Black spots/shotgun spores

What are those dark spots on my windows and siding?

Do you have little brown or black spots on your windows or siding?  Did they seem to show up out of nowhere?  Why are they only on some parts of the house and not others?

These spots are known as shotgun spores, or artillery fungus.  This is a fungus that grows in bark mulch.  If you look around your home, you will notice that the spores are only present near mulch beds.  They are called “shotgun” or “artillery” because the spores are shot out of the mulch and will stick to surfaces when they make contact.

We can remove them from your windows using razor blades or steel wool.  As far as the spores on your siding, that is harder to fix.  If you have newer vinyl siding, a powerwasher with heated water may remove the spores if they have not been attached for very long.  For older siding, or wood siding, or painted surfaces, there is not a good way to remove the spores without damaging the surface underneath.

There is no good solution for avoiding this problem.  There is no way to know if the mulch you are buying has the spores in it or not.  It can be in any wood-based mulch.