What Your Landscaper Never Told You!
I have these little black spots all over the front of my house, they go all the way up to the second floor WHAT ARE THEY?
I you live in New England I can guarantee that what you are asking about is the infamous “artillery fungus”.
The following questions and answers are from Dr. Donald D. Davis, Penn State.
Ok, so what the heck is “artillery fungus”?
The artillery fungus is a white-rotting, wood-decay fungus that likes to live on moist bark mulch you have around your home. 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 seems to be S. iowensis. 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.
I looked at my mulch, I don’t see anything.
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.
Why is it called the “artillery” fungus? Is it also called the “shotgun fungus”?
The term artillery refers to the fact that the artillery fungus actively shoots its spore masses, sort of like a cannon or howitzer. The spores are usually shot only a short distance, several feet, but the wind can carry them for longer distances, even up to the second story of a house.
Why do light-colored houses have more problems than darker houses?
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.
Why is this problem more severe in some years than in others?
The artillery fungus grows better and produces more spores during wet years, such as 2009 and 2010 (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 Massachusetts.
The number of spots seems to be worse on the north side of my house. Is this just my imagination?
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.
Are those spots alive? Will they hurt my house, like eat holes in my siding?
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.
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?
The spore masses of the artillery fungus stick like super-glue. We have not found a good, efficient way to get them off without leaving a stain or damaging the siding, especially on old dry siding. Power washing may work on vinyl siding that still has a shiny, oily, sheen, but in most cases power washing will only get about 50% of the spores off.
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 and you will damage your siding.
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.
How did the artillery fungus get in my mulch? My neighbors do not have it – only me! Why me!
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 is likely a problem only when mulch is not composted, which subjects the mulch to higher internal temperatures.
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. 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 mulch the attached spores 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. They germinate and infest the mulch.
You mean that the artillery fungus can come in on plants and shrubbery that I am planting along my foundation?
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.
In your studies, have you found any wood/bark mulches that the artillery fungus absolutely will NOT grow on?
No. All mulches that we studied eventually supported the artillery fungus after being outside for several years. However, some mulch performed better than others.
So what mulch(es) appear to be best?
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 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.
How about artificially colored mulches?
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
Should I put down new mulch each year?
Interestingly, homeowners that put down a new layer of mulch each year generally have a lesser artillery fungus problem. But, we have not confirmed this practice. But it does seem to work, if you don't miss a year! I have also heard that if you constantly turn your mulch over and keep it dry, you will also have lesser artillery fungus.
What if I just paint over the spores on my wood.
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.
Are there any registered fungicides that will kill the artillery fungus
There are no fungicides labeled for use against the artillery fungus in landscape mulch. We have tested many different fungicides in the laboratory, but have to take the experiment to the field.
I cannot 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?
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.
So, what is the final, ultimate solution to my problem???
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 black plastic, and overlay it with stone or an artificial (non-organic) mulch.
But, I don’t like stone - it’s so cold! I want to stay organic, and, like, use, like some sort of wood/bark mulch. Yet I can’t stand the artillery fungus. It’s driving me bonkers. What should I do?? I’m at my wit’s end.
Well, then, you have to learn to live with the problem. That is, you cannot beat the artillery fungus (at this time), so 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 really seem to inhibit the artillery fungus.
Another possibility, but one we have 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, but we have not tested it.