Monday, November 12, 2012

Fungal frustrations

I've been wanting to write about this situation for quite a while, but only now have found the time: nuisance fungi in landscape beds. I'm going to zero-in on the two most aggravating groups: the stinkhorns and the artillery fungus. Other nuisances include the bird's nest fungi and certain true mushrooms. The "dog-vomit slime mold" is a very different sort of organism and was covered in our June 2011 blog post.

Stinkhorns. Wake Co., NC. Oct 2012. Photo: Greg Florian
Most stinkhorns are very conspicuous horn-shaped fungal fruiting bodies several inches tall that produce strong odors, unpleasant to humans. It's a bit hard to write about the stinkhorns without losing our PG rating, so I'll leave it to you, the reader, to look up the meanings of some of the Latin names if you want to know more. We received the image at left from a homeowner in Wake County. These are almost surely Phallus ravenelii, and they appeared in his mulched bed in early October. The submitter said he could smell them from two houses away. Is there a purpose to this odor, you ask? Take a close look at the picture and you can see that flies have been attracted to the stinkhorns. Why, you wonder? Well, the sticky green portion at the top contains the spores of the fungus. When flies visit, they pick up some of the spores and carry them away to new locations, so they're a means of dispersal for the fungus. You may have heard of a similar raison d'ĂȘtre for the foul smell of skunk cabbage, though in that case it's to attract pollinators. Fortunately for farmers and home gardeners alike, the odor does not persist once the fungi are gone.

Clathrus columnatus. Wake Co., NC. Jan 2008
Over several weeks in October and up until about our first frost, there were large numbers of stinkhorns in a the landscaped median of a major road near campus. Traffic didn't allow me to get a good look, but I think they were Mutinus elegans. This genus has a more tapered apex than Phallus. Back on January 18, 2008 I found a specimen of Clathrus columnatus on a south-facing slope here on the NCSU Campus. It had the smell of spoiled fish wrapped in a wet diaper. The fruiting body of this species has four "arms" fused at the apex.

Sphaerobolus gleba on siding. Jackson Co., NC.
Oct 2010. Photo: Christy Bredenkamp
Sphaerobolus gleba on gardenia leaf. Wake Co., NC. Oct 2012.
A very different dispersal mechanism is used by fungi in the genus Sphaerobolus. Their fruiting bodies on the mulch are small and inconspicuous, but they launch tiny dark spore balls for distances up to several feet, earning them the name "artillery fungus" or "cannonball fungus". The spore masses, known as gleba, stick fast to whatever they hit: plants, siding, and vehicles. Even when scraped off, they leave a stain, causing great frustration for the owners of affected homes and cars.

There's a lot more to these fungi than meets either the eye or nose. Their real "body" consists of a network of fine threads called hyphae that grow throughout the soil and mulch, where they decompose dead organic matter such as the mulch itself. The good news is that they do no harm to trees, shrubs, or bedding plants. The bad news is that there's no easy way to get rid of them. There are certainly no fungicides or disinfectants you can use in these situations. Removing stinkhorns as soon as they appear will help with the odor problem. Turning under the existing mulch and replacing it with composted mulch or a coarse pine bark mulch may help. Dr. Harry Hoitink of the Ohio State University has a very interesting fact sheet that includes a discussion of the microbial ecology of composts. One of his conclusions: "… water applied at the right time during composting, storage, and mulching can solve most of the fungal nuisance problems." Another very informative resource comes from Dr. Donald Davis at Penn State University. His Artillery Fungus FAQ gives details about this organism, how to deal with it, and suggestions from readers about how to remove the spots. It appears from reading his page that Dr. Davis has dealt with everyone from homeowners to attorneys about this issue.

Most fungi outdoors in North Carolina are going to be hidden from view over the winter, but keep the nuisance fungi in mind when planning your next landscaping project. You may be the next one to notice an unusual smell in the neighborhood.