Artillery Fungus

What is artillery or shotgun fungus?

Artillery fungus is the common name for species in the genus Sphaerobolus, a group of fungi that breaks down dead wood. It is sometimes called shotgun fungus or cannon fungus because its mature fruiting body can eject a sticky spore packet with surprising force. The fungus is a natural recycler in the landscape; the nuisance begins when it grows in decaying mulch close to a home, vehicle, fence, or other surface.

The fungus forms tiny cup-shaped structures in damp, decomposing organic material. Inside each cup is a dark, sticky spore mass, often called a peridiole or glebal mass. At maturity, the cup turns toward a bright surface and launches that mass. University extension sources report that the packet can travel up to about 20 feet. When it hits siding or a leaf, its sticky coating helps it stay put.

Why are there black specks on my siding?

The spots are usually the launched spore packets themselves. They may look like pepper, tiny tar flecks, or small dark-brown bumps. They commonly show up on light-colored siding, trim, windows, cars, and plant leaves near wood mulch. The pattern and nearby landscape can offer clues, but artillery fungus can be confused with insect droppings, scale insects, tar, or other debris. If you are unsure, your county Extension office can help with identification.

Artillery fungus grows on decomposing wood and similar organic matter; it does not use vinyl siding as its food source. The dots are generally a surface nuisance rather than evidence that the siding itself is rotting. They can, however, be very difficult to remove and may leave marks or damage if someone uses an overly aggressive method.

When and where does it occur?

Look around the base of the wall for old, damp, heavily decomposed wood mulch, rotting leaves, or other decaying wood. The fungus can already be present in landscape material, and it may establish in a bed over time. The University of Tennessee notes that it grows on decomposing wood mulch and that spore masses can land on reflective surfaces and nearby plants.

Cool, wet weather can favor visible spore production, but the exact timing depends on local conditions. A fresh layer of mulch does not make the whole yard sterile, and no organic mulch should be treated as a guaranteed permanent barrier.

Can artillery fungus be washed off?

Sometimes a surface can be improved, but there is no dependable one-size-fits-all cleaning method. Once the sticky spore mass has dried and bonded to a surface, extension guidance warns that removal can be difficult and that scraping or other abrasive action can damage the material underneath. High pressure, harsh solvents, sanding, and metal scraping can also harm paint, vinyl, trim, or vehicle finishes.

If you want to try cleaning, identify the surface first, follow its manufacturer’s care instructions, and test a small, inconspicuous area. Stop if the finish dulls, scratches, or changes color. A professional can assess the material and discuss realistic options, but no cleaning company should promise that every spot will come off without a test.

How can I reduce the chance of more spots?

Prevention focuses on the source in the landscape. If old, decomposed mulch is directly beside the affected area, remove it and refresh the bed. Some extension recommendations suggest that a fresh layer can help act as a barrier; replacing the organic mulch with stone or another inorganic covering is a longer-lasting way to make that particular bed less suitable for the fungus. Large-nugget bark may be less supportive than finer wood mulch, but results vary and no organic choice is a guarantee.

• Inspect the bed beside the spots and remove heavily decomposed wood mulch and rotting debris.
• Keep mulch from touching siding and avoid piling it against the foundation.
• Consider stone or another inorganic mulch in the narrow area next to vulnerable siding, while maintaining proper drainage and plant care.
• Do not scrape the spots off the wall and let them fall into the mulch; the packets may remain viable and can add to the source material.
• Keep an eye on the wall after refreshing the bed. Existing spores in the landscape can remain, so prevention reduces risk rather than guaranteeing the problem will never return.

Homeowner questions

Is artillery fungus dangerous to the house?
The fungus feeds on decaying wood, not siding. The visible spots are typically a stubborn cosmetic problem, though aggressive removal can damage a finish.

Is it the same as mold growing on the siding?
No. The dark dots are deposited spore masses launched from a nearby growing site. Other stains can look similar, so confirm the cause before choosing a treatment.

Will replacing the mulch solve it?
It may reduce the source near the wall, especially if heavily decomposed mulch is removed, but spores can already be present elsewhere in the landscape. No change can guarantee that new spots will not appear.

Should I pressure wash the dots?
Use caution. The packets can adhere strongly, and high pressure may damage siding or paint before removing them. Identify the surface and test a low-risk option first.