What Are the Black Dots on My Siding? Artillery Fungus, Explained

What artillery fungus is

Artillery fungus (Sphaerobolus stellatus) is a wood-decay fungus that colonizes hardwood mulch — the shredded brown mulch used in almost every Kansas City flower bed. When it fruits in cool, damp weather, it builds tiny spore cannons that aim at bright surfaces and fire sticky black spore masses with surprising force. Light-colored siding, white garage doors, gutters, and parked cars are its favorite targets, which is why the dots always seem to cluster on the wall facing a mulch bed.

How to identify it

• Dots the size of a ballpoint pen tip (1–2 mm), dark brown to black, slightly raised
• Concentrated on walls, doors, or cars within about 20 feet of hardwood mulch beds
• Usually from ground level up to 8–12 feet — roughly second-story height at the extreme
• Stuck hard: a fingernail can pop one off, but it leaves a brown stain beneath
• Worst after cool, wet stretches — Kansas City springs and falls are prime season

If the specks wipe off easily, you are probably looking at fly droppings or aphid residue instead. Artillery fungus fights back.

Why it is so hard to remove

Each spore mass is coated in a natural adhesive that cures like glue in the sun. Power washing alone will not remove cured spots — turning the pressure high enough to blast them off will damage vinyl and paint first. Household cleaners do not dissolve the adhesive either, and aggressive scrubbing grinds the pigment into the surface. This is one of the very few exterior stains where the honest answer from any professional includes the word “partially.”

What professional removal looks like — and honest expectations

Our approach at KC Splash is a soft wash pre-treatment to soften the adhesive, followed by careful manual work on the spots, then a full house wash so the wall reads clean and even. Here is the truth most companies will not put in writing: fresh spots (under about 3 weeks) usually release cleanly; spots that have baked on for months can be improved but may leave shadow stains, especially on light vinyl. Anyone promising 100% removal of old artillery fungus sight-unseen is telling you what you want to hear.

How to keep it from coming back

• Swap the mulch within firing range. Replace hardwood mulch within 20 feet of the house with pine bark nuggets, pine straw, rubber mulch, or stone — artillery fungus rarely colonizes them.
• Refresh yearly. If you keep hardwood mulch, top-dress with 2–3 fresh inches each spring; the fungus lives in old, decaying mulch.
• Watch the wet shade. North-facing beds that stay damp are the launch sites; improve drainage and airflow where you can.
• Act fast on new dots. The removal clock starts the day they land — call within days, not months.