Artillery Fungus
Also Known as Shotgun Fungus

We have these small, black spots that look like specks of tar, all over our white, vinyl siding of our house. It's on the porch, my windows, but it is worse on the siding. It goes all the way up to my second-story windows, and is even under my soffit and on my gutters. What do you think it is?

The artillery fungus, or shotgun fungus, is a wood-decay fungus that likes to live on moist landscape mulch. The worst thing about this fungus is that it shoots spores up to 20 feet, which often land on siding, cars and anything else that surrounds the mulch. It seems to have become a serious problem the past few years for many homeowners here in Tennessee and though out the US. This year we’ve had a lot of customers ask for mulch recommendations. Although we are not in the landscaping business we have studied this problem and this is what we have found out.

Unfortunately no natural mulch can resist the artillery fungus – Penn State Plant Pathology department has tested 27 different kinds of mulch and found that with enough time all of the mulches were supporting the evil spore-shooting mushroom. The only way to ensure that artillery fungus never comes back is to take out the mulch completely and replace it with stone, artificial mulch or ground-cover plants. However, if you dislike stone and still want to replace the fungus infested mulch with organic mulch, the best way to keep the shotgun fungus away is to use a course ground of wood chips ( our playground chips would do ) or bark mulch.

The larger pieces of wood will stay mostly dry and the artillery fungus won’t like it as much as moist, finely ground mulch. Generally, the key to preventing the artillery spores from ever sprouting is refreshing your mulch regularly. As far as getting rid of the spores on your siding – that’s not a fun job. The most important part is to get them quick, as they are covered in sticky substance that will stay on the siding for good if not taken care of in a timely fashion. New vinyl siding that still has an oily residue on it can be power-washed within the first week. In other cases power-washing will be fruitless.

Scraping the spores off one-by-one with a scraper or steel wool is tedious but effective. After that there will still be a stain left, which can be taken care of with an ink eraser or possibly bleach. Bleach, Simple Green, toothpaste and alcohol-based mouthwash have been known to work with various rates of success, and can be tried first before attacking the spores with a scraper.

For removing spores off of cars oil, vinegar, car wax and tree sap remover have all worked for people that tested them.The bottom line is that no organic mulch is completely safe from the artillery fungus. If you know that shotgun fungus has been attacking your neighborhood switching to stone in the areas surrounding the house would be the safest choice. If you simply can’t stand stone, then refreshing the mulch every year would be the second best thing to do.

Yes, this is common on the sides of automobiles when cars are parked near mulched areas that are infested with the artillery fungus. It is especially noticeable on white sports cars – at least these are the owners that complain the most.
In fact, we have had complaints where private companies have artillery spores on 50-100 cars in their parking lots.

The next question asked is, “How do we remove the spots from the sides of cars?” We do not know, but some suggestions have included: power washing if the artillery fungus spots are very new and paint/wax on the cars is also new and shiny; automotive-paint rubbing compounds; and removal (if there are only a few spots) with the edge of a credit card. However, you must be very careful not to damage the car's finish. See some car owners' attempts at removing the spots from cars at the end of this section. These are NOT recommendations!!!

Not a problem.

The artillery fungus is a white-rotting, wood-decay fungus that likes to live on moist landscape mulch. It is in the genus Sphaerobolus (Greek for “sphere thrower”) and is very common across the USA, especially in the East, as well as many other parts of the world. The most common species in Pennsylvania seems to be S. iowensis (contrary to previous reports – including our own).

The artillery fungus is technically a “Basidiomycete” fungus (like the common mushroom that we eat), and probably is most closely related to a group of fungi called “earth stars". However, the artillery fungus is much smaller that the earth star that you may see occasionally growing in your yard. There may be other fungi and fungi-like organisms growing in your mulch.

The artillery fungus is quite small as you see on the left– the fruiting bodies are about 1/10 of an inch across and are very hard to see in the mulch. Artillery fungi are much smaller than the “bird’s nest fungus”with which it is often confused. By the way, the bird’s nest fungus does not actively shoot its spores – those little “eggs” of the bird’s nest fungus are splashed "splash cups."

This is extremely difficult to answer. The artillery fungus commonly occurs on dead trees, dead branches, rotting wood, etc. throughout the Northeast. I have seen it in the forest on standing dead trees and limbs on the ground, as well on wood in mulch-producing yards. If infested material is used for mulch, the artillery fungus may be already in the mulch when the load of mulch arrives at a job site, and may then grow rapidly along your foundation during cool moist conditions. However, this may be a problem only when mulch is not composted, which subjects the mulch to higher internal temperatures, which do not favor artillery fungi.

Or spore masses may already be present at a site on old mulch, previously infested plant leaves, rabbit or deer droppings, decaying leaves, and grass. These existing spores may immediately infest new applications of mulch. Remember nature "abhors a vaccum." In some cases, the spores also may be transported for very short distances via wind from adjacent infested sources. Spores may also be brought to the site on infested nursery plants, by being stuck to the undersurface of leaves, if the nursery also had an artillery fungus problem. When the leaves fall off onto the …here we go again! People can also spread the artillery fungus in various ways. Some homeowners make the mistake of sanding, scraping, or otherwise removing the spore masses from the sides of their houses, and letting them fall onto their foundation mulch. Such spores are dormant, but very much alive. Under proper conditions, they germinate and reinfest the mulch.

The term artillery refers to the fact that the artillery fungus actively (uses energy) shoots its spore masses, sort of like a cannon or howitzer (an artillery piece). We will call these “spores,” although they are technically spore masses, or gleba. The spores are usually shot only a short distance but the wind can carry them for longer distances and even up to the second story of a house. The term “shotgun fungus” usually refers to Pilobolus, a different kind of fungus commonly grows on fresh horse dung.

The term artillery refers to the fact that the artillery fungus actively (uses energy) shoots its spore masses, sort of like a cannon or howitzer (an artillery piece). We will call these “spores,” although they are technically spore masses, or gleba. The spores are usually shot only a short distance but the wind can carry them for longer distances and even up to the second story of a house. The term “shotgun fungus” usually refers to Pilobolus, a different kind of fungus commonly grows on fresh horse dung.

In nature, the artillery fungus shoots its spores towards sunlight. In the absence of direct sunlight, it shoots the spores at highly reflective surfaces, such as white house siding. And, of course, the black spots show up better on white surfaces, so they are noticed more easily.

This is a tough question. Wider recognition and awareness of the artillery fungus by the public certainly has led to a perceived increase in the problem. However, I think the problem is also realistically more severe than in past years, partly due to increased use of landscape mulch. There is more mulch being used these days, and therefore, more favorable material for the artillery fungus in our urban and suburban areas.

The artillery fungus may be just as common out in mulched flower beds far away from your house, but it is not noticed at that location. But, put the same mulch (and artillery fungus) next to your house foundation, add a white or reflective siding, and you may have a severe problem! In addition, it is my experience that the artillery fungus seems to prefer wood as opposed to bark. Much of the mulch that we use today is recycled wood – in the past, most mulch was bark. In addition, the finely-shredded mulches used today hold more moisture than the older coarsely ground mulches – this favors fungi, because they need moisture to survive!

The artillery fungus grows better and produces more spores during wet years, such as 2003 and 2004 (here in the Northeast). It is most common during the cool spring and fall, and is much less of a problem in the hot dry periods of mid-summer. And, not at all a problem during the winter here in Pennsylvania.

It is not your imagination, and you are a good observer. The artillery fungus often grows better in the mulch on the cool, shady, moist side of the house (usually the north side of the house here in the Northeast) where growing conditions are more suitable for the fungus.

Yes, they are alive, but not in the sense that they can hurt your siding. They are dormant, or sleeping, and pose no threat to the siding other than staining it.

The spore masses of the artillery fungus stick like super-glue. We have not found an efficient way to get them off without leaving a stain on the siding, especially on old dry siding. Power washing may work on brand new (only) vinyl siding that still has a shiny, oily, sheen. Each spore mass can be physically scraped, “steel-wooled”, or sanded off. Then the stain might be removed with an ink eraser, but this is a pain, literally.

Beware of any cleansers that have claims that sound “too good to be true”, with regards to removing the artillery fungus. It is likely that they are, in fact, too good to be true. At the end of this section I have listed some attempts that readers have used to remove artillery fungus.

Yes, this is possible, but only if the nursery had an artillery fungus problem on mulch in its pots or beds. But, this does not appear to be very common, at least in my experience.

No. All mulches that we studied eventually supported the artillery fungus after being outside for several years. However, some mulch performed better than others.

There has been 27 mulches tested in the field, and found that some supported more artillery fungus than others. In one study, the most resistant mulch was large pine bark nuggets. The large bark nuggets often stay hard and dry, conditions that the artillery fungus does not like. Cypress mulch also performed well, as it probably contains some anti-fungal, anti-decay chemical(s). However, there may be some environmental, non-sustainable reasons for not using cypress.

Used mushroom compost, also known as "mushroom soil," "spent mushroom substrate (SMS)," and even "black gold" is a great product, if you live in an area where you can get it! Mushroom compost has many beneficial aspects for gardeners, one which is that it supports micro-organisms that inhibit unwanted pest fungi.

Mushroom compost is pasteurized before it is used to grow mushrooms, and then the used compost is pasteurized again when it leaves the mushroom house, so it should not contain weed seeds. Our research at Penn State has shown that blending used mushroom compost with a landscape mulch at about 40% by volume (add 4 buckets of mushroom compost to 6 buckets of landscape mulch) will greatly suppress artillery fungus sporulation. Mushroom compost is very "green" and environmentally friendly.

They also have tested mulches of various colors, as well as the chemicals themselves that are used to color the mulches. The chemicals in our tests, at the concentrations used, did not inhibit the artillery fungus. Colored mulches appeared to very slightly, but only temporarily, inhibit the artillery fungus.

We attribute this to the colored mulches being slightly more water repellent and therefore remain drier than the non-colored mulches, at least at first. As the colors faded due to rain and sunlight, the artillery fungus moved right in. However an ideal situation for a mulch producer might involve mixing legally registered fungicides in with the coloring agent.

Interestingly, homeowners that put down a new layer of mulch each year generally have less artillery fungus problems. But, we have not confirmed this practice. But it does seem to work, if you don't miss a year!

You really need to ask this question to a compost expert, but most good mulch today is composted to some degree.

That will probably seal them in. It may solve your problem, but will give a pebbly appearance to your paint job. Each repainting will seal in the artillery fungus even more. You might consider using a good oil-based paint.

There are no fungicides legally registered (labeled) for use against the artillery fungus in landscape mulch. Bleach, if it worked, would be very temporary, since it leaches out with each rain. We have tested many different fungicides in the laboratory, but have to take the experiment to the field.

Some insurance companies will and others won’t. It depends on your insurance company, your agent, the exemptions in your policy, and especially your lawyer.

This is another difficult question, and one that lawyers like to argue. Mold is generally thought of as being a superficial, fuzzy fungus growing on damp or decaying organic matter. Like that fuzzy stuff on old “moldy” bread or on an old orange. The artillery fungus does exhibit such growth during part of its life cycle, when living in damp mulch, and therefore is (at least at times) a “mold” during part of its life cycle.

Biologically, the term "mold" has been used to generally describe a wide variety of different organisms such as slime molds, sooty mold, pink mold, blue mold in cheese, water molds, etc. These terms may be found in most modern, scientific textbooks or dictionaries dealing with “Mycology” (the study of fungi). This general biological usage makes the term mold very inclusive; under such a general usage, therefore, molds include many types of organisms, such as the artillery fungus, at least during part of its life cycle.

The spores on the side of your house are the reproductive structures of the fungus (although not biologically correct, think “seeds”). A good analogy is that they are shot like bullets from a gun. Just as the “bullets” are not the same as the “gun”, the “spore masses” on your house are not the same as a “mold”. Lawyers can put whatever spin they want on such terminology. And they do.


Since the artillery fungus can enter the chain of events at various places, I don’t see how anyone can be held responsible, unless they willingly supplied mulch with known artillery fungus in it. Which, of course, no good businessman would do! In my opinion, it is nearly impossible to prove where the artillery fungus entered the chain of events. This again is a subject for the lawyers.

Take out all of the infested mulch (usually just around the foundation - not out in the yard), bag it in a biodegradable bag, and take it to a landfill. Then put down a layer of landscape cloth or black plastic, and overlay it with stone or an artificial (non-organic) mulch.

Well, then, you may have to learn to live with the problem. That is, you cannot beat the artillery fungus (at this time), so try to manage it. Use mulches that the artillery fungus doesn’t like, such as large pine bark nuggets. Then, put down a fresh layer of mulch each year – we have no evidence for this, but yearly applications of layers of mulch appears to inhibit the artillery fungus.

Another possibility, but one we haven not investigated, is to use ground cover such as ivy, periwinkle, or pachysandra in place of the mulch around your foundation. It seems likely that the artillery fungus would not grow well under the canopy (on the fallen dead leaves) of such ground-cover plants. Or, establish lawn right up to your foundation. An artificial mulch made of plastic, old tires, etc. should work, since only artillery fungi only grow on organic material, but we have not tested it.

The best thing to do is probably bag it in a biodegradable bag and take it to a landfill. At least the mulch is organic and will rot away. Make sure you don’t put the infested mulch somewhere where you could be held responsible for someone else’s artillery fungus problem. This is out of my field, but it has been suggested that the infested mulch could be put in a yard waste-composting facility. But you really need to ask this question to a “compost expert.

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