Artillery Fungus

artillery fungus
Closeup of the artillery fungus peridiole on automobile paint
Joey Williamson, HGIC, Clemson Extension

Joey Williamson, Ph.D.
Home & Garden Information Center

Have you seen small specks of what looks like tar on the siding of your home or on your car this spring? What you may be seeing are the spore packages, called peridioles, of a wood-rotting fungus living in the foundation mulch around your home. This fungus (Sphaerobolus stellatus) is known as artillery fungus and colonizes mulch that contains a high percentage of wood chips. During the cool, moist spring and fall temperatures, the artillery fungus produces very small, cup-like fruiting bodies on pieces of wood in the mulch. From these reproductive structures, the fungus is capable of shooting its sticky, black spore packages as far as 6 to 8 feet up and 20 feet out from the infested mulch. They will adhere tightly as if super-glued to the paint on a car, to the siding of a home and even to nearby plant foliage.

artillery fungus on leaves
Magnolia foliage covered with artillery fungus peridioles
Holly Thornton, Univ. of Georgia, Extension Plant Pathology

The appearance of these peridioles on foliage of nearby trees and shrubs may lead one to believe the plants have a leaf spot disease. Although unsightly, this fungus is not a plant pathogen. However, the eventual leaf drop by the affected plants does aid in the dissemination of the spores of the fungus to adjacent mulched beds.

There are no fungicides labeled for control of the artillery fungus in mulch, but there are cultural things that may reduce the incidence of this problem. If bark mulch will continue to be used, select mulch that contains at least 85% bark. The wood component of mulch contains cellulose that is the primary food source for these wood-rotting fungi. Bark contains lignin which is more slowly degraded by this or other wood-rotting fungi. Research indicates that the use of large nugget pine bark mulch may reduce the incidence of artillery fungus development. Additionally, adding a fresh layer of mulch on top of the existing mulch each year may reduce the sporulation of the artillery fungus. One must not apply so much mulch that the total layer exceeds 3 to 5 inches depth, as air movement into the soil is reduced. Covering existing mulch with a layer of pine needles may prevent sporulation of the artillery fungus. The addition of mushroom compost at 40% by volume with bark mulch will also suppress development of the artillery fungus.

Alternatively, one may remove the wood and bark mulch and replace it with synthetic mulch, such as shredded rubber mulch and artificial pine needles. These should last much longer and not provide a medium for growth of fungi. Groundcovers may be used in lieu of thick mulch in beds, and dense groundcover growth will help prevent the sporulation by the artillery fungus.

For more information on the various types of mulches available and mulch degrading fungi, see HGIC 1604, Mulch.

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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.