Q: I have small black “bumps” (pin-head size) on vinyl siding on half of the front of my home (facing north). It appears like tar, but I have not been able to remove it with any type of solvent, including alcohol, nail polish remover, or gasoline. When I remove the little bumps with my fingernail, they are hard on the exterior but soft and gummy inside, like tree sap. Could this be some type of tree sap or mold or what?
A: The black spots are spores that come from fungus. The fungus usually originates in wood-chip mulch that is used around shrubs, flowers, and other plants. Wet, rotting mulch breeds small mushrooms that shoot off spores generally in spring and fall when temperatures range between 50 and 68 degrees. This fungus is more commonly referred to as shotgun fungus or artillery fungus because of the way it’s discharged, and it can shoot spores up to 20 feet.
To remove them from the siding, wet a towel with mouthwash, wipe down the spots until they soften, and then wipe off (6-7 swipes should do it). Then go over the stains with Mr. Clean Magic Eraser. The spots should disappear.
The best advice for preventing future outbreaks is to change your mulch every year. Freshening up your old mulch with new is only a temporary fix, you should completely remove all your old mulch and bring in new every year. The ultimate fix is to use mulch substance products or to use rocks for landscaping.