The “artillery” fungus, or “shotgun” fungus (genus sphaerobolus), is a wood-decay fungus that lives and thrives on moist landscape mulch. When the cells accumulate enough liquid, the cupped cells invert causing the cells to burst and propel the spores as high as 20 feet where they adhere to surfaces such as house siding, cars, plants, or other structures; hence the nickname. The tiny black spores look like specks of tar on light-colored surfaces and are difficult to remove, often leaving stains.
Unfortunately, no natural mulch can resist the artillery fungus, especially after a really wet spring. And there’s no way to tell if your mulch is affected until it starts spotting your house. The only way to eliminate the artillery fungus is to remove the mulch completely. To get rid of old, infested mulch, place it in a biodegradable bag. Then, be sure to check with your municipality’s guidelines concerning yard waste disposal.
Homeowners can consider replacing it with stone, artificial mulch, or ground-cover plants. You can also play it safe by opting for a course, all-bark product, such as wood chips or pine bark nuggets, which are breathable. Refreshing your mulch every year would be the next best thing to do.
As for removing this nuisance fungus from the siding of your house… it’s not a fun job, and it can be very time-consuming. The most important part is to get them quick, as they are covered in a sticky substance that will stay on the siding for good if not taken care of in a timely fashion. As for removal, new vinyl siding that still has an oily residue on it can be power-washed within the first week of seeing the black spots.
In other cases, power-washing will prove unsuccessful. Scraping the spores off one-by-one with a scraper or steel wool pad is tedious but effective. After that there may still be a stain left behind, which can be taken care of with an ink eraser or possibly bleach. For removing spores off of cars, oil, vinegar, car wax, and/or tree sap remover have worked for people that tested them.
The bottom line is that no organic mulch is completely safe from this pesky “artillery” fungus. If you know that shotgun fungus has been attacking your neighborhood, switching to an alternative in the areas surrounding the house would be the safest choice.