I've received some emails asking me about little black spots that appear on the siding of homes. They seem to multiple until they are covering large sections of the side of the house. At first, homeowners think they are being attacked by birds or bats. They even think that some type of shell-less snail is gathering. It's none of those things. It's actually a self-firing little spore called Artillery fungus.
This is no joke. Artillery fungus is a wood-decay fungus that likes to live on moist landscape mulch. It is not dangerous to pets or humans, but it does make a mess of things. The artillery fungus can commonly be found on dead trees, dead branches and rotting wood. The artillery fungus may be already in the mulch if infested wood was used. Then, when the load of mulch arrives at a job site, the fungi grow rapidly along your foundation during cool moist conditions. The artillery fungi create dark brown spore packets that sit on top of specialized cup-shaped cells. As the cells accumulate sufficient liquid, the cupped cells turn over causing the cells to burst and throw the spore packets up to 20 feet high. They stick to surfaces like house siding, cars, plants, or other structures. Artillery fungus is a problem only when mulch is not composted. A batch of composted much is subjected to higher internal temperatures which would ultimately kill the fungus.
The spotting problem is most often seen on the north side of a house where the artillery fungus grows better in the mulch on the cool, shady side. The fungus, quite small being only about 1/10 of an inch across, is very hard to see in the mulch. The fungus shoots its spore masses only a short distance, but wind currents can carry them for longer distances. The fungus shoots its spores towards sunlight, but on the shady side of a house, it aims at highly reflective surfaces, such as white house siding.
Solution: Take out all of the infested mulch, bag it and take it to a landfill. Then put down a layer of black plastic and overlay it with stone or artificial (non-organic) mulch. Blending used mushroom compost with landscape mulch will greatly suppress artillery fungus spore populations. Mushroom compost is very "green" and environmentally friendly. Also, homeowners who put down a new layer of mulch each year generally have a less of a problem with artillery fungi.
The spore masses shot out by the artillery fungus stick like super-glue. Power washing may work on new vinyl siding, but old and dry siding presents a more persistent problem. There does not seem to be an efficient way to get them off without leaving a stain on the siding. They can be physically removed with steel wool or sanded off, but what a job that would be. Some people report that a combination of mouthwash and a stain eraser or toothpaste works.
Corn oil will work to loosen the spores from car finishes. It can be applied using a soft nylon pad. Wash it off immediately with soap and hose water after removing the spores. Another car expert advises that you wash the car first, then use bug and tar remover with a 100% cotton towel, as to not scratch the paint. This is supposed to work well with spores that have not been on the vehicle for a long time. Older spores need to be removed with a clay bar which you can purchase from most auto parts stores under the Mothers brand. You'll need to keep folding the material over, exposing new clay, to prevent built up dirt from scratching your paint. It's a great way to clean your car, but if not used properly, it becomes like sand paper.