Artillery Fungus

Mulch provides an idea habitat for artillery fungus | Photo by Kathie Hodge

With the warmer temperatures and budding trees, there is no doubt that spring has fully sprung in the Richmond area. With the arrival of spring, it is likely that many people will be out and about in their gardens cleaning up from the winter, putting new plants in the ground, and mulching landscape beds to keep plants healthy and reduce the need for weeding. While most know the many benefits of mulch, one commonly overlooked issue, Artillery Fungus, can be introduced to your property when installing many types of mulch. This common fungus is not pathogenic to plants or animals and even though innocuous in appearance, it can be quite troublesome to homeowners in the way it spreads its spores on the landscape.

Artillery Fungus, Sphaerobulus stellatus, is an interesting organism that feeds off of decaying plant material and is actually quite beneficial as a decomposer in the landscape, breaking down mulch and slowly releasing nutrients into the soil. If that was all this fungus did, it would be of little interest and most would never even know that it exists.  It is the method of spore dissemination that makes this fungus extremely interesting and even problematic. The mature spores are ejected from the fungus using water pressure to fire a sticky spore mass towards the sunlight so that the fungus can spread as far as possible into new areas. You can see a slow-motion video of this action here: https://m.youtube.com/watch?v=T8OAmcUnm4g.

This is an amazing adaptation that allows the fungus to spread its spore over long distances but becomes a nuisance when the spores are fired towards light-colored objects on a property, such as your brand new white car or lightly colored siding. The light reflecting off of these items tricks the fungus into thinking that the area is an open sunny clearing, so spores are shot and stuck to the items rather than an intended target. While the spores are not dangerous, they are extremely sticky, and even scraping them off of the surface will likely still leave a small tar-like spot on the surface. After several years of growth on a landscape, houses and the like can easily end up looking like a splatter painting of small black dots all over the item. There are many tricks and tips online to remove the spores but know that it will be a chore and is not always successful.

While there is no good way to eliminate the fungus once it has established itself in the landscape, it is easy to prevent the introduction in the first place by choosing the correct mulch for your landscape. Any type of aged wood mulch is likely to introduce the fungus as mulch manufacturers and processors store groundwood in large piles to age and break down prior to application. These large piles are perfect breeding grounds for Artillery Fungus so nearly every batch of mulch will come with a fresh colony of the fungus. The use of non-aged mulch such as fresh wood chips, pine bark mulch, or pine tags will likely be free of the fungus because they have not been aged in bulk piles, preventing the development of the fungus prior to application.