What is Artillery Fungus?
What is Artillery fungus you ask? You just got your house washed and you now notice a bunch of black spots all over your siding. You try to scrape them off but they are stubborn. When you look closer, they are on the windows and up as high as the second floor!
This is artillery fungus. Below is a picture and some of the questions extracted from an article written by Dr. Donald D. Davis from Penn State University. He answers any and all questions as to how it arrives on your home.
Q: 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?
A: Sounds like you have the infamous “artillery fungus” Click here to see what the spores of the artillery fungus look like on house siding.
Q: I think I have 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 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.
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 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. Check out our publcation “What Is Growing In My Landscape Mulclh?”.
Q: I cannot see artillery fungus in the mulch – just how big is it? Is it the same as those little cups called the “bird’s nest fungus”?
A: The artillery fungus is quite small – 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.”
Q: Why is it called the “artillery” fungus? Is it also 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 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.
Q: Why do light-colored houses and cars have more problems than darker cars and houses?
A: 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.
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, 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!
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. And, not at all a problem during the winter here in Pennsylvania.
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 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.
Q: Are those spots alive? Will they hurt my house, like eat holes in my siding?
A: 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.
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 an efficient way to get them off without leaving a stain on the siding, especially on old dry siding. Add from Roof Refresh: We have tried and had success with the Mr. Clean Magic Eraser . They seem to work and not hurt the sheen on the siding or the shine on a car. This is our experience only. If you attempt it, try it in an inconspicuous spot.
Q: How did the artillery fungus get in my mulch? My neighbors do not 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. 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 vacuum.” 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.
Q: You mean that the artillery fungus can come in on plants and shrubbery that I have planted along my foundation?
A: 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.
Q: In your studies, have you found any wood/bark mulches that the artillery fungus absolutely will NOT grow on?
A: No. All mulches that we studied eventually supported the artillery fungus after being outside for several years. However, some mulch performed better than others.
Q: So what mulch(es) appear to be best?
A: We tested 27 mulches 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.
Q: I have heard that used “mushroom compost” will suppress the artillery fungus. Will it?
A: 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.
Q: How about artificially colored mulches?
A: We 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.
Q: Should I put down new mulch each year?
A: 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!
Q: How about composted mulch? Is it better or worse?
A: You really need to ask this question to a compost expert, but most good mulch today is composted to some degree.
Q: What if I just paint over the spores on my wood
A: 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.
Q: Are there any registered fungicides that will kill the fungus?
A: 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.