What Is Artillery Fungus, and How Can It Be Prevented on Homes?

If you’ve spotted small, dark specks scattered across your home’s siding and they won’t wipe away, what you’re looking at is likely artillery fungus. This is a wood-decaying organism with a remarkable ability to launch spores up to 20 feet from mulch beds onto nearby surfaces. While artillery fungus poses no health risk to humans, pets or plants, its spores bond tenaciously to siding and can remain viable for over a decade.

Learn what artillery fungus is, why it targets light-colored surfaces, what prevention methods work and how to get rid of it early before spores fully set.

What Is Artillery Fungus?

Artillery fungus is a wood-decaying organism that thrives in moist, rotting organic material. Its scientific name is Sphaerobolus stellatus, and it’s commonly called shotgun fungus or cannonball fungus. These names come from the way the organism spreads, launching its spores in a pattern that resembles a spray of projectiles.

This fungus develops primarily in non-composted wood mulch and other decomposing organic materials near your home’s foundation. 

Is Artillery Fungus Harmful to Humans?

This fungus is not harmful to humans, pets or plants. It also causes no structural damage to your home. The primary concern is cosmetic, as the spores create visible spots on exterior surfaces.

What Causes Artillery Fungus?

Understanding what causes artillery fungus on your house starts with recognizing the breeding ground. Non-composted wood mulch near your foundation provides the ideal environment for this organism to develop. The fungus feeds on the decomposing wood material in moist, sheltered mulch beds.

Once established, the fungus produces a remarkable spore-ejection mechanism. Powered by osmotic pressure, the fungus can launch artillery fungus spores up to 20 feet from their source. The ejection is even accompanied by an audible sound. A 2024 peer-reviewed study confirmed that the fungus uses a snap-through buckling mechanism and wastes very few spores.

The fungus displays phototropic behavior, meaning spores aim toward the strongest light source. For that reason, light-colored siding and glass are the most common targets. Homeowners have even reported more spots on lighter-colored cars parked beside darker ones, illustrating this light-seeking pattern in action.

Artillery fungus is most active during spring and fall when temperatures range between 50° and 70° Fahrenheit. Above 77° to 78°, the fungus stops producing fruiting bodies. Perhaps most concerning is that spores can remain viable for up to 11 years, which makes early intervention critical. Based on its seasonal growth patterns, spring is the ideal time to schedule a house wash treatment to address any emerging spots.

How to Identify Artillery Fungus

Before taking action, confirm what you’re dealing with. Artillery fungus spots measure 1 to 2 millimeters in diameter and appear slightly raised with a globular shape. The outer coating is brown and darkens with age. If you scrape one open, you’ll find an off-white, finely granular, gummy center.

These spots are often mistaken for tar spots, scale insects, or insect excrement. However, several distinguishing factors set artillery fungus apart. Mold appears fuzzy and irregular and grows in dark, damp areas without direct sunlight, while algae presents as slimy green growth in shaded spots with a very different texture and location pattern. Insect droppings typically cluster tightly together, whereas fungus on siding displays a scattered, widespread distribution.

One reliable location clue can help with identification. Artillery fungus almost always appears in relation to a nearby mulch bed, rotting wood, or foundation plantings. If you see the characteristic dark spots and you have mulch near your home, you’re likely dealing with this particular organism.

How to Prevent Artillery Fungus on Your Home

Prevention is far more manageable than attempting to address bonded spores after the fact. Taking proactive steps now protects your home’s exterior and saves considerable effort later.

Environmental Management

Start with the mulch bed itself. Rake and turn your mulch on a regular basis to disrupt fungal growth and improve air circulation. When artillery fungus is found in mulch, remove it entirely rather than layering fresh mulch over it. Spores can re-emerge through new material.    

Never scrape spots off your siding and let them fall back onto the mulch bed. Spores remain dormant but alive, and this practice leads to re-infection. With spores viable for up to 11 years, proper disposal is essential. Remove affected mulch from your property entirely. Do not compost it on-site, which will only perpetuate the problem.

Regular Maintenance

Consistency provides the best long-term defense against artillery fungus on your house. Penn State research found that homeowners who add a fresh layer of mulch annually tend to experience fewer artillery fungus problems. This practice helps prevent the deep decomposition that creates ideal fungal conditions.

Conduct routine exterior inspections during spring and fall, the peak active seasons for this organism. If spots appear, act within the first two to three weeks before spores fully bond to surfaces. This narrow window offers your best chance at addressing the issue. An annual house wash fits naturally into a whole-home exterior care routine and helps maintain your siding’s condition year-round.

Material Choices

Selecting the right mulch makes a significant difference. The Penn State research tested 27 different mulch types in field conditions to determine which materials resist artillery fungus most effectively. Large pine bark nuggets performed best because they stay hard and dry, creating unfavorable conditions for the fungus. Cypress mulch ranked second, likely because it contains natural anti-fungal compounds.

Colored mulches provided only slight, temporary resistance before the fungus took hold. Color alone is not a reliable deterrent. For the strongest protection, consider fully inorganic options. Rubber mulch, stone or gravel will not support any artillery fungus growth, eliminating the problem at its source.

How Do You Get Rid of Artillery Fungus?

The reality is that once spores fully bond to siding, they are extremely difficult to address without risking surface damage. No fungicides are registered or proven effective for use against artillery fungus. The critical window is early, within the first two to three weeks after spots first appear, before full bonding occurs.

Standard power washing does not remove it either. Artillery fungus removal requires mechanically scraping the spores from surfaces through gentle cleaning and completely removing contaminated wood mulch from your landscaping to eliminate the source. Stronger cleaning methods, like using bleach, may be necessary for stubborn spots. Applying improper pressure can damage your siding surface and potentially void your home’s warranty.

The composition and tenacity of bonded spores make them nearly impossible to remove once they’ve fully set, which is why prevention and early action are so important. While artillery fungus that has fully bonded is notoriously resistant and cannot be removed through power washing, early professional house wash treatment gives your home’s exterior its best chance. An annual treatment plan is the most effective way to maintain your siding’s condition and address spots before they set.

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