Shotgun" or "Artillery" Fungus, Mold and Mildew

see also resource 1 and resource 2

Artillery or shotgun fungus has been a ever increasing problem in Ohio. In 1995 when we started our pressure washing business, we saw no cases of this on any homes, in 1996, three cases were observed, and as of 6/25/97, we have looked at over a dozen homes with the spores from this fungus on them. 

So what is Artillery fungus?

Occasionally we get a call about tiny, "mysterious black specks" appearing on a homes siding, a wooden deck, or other surfaces. The spots seem impossible to completely remove. Though the specks appear to resemble insect feces, scale crawlers or possible air-borne pollutants, they are actually mature spore masses expelled from fruiting bodies of a fungus known as "shot gun" or "artillery" fungus. This fungus develops in organic mulches. It is usually a greater problem in spring and fall, under cool, moist conditions under a temperature of 50 to 70 degrees. 

This very small type of mushroom Fungus is a cream or orange-brown cup containing a black round mass of spores which is very difficult to see. The mushroom fungus opens up like a flower, and seaks out bright light sources to shoot the spores at. Spores can be "shot" as high as the second floor of a building (about 20 feet), and can spot downspouts, soffits, windows, cars, sun reflecting glass and other bright surfaces. According to some scientists, the fungus can generate up to 1/10,000 of a horsepower when expelling these spores. 

These spores are one to two millimeters in diameter, black, sticky, and globular in appearance. The spores can also ruin the appearance of a wooden deck, though in these situations, it is easily cleaned and re coated. If you scrape the top of the black specks off with your finger nail you will reveal a reddish or cream color. 

We recommend using only non chlorine based cleaners, in conjunction with a coating which contains an EPA registered fungicide, such as Wolman F&P. 

It is theorized that artillery fungus can complete its life cycle only on wood (as in hardwood mulch), but not on bark, which has a lower carbon to nitrogen ratio. 

How can the Artillery Fungus be removed?

Attempting to remove the black tar-like spots from surfaces is generally futile, and extreme care should be used on aluminum siding and car paint since the finish may be damaged. In our experience, removing the fungus is possible through the use of a high flow rate of water (at least 5.5 g.p.m.) at 3000 psi, with hot water, at 200 degrees Fahrenheit, however, this process is only suitable if the fungus has not been in place for an extended period of time. The longer the fungus has been in place, the harder it is to remove from the siding. Generally, the time span for fairly easy removal, we feel, is approximately 2-3 weeks. Also this process will not work on most aluminum siding as the paint will not hold up to the extreme heat and pressure. 

Caution must also be taken on PCV coated siding, as the PCV surface does not withstand extreme temperatures well If the fungus has set in to the point that water removal is not possible, on vinyl, we have found that by washing with the same process, (thus removing the tops of the fungus, leaving only a tan or light brown spot) then rubbing with a fine grade of steel wool will remove the spots. This process is very time consuming though, and is only a last resort to removal of the fungus. This process should not be used on aluminum or PCV coated siding. 

What if we have this problem? Can it be prevented?

For locations plagued with this problem, consider switching to an inorganic mulch such as stone, pea gravel, etc. Or, a yearly addition of fresh mulch, so it completely covers old mulch, may lessen the problem, though it still may reoccur. We recommend complete removal of existing mulch prior to the application of an inorganic mulch, in order to lessen the chance of reoccurrence. It is also theorized that bark mulches may reduce the problem. 

If possible remove the mulch or place the mulch at least 30 feet away from any surrounding bright surfaces. Also Shotgun Fungus does not grow on cedar, redwood, or cypress which are on rot resistant woods. Avoid mulches made of wood chips or ground up wood pallets. Stirring up the mulch regularly to keep it dry retards the growth of Shotgun Fungus.

We also recommend treating the surrounding area with a fungicide, as well as cleaning up any animal droppings and rotting wood, as these are also prime conditions for the artillery fungus to grow in.

One other alternative is to apply a specialty coating to the surface, designed to inhibit the ability of the fungus and mold from growing on the siding. Though some spores may still appear, it will be much easier to remove as the spores will adhere to the coating, and not actually on the siding.