The use of wood mulch around homes has increased during the past ten years. The various mulches help to hold moisture in the soil, retard weed growth and have a pleasing esthetic value. Unfortunately, wood mulches also have a downside. They can harbor a fungus that can deface homes and automobiles.

The fungus has a common name of "artillery fungus" but is often mistakenly called shotgun fungus. It is actually a miniature mushroom that dwells in most decaying wood mulches. This particular type of mushroom is the size of a fourth of a match head. The mushroom cup is cream or orange-brown colored and contains a black, round mass of spores. Spore masses are produced when temperatures are between 50 and 68 degrees, typical of our spring and fall seasons in Butler County.

The tiny mushroom points itself toward strong light sources such as light colored building or cars or sun-reflecting glass. As it matures, it opens like a flower, revealing the mass of spores.

Five hours after opening, it violently ejects the spore mass up to a distance of 20 feet. The spores attach themselves to whatever surface (house or car, for example) is in the way. The end result is small black spots that resemble tar. Removal of the spots is very difficult and a permanent brown stain remains.

Artillery fungus can cause considerable cosmetic damage to homes and automobiles, but it is not a hazard in any way.

Penn State researchers have been evaluating different mulches to determine which will not support the fungus and are suitable for use by homeowners. They also have been investigating procedures for removing the tar-like spots.

Testing began in 1998. Twenty-seven different mulches were field-tested. Included were several barks, a number of woods, both dyed and natural, compost and 100 percent spent mushroom manure. After four years, the best mulches were found to be 100 percent spent mushroom manure, pine bark nuggets and shredded cypress.

Based on the results of the 1998 test, a new series of tests were initiated with blends of spent mushroom manure and hardwood mulch. The results of this investigation are currently being evaluated. A 50-50 blend of spent mushroom manure and hardwood mulch suppresses the artillery fungus.

The use of spent mushroom manure for mulch is significant because huge quantities of it are produced in Pennsylvania. It is generally viewed as an undesirable byproduct within the mushroom industry. Its use for mulch would solve a disposal problem for them.

Penn State is currently evaluating the latest test results. Until the results are available, they suggest that since all wood/bark mulches will eventually support the artillery fungus over extended time periods (three or four years), all mulches should be replaced, or covered with a fresh layer on a regular basis.

Since we live in an area with a large mushroom mine, spent mushroom manure is readily available. If you are adventurous, you may want to conduct your own test with it.