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Nasty Mulch-Borne Messes

Dog vomit mold and artillery fungus are likely candidates

Dog vomit mold, which thrives in hardwood-mulched beds, is gross but harmless. Not so with artillery fungus, which launches airborne spores that can ruin a home’s siding.

The abundance of rain this summer has created ideal conditions for the growth of artillery fungus and dog vomit mold. Gardeners who apply a fresh layer of mulch each spring are prime candidates for both problems. I have already seen one case of dog vomit mold, and I anticipate calls complaining that the color of their houses suddenly appears darker.
    Dog vomit is a slime mold that grows readily on organic matter such as hardwood bark mulch. Its name describes its appearance. It pops up in dark, shaded areas that can remain moist for several days. It will first appear as a bubbly dirty-white-to-pinkish blob five to eight inches long and two to three inches wide. Within a day or two, it will turn brown making it appear as if a dog dropped a load from the other end. Depending on how soon you discover it, it may have an odor.
    There are no chemicals you can use to rid the area of this slime mold and no chemicals you can use to prevent it. If you discover it in your landscape the only solution is to sweep it away with a rake and hope that it will not return. There is strong evidence that it is a more common problem where hardwood bark mulch is used and a lesser problem where pine bark mulch is applied. I have also seen it on colored mulches made from discarded pallets.
    Artillery fungus is the result of a saprophytic fungus releasing millions of black spores that are carried by a wind or a slight breeze. We have the proper conditions for artillery fungus to appear. Many years ago, extension agents on the Eastern Shore were overwhelmed with phone calls from people whose houses overnight changed in color from white to brown-black. In every instance, the homeowners had applied a fresh layer of mulch under and around their garden and foundation plantings. There appeared to be no differences among the types of mulches used.
    Those homeowners who took immediate action and power-washed the exterior of their homes were spared the expense of having to paint them. Those who allowed the fungus spores to dry on the siding had to scrape and sand before it could be painted.
    Both of these problems are unpredictable. But our recent weather — frequent heavy rains, high temperatures and high humidity — remind me of those years when both dog vomit mold and artillery fungus were problems. Beware.
    I have never experienced either of these on my property. I avoid them by not applying bark or wood mulches. I am a strong advocate for using compost as mulch. Bark contributes nothing of nutritional value to the soil, while compost provides nutrients. Plus the composting process kills disease-causing organisms and only beneficial organisms remain.


Heat Shock in the Garden

Q    Why are my green pole bean blossoms falling off? No beans in sight.

–Buddy Rapczynski, Lusby

A    It has been too hot. Cool the plants by misting them with water twice during the heat of the day.


Ask The Bay Gardener your questions at DR.FRGouin@gmail.com. Please include your name and address.