The fungus Sphaerobolus stellatus, commonly known as Artillery Fungus or Shotgun Fungus, is a widespread organism that appears in landscaped areas using wood mulch. This fungus earns its name from its distinctive and forceful method of spore dispersal, which results in tiny, dark spots on nearby structures. Homeowners often encounter this nuisance when the spots appear on light-colored siding, cars, or windows, leading to concerns about property damage. This article addresses whether this common landscape organism poses any danger to human health.
Is Artillery Fungus a Health Threat?
Artillery Fungus is not known to be toxic, poisonous, or infectious to humans or household pets. Scientific studies classify Sphaerobolus stellatus as a harmless saprophyte, meaning it feeds only on decaying organic matter like wood, and it is not considered a pathogen of humans or animals. The tiny spore masses it launches, called peridioles, do not contain mycotoxins, which are dangerous substances produced by some other types of fungi. The primary risk associated with the fungus is cosmetic, relating to the tenacious adhesion of its spores to property. Concerns about inhalation are unfounded, as there is no evidence that the spores cause respiratory illness or allergic reactions in healthy individuals.
Identifying the Fungus and How It Spreads
The Artillery Fungus itself is a small, cup-shaped fruiting body, typically yellowish or orange, measuring only about two millimeters in diameter. This organism thrives in cool, moist, and shady environments, making wood-based landscape mulch its preferred habitat, especially in the spring and fall. For most of its life cycle, it exists as a network of thread-like filaments called hyphae, largely hidden within the decaying wood.
The signature feature of this fungus is its unique dispersal mechanism, which is strongly driven by light, a phenomenon known as phototropism. The fruiting body forcibly launches a single, dark, sticky spore mass, the peridiole, toward the brightest light source. This launch is achieved by a rapid inflation of a membrane beneath the peridiole, propelling the mass up to 20 feet horizontally or 14 feet vertically. The sticky coating ensures it adheres firmly to any surface it strikes, often a light-colored or reflective object like a car or house siding.
Dealing with Property Damage and Spore Removal
While the fungus is harmless to health, the resulting damage to property is a nuisance for homeowners. The launched peridioles dry into hard, black, tar-like spots that are difficult to remove, especially if they are left on a surface for more than a few weeks. The tenacious adhesive quality of the spores can even cause pitting on certain substrates, such as car paint or vinyl siding, during the removal process.
To remove fresh spots, the gentlest method involves physical scraping followed by scrubbing with hot water and soap. For more stubborn spots, anecdotal evidence suggests using products like hydrogen peroxide, white vinegar, or automotive bug and tar remover, such as Turtle Wax Bug & Tar Remover, which should be tested on an inconspicuous area first.
For surfaces like vinyl siding, a mixture of bleach water (one cup of bleach per gallon of water) can be applied, or a Magic Eraser can be used with caution to avoid removing the surface finish. On glass, a plastic razor blade can be used to carefully scrape the peridioles off, but on other materials, the process is labor-intensive and may not prevent residual staining.
Controlling Growth in Landscape Materials
Since there is no effective fungicide to eliminate Sphaerobolus stellatus, the best strategy is to modify the environment to discourage its growth. The fungus prefers wood mulch, particularly finely shredded hardwood products, which retain high levels of moisture and provide a rich carbon source. Replacing susceptible mulches with resistant materials is the most effective preventative action.
Alternative ground covers that limit the fungus’s ability to grow include inorganic options like gravel, stone, or marble chips. If organic mulch is still desired, switching to materials with a higher bark content, such as large pine bark nuggets or cedar mulch, can reduce the incidence of the fungus. Another method is to mix the existing mulch with composted material, such as mushroom compost, at a rate of about 40 percent to suppress the fungus. Regular raking of the mulch to increase air circulation and reduce moisture levels is also helpful.