planning to spread this mulch in flowerbeds near your homes.


Dr. Donald Davis of Penn State University maintains an informative website about the artillery fungus. The remainder of this column is based on information he provides there.


He tells us that the artillery fungus is a white-rotting, wood-decay fungus in the genus Sphaerobolus -- Greek for sphere thrower. It is in the same class of mushrooms as those we buy in stores, but it is tiny, its fruiting bodies only 1/10 inch across. Unfortunately it is also very common.


Normally, in summer or fall it shoots its spore masses or gleba only a few feet but the wind can take them much further. The spots they form on houses or cars are dormant living bodies but, other than the nasty stain they produce, they cause no damage.


Davis says that the gleba "stick like super glue" and adds, "We have not found a way to get them off without leaving a stain or damaging the siding." He warns against cleansers whose claims sound too good to be true: "it is likely that they are, in fact, too good to be true."


A team led by Davis studied 27 mulches for their production of artillery fungus. One conclusion they reached: "The mulches obtained from large piles of shredded blends of bark and wood supported significantly greater levels of artillery fungus sporulation than did other mulches. Such highly susceptible mulches should be avoided if the artillery fungus is to be minimized."


Although he does not recommend cleaning methods, Davis's website,, includes some that his correspondents have offered for both cars and houses. If you already have the problem, you should check these out. The suggestions include: corn oil, white vinegar, a mixture including detergent and bleach, and a number of commercial products, all also requiring much elbow grease.


Please understand that I do not argue against using wood mulch here. I do warn, however, against using it in beds close to light colored homes or cars.-- Gerry Rising