Aritillery fungus is Sphaerobolus, a common fungus that sticks to light or white colored surfaces and resembles spots of tar. The spots can be difficult or even impossible to remove without damaging the surface. This common fungus is often found in bark mulch, especially hardwood mulch. It is most prevalent on the north side of a building and shoots spores towards bright light. Once the fungus attaches it is very difficult to remove.
You may have seen artillery fungus and not even know it. The fungus resembles scaly dirt or mud spots and is found on light colored housing, cars and exterior surfaces. It is also found in manure and bark mulches. The name is derived from the Greek for “spear thrower” because of its ability to propel spores at quite some distance.
The best conditions for the formation of the spores are cool, moist and shady conditions. This is why the spores are more noticeable on the north side of a house.
Unfortunately there is no recommended artillery fungus treatment. If the spores are fresh, sometimes soap and water with a scrub brush will remove a bit of the fungus. You can power wash them, but such methods can be damaging.