Artillery Fungus in Mulch

How did the artillery fungus get in my mulch? My neighbors do not have it - only me!

This is extremely difficult to answer. The artillery fungus commonly occurs on dead trees, dead branches, and rotting wood throughout the Northeast. I have seen it in the forest on standing dead trees and limbs on the ground, as well as on wood in mulch-producing yards. If infested material is used for mulch, the artillery fungus may already be in the mulch when the load of mulch arrives at a job site, and may then grow rapidly along your foundation during cool, moist conditions. However, this is likely a problem only when mulch is not composted, which exposes it to higher internal temperatures.

Or spore masses may already be present at a site on old mulch, previously infested plant leaves, rabbit or deer droppings, decaying leaves, and grass. These existing spores may immediately infest newly applied mulch. In some cases, the spores may also be transported very short distances by wind from adjacent infested sources. Spores may also be brought to the site on infested nursery plants, stuck to the undersides of leaves if the nursery also had an artillery fungus problem. When the leaves fall onto the mulch, the attached spores inoculate it.

People can also spread the artillery fungus in various ways. Some homeowners make the mistake of sanding, scraping, or otherwise removing the spore masses from the sides of their houses and letting them fall onto their foundation mulch. Such spores are dormant, but very much alive. They germinate and infest the mulch.

In your studies, have you found any wood/bark mulches that the artillery fungus absolutely will not grow on?

No. All mulches that we studied eventually supported the artillery fungus after being outside for several years. However, some mulch performed better than others.

So what mulch(es) appear to be best?

We tested 27 mulches in the field and found that some supported more artillery fungus than others. In one study, the most resistant mulch was large pine bark nuggets. The large bark nuggets stay hard and dry, conditions that the artillery fungus does not like. Cypress mulch also performed well, as it probably contains some anti-fungal, anti-decay chemical(s). However, there may be some environmental, non-sustainable reasons for not using cypress.

The article Artillery Fungus Sporulation on 27 Different Mulches- A Field Study from the Journal of Environmental Horticulture has some results.

How about artificially colored mulches?

We have tested mulches in various colors, as well as the chemicals used to color them. The chemicals in our tests, at the concentrations used, did not inhibit the artillery fungus.

Colored mulches appeared to inhibit the artillery fungus very slightly, but only temporarily. We attribute this to the colored mulches being slightly more water repellent and therefore remaining drier than the non-colored mulches, at least at first. As the colors faded due to rain and sunlight, the artillery fungus moved right.

Should I put down new mulch each year?

Interestingly, homeowners who put down a new layer of mulch each year generally have fewer arthropod fungus problems. But we have not confirmed this practice. But it does seem to work, if you don't miss a year!

How about composted mulch? Is it better or worse?

You really need to ask a compost expert about this, but most good mulch today is composted to some degree.

What if I just paint over the spores on my wood mulch?

That will probably seal them in. It may solve your problem, but it will give your paint job a pebbly appearance. Each repainting will seal in the artillery fungus even more.

You mean that the artillery fungus can come in on plants and shrubbery that I am planting along my foundation?

Yes, this is possible, but only if the nursery had an artillery fungus problem in its pots or beds. But, this does not appear to be very common in my experience.