Shotgun Fungus Can Shoot Black Spots Onto Your House

The culprit of the dark specks on your siding could be hiding in your mulch.

Mulching around your plants helps soil hold onto moisture, keeps the weeds down, and looks tidy. But with certain types of wood-based mulch, you might be providing a home to shotgun fungus, too. This fungus likes to live in damp, decaying wood, such as decomposing shredded bark mulch. You'd probably never notice it except as its name implies, shotgun fungus can forcefully shoot out spores. If your house is in the way of the spray, you'll see the results: Tiny black specks you can't rinse off with a hose. The good news is, the fungus isn't poisonous to you or your pets. But its extremely sticky spores are difficult to remove without damaging the walls of your house or any other surface the spores have landed on. The best thing you can do is to avoid it in the first place with these tips.

garden bed with mulch and plants
Doug Hetherington

What Is Shotgun Fungus?

It's hard to see shotgun fungus itself, because it's only two millimeters wide. Also known as artillery or cannonball fungus (Sphaerobolus), it uses internal water pressure to forcefully fire its spores (similar to seeds) up to 20 feet away. The fungus sets its sights on bright areas so that means it will aim for any pale surface that reflects light, such as the siding on your house. This mostly happens during cool, rainy spring and fall seasons, especially in shady areas, so you're most likely to find it on the darker, north side of your house. Artillery fungus stops making spores when the temperature is over 78°F, so you'll get a break in the summer.

How to Get Rid of Shotgun Fungus

The spores dotting your house may not fit in with your redecorating plans, but they won't cause any structural damage, nor will they grow there. They just won't come off very easily. If you have new vinyl siding that's still shiny, and you know that the spores haven't been adhering to the siding for more than a few days, you might be able to power-wash them away—but don't be tempted to sand or use harsh cleaner, because either one will likely damage your siding.

How to Prevent Shotgun Fungus

Though you may be stuck with a few black speckles for a while, here's how you can keep the fungus from shooting any more spores at your house:

  • Add a fresh layer of mulch. This will block any shotgun fungus in your decomposing mulch for about a year, which is about when you'd want to replenish your mulch again anyway.
  • Use big pieces of pine bark or other bark chips, which don't break down as fast as shredded bark mulch so shotgun fungus is less likely to take up residence.
  • Plant a low-maintenance groundcover in the area instead of using mulch.
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