Q. I have black spots all over my vinyl siding. Thousands of them, about the size of a ballpoint pen tip. They are hard, and when you pick them off, they leave a small brown stain. They are almost like tar. They are even as high up as my gutters, up to 15 ft. high. It seems they are only where my mulch beds are. I have heard that the mulch can spit its coloring out and also that it could be mold from the mulch. I have tried house and siding cleaner and a pressure washer to no avail. I also tried Krud-Kutter and a scotch brite sponge, which works, but would take five years to clean. Does anyone know what this is and what I could use to remove it?
A. This is artillery fungus. The stain is almost impossible to remove without removing the finish. The implications of having to remove the finish are depressing when dealing with vinyl siding, since the finish is part of the siding.
Information on the problem: Watch for slime molds to appear any time now. These growths suddenly show up after heavy rains or after watering plants in warm, muggy weather - even in the best of gardens! Slime molds are primitive organisms that flow (very slowly) over low-lying objects such as mulches, sidewalks, and driveways, or over vegetation such as turf grasses, strawberries, bedded flowers, ground covers, weeds, and the bases of woody plants.
Although these organisms cause much concern, they do not take nutrients from the plant material; they feed on decaying organic matter, fungi, and bacteria in the soil and the turf grass thatch layer. During warm, moist weather, the mold in its slimy, amoeba-like stage moves slowly over low-lying objects and appears as watery white, gray, cream-to-light-yellow, violet, blue, green, or purple-brown greasy masses as large as one or two feet in diameter. This stage soon develops into colorful crusty fruiting bodies filled with masses of dusty spores.
Chemicals do not provide control. Instead, for abundant molds, break up the unsightly spore masses by vigorous raking, brushing, or hosing down with a stream of water. Mowing the lawn usually removes the spore masses. Slime molds disappear with hot, dry weather, so we probably will have them with us for a while longer. For more information about slime molds, read Report on Plant Diseases No. 401, which discusses slime molds in turf.
The artillery fungus (also known as the shotgun fungus) is another fungus that thrives in wet weather and has become a nuisance with the popular use of mulch in planting beds near homes. The fungus, which grows in the mulch, is white and forms tiny (1/4 inch) puffball-like structures that contain spore masses. As these structures dry, the spore mass is "shot out" of the fungal vessel to a distance as much as 10 or 20 feet. These spore masses have a very sticky surface and stand out as black spots on sides of homes. You will find it nearly impossible to remove these spore masses from a home without removing the paint. A counterpart in the Ohio Extension system recommends using only bark-based mulch, especially true cypress bark, and avoiding wood-based mulches that were made from wood chips and ground-up wood pallets. In either case, it is recommended that the mulch be raked or stirred to help it dry out so that it is less desirable to the fungus.
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