Artillery Fungus Info

Common name: artillery fungus, cannon fungus, shotgun fungus

Scientific name: species of Sphaerobolus

What do artillery fungi look like?
They resemble a tiny cream or orange-brown cup with one black egg. The cup is approximately 1/10 of an inch in diameter. Areas of mulch with the artillery fungus may appear matted and lighter in color than the surrounding mulch.

Are they a problem?
They may be a problem. The fruiting body of the artillery fungus orients itself toward bright surfaces, such as light-colored houses or parked automobiles. The artillery fungus “shoots” its black, sticky spore mass, the “egg,” which can be windblown as high as the second story of a house. The spore mass sticks to the side of a building or automobile, resembling a small speck of tar. You may also find them on the undersides of leaves on plants growing in mulched areas.

Once in place, the spore mass is very difficult to remove without damaging the surface to which it is attached. If removed, it leaves a stain. A few of these spots are barely noticeable, but as they accumulate, they may become very unsightly on houses or cars.

What should be done?
To date, there are no known controls for this fungus. With support from the Pennsylvania Department of Agriculture and private mulch producers, Penn State reseachers are studying the problem. They hope to find a wood or bark mulch on which the artillery fungus will not sporulate.

One solution to the artillery fungus problem that is horticulturally sound is to replace wood-based mulch with other types of mulch, such as black plastic or stone, in critical areas adjacent to homes and parking areas.



Artillery Fungus – Frequently Asked Questions (FAQ)
Asked to
Dr. Donald D. Davis, Penn State
(Updated February 20, 2007)


These are typical, frequently asked questions (FAQ) that I normally field during the spring and summer (very seldom in the winter) — along with a brief summary of typical answers. Answers are meant to be (hopefully) informative, not very technical, and are not meant to offer concrete solutions. The questions are generally in the order that they are asked…

Q: We have these small, black spots that look like specks of tar, all over our white, vinyl siding on 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 soffitt and on my gutters. What do you think it is?
A: This sounds like you have the infamous “artillery fungus” which is also commonly called “shotgun fungus”.

Q: I think I’ve seen some spots on my car. Does the artillery fungus also get on cars?
A: 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 recently had several 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 don’t 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 attempts at removing the spots from cars at the end of this section. These are NOT recommendations!!!

Q: Does the artillery fungus hurt pets?
A: Not a problem.

Q: So, what exactly is the artillery fungus?
A: 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 artillery fungus is technically in the “Basidiomycete” class of fungi (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.

Q: Why is it called the “artillery” fungus? Is this also what is called the “shotgun fungus”?
A: 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 actually spore masses, or gleba. The spores are usually shot only a short distance, several feet, but the wind can carry them for longer distances and up to the second story of a house.

The term “shotgun fungus” usually refers to Pilobolus, a different kind of fungus that is common in dung, such as horse dung.

Q: Why do light-colored houses and cars have more of a problem than darker cars and houses?
A: In nature, the artillery fungus shoots its spores towards the light. 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.

Q: The artillery fungus problem seems to be much more severe now, than in the good old days. I don’t remember this being a problem 20 – 25 years ago. Why is it now a problem?
A: 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. Part of this is likely due to increased use of landscape mulch – there simply 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 beds far away from your house, but it is not noticed at that location. But, put the same mulch and the artillery fungus in the foundation mulch next to your house, add a white or reflective siding, and you may have a severe problem!

In addition, 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 probably hold more moisture than the older coarsely ground mulches – fungi need moisture to survive!!

Q: Why is this problem more severe in some years than in others?
A: 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.

Q: The number of spots seems to be worse on the north side of my house. Is this just my imagination?
A: It is not your imagination, and you are a good observer. The artillery fungus grows better in the mulch on the cool, shady side of the house (usually the north side of the house here in the Northeast) where growing conditions are more suitable for the fungus.

Q: Are those spots alive? Will they hurt my house, like eat holes in my siding?
A: Yes, they’re 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.

Q: So, how do I get the artillery fungus off my house siding? Will any cleaning chemicals remove it? Power washing? How about just plain scraping? Do the spores stick to all kinds of siding?
A: The spore masses of the artillery fungus stick like super-glue. We have not found a way to get them off without leaving a stain or damaging 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

Q: How did the artillery fungus get in my mulch? My neighbors don’t have it – only me! Why me!
A: 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.

Or spore masses may already be present at the job site on old mulch, previously infested plant leaves, or decaying organic matter such as rabbit or deer dropppings, decaying leaves and grass, compost piles, etc. These existing spores may immediately infest new applications of mulch. In some cases, the spores also may be transported for very short distances via wind from adjacent infested mulches or decaying organic matter. Spores may also be brought to the site on infested nursery plants, by clinging to the undersurface of leaves, if the nursery also had an artillery fungus problem. When the leaves fall off onto the mulch they inoculate the mulch… 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 and then inoculate the mulch.

Q: You mean that the artillery fungus can come in on plants and shrubbery that I am planting along my foundation?
A: Yes, this is possible, but only if the nursery had an artillery fungus problem in its pots or beds. But, this does not appear to be very common in my experience.

Q: Should I put down new mulch each year?
A: Interestingly, homeowners that put down new mulch each year seem to have less of the artillery fungus problem. But, we have not confirmed this practice. But it does seem to work. Don’t miss a year!

Q: What if I just paint over the spores on my wood siding?
A: That will probably seal them in; it may solve your problem, but will give you a pebbly appearance to your paint job. Each repainting will seal in the artillery fungus even more.

Q: Are there any registered fungicides that will kill the artillery fungus? How about a weak solution of household bleach?
A: There are no fungicides registered (by EPA) against the artillery fungus. Bleach, if it worked, would be very temporary, as it leaches out with each rain. We tested fourteen different fungicides in the laboratory, but have to take the experiment to the field.

Q: I can’t get those black spores off my siding, without leaving a lot of small brown stains. My siding is ruined. Will my homeowner’s insurance pay for residing my house?
A: 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.

Q: So, what is the final, ultimate solution to my problem???
A: Take out all of the infested mulch (usually just around the foundation – not out in the yard), bag it up, and take it to a landfill. Then put down a layer of black plastic, and overly it with stone, artificial mulch, or a good composted mulch.

Q: OK, I am going to remove my old, infested mulch. But, what do I do with it?
A: The best thing to do is probably to bag it up and take it to a landfill. At least it’s 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.