The following is information about artillery fungus. The UD plant diagnostic laboratory is receiving calls about the signs this pest leaves on structures and vehicles.
Artillery fungus is a nuisance pest in Delaware. We commonly receive calls about black spots on vinyl siding, glass doors, or cars near mulched planting beds caused by this fungus. The Artillery Fungus, Sphaerobolus, is a common decomposer of wood with very sticky spores that can be shot great distances. Wash off as soon as possible because once dry they can be very difficult to remove. Rake over mulch to break up fungal fruiting structures on the top surface of mulch to prevent more spore release. Raking will also help to dry out wet mulch, and the fungus needs high moisture to grow and sporulate. Sphaerobolus is more of a problem in mulch with a lot of wood (i.e. wood chips) because the fungus utilizes wood chips as a food source. Hardwood bark mulch with a high bark content doesn’t support artilllary fungus as well. The fungus is not pathogenic or hazardous to humans.
Artillery fungus spots on vinyl siding. Photo by Donald D. Davis, Penn State University
Information from Nancy Gregory, Plant Diagnostician, UD