Nurserymen, landscapers, and greenhouse operators are occasionally contacted by homeowners seeking the identity of small black spots spattered on leaves of ornamental plants, siding, downspouts, soffits, and windows of their homes. Under certain conditions, nurserymen and greenhouse operators may themselves find the spots in their operation. Attempts to remove the spatters are generally futile, and identification of the source is then sought. The black spots often are misidentified as scale insects or insect excrement.
The spots do slightly resemble miniature soft scales or common fly speck. They are 1-2 mm in diameter and slightly raised to globular. The outer coating is actually brown and darkens with age. When scraped open, the center is found to be off-white, finely granular, and gummy.
These black spots actually have nothing to do with insects but are masses of mature spores expelled from fruiting bodies of the fungus Sphaerobolus stellatus Tode. A relative of the bird’s nest fungus, it is commonly called artillery fungus by mycologists.
Life History: The spherical fruiting body is approximately 2 mm in diameter and produces spores internally. When mature, it splits radially from the apex, forming 4-8 teeth along the outer rim of the now cup-like structure. The round mass of spores, known as the global mass or peridiole, is about 1 mm in diameter and rests in liquid at the bottom of the cup./ArtilleryFungusB.jpg)
The tissue layers in the fruiting body have separated by this time and remain attached only at the teeth. Approximately 5 hours after opening, the inner cup is violently everted, catapulting the glebal mass into the air. The everted inner cup can be seen as a pearl-like projection.
The Sphaerolobolus discharge mechanism, estimated to generate 1/10,000 hp (Buller 1933), can throw the glebal mass up to 6 m (Ingold 1971). Upon contact, the sticky coating adheres the mass to any surface it contacts. The fruiting body is strongly phototropic, and the glebal mass is generally shot towards the strongest source of light. Outdoors, this will be the sun or even highly reflective surfaces such as glass and light colored walls.
Hosts: Sphaerobolus stellatus grows on dung and well-rotted wood such as the tanbark and woodchips used as foundation bed mulches. It prefers open areas with little shade and sufficient moisture. In Pennsylvania, the fungus is most frequently found on the northwest exposure of homes, but it has also been reported growing on old benches in greenhouses and even indoors in mulched potted plants, where it spatters glebal masses on walls, draperies, and windows. With sufficient light, the optimum temperature range for the production of fruiting bodies is 10-200C. Because no fruiting bodies are produced above 25 0C (Alasoadura 1963), the problem is limited to spring and fall.Control: Fungicides have not been evaluated for control of this fungus. For those locations plagued with the problem, an alternate form of mulch for foundation beds may be in order. Yearly addition of fresh, treated tanbark or wood chips my lessen the problem if all the old mulch is completely covered. However, scraping glebal masses from windows and walls will possibly reinfest beds since the spores contained in the glebal mass have been reported to be viable for up to 11 years (Walker 1927). In greenhouses and other areas where S. stellatus is growing on rotted wooden structures, replacement of rotted wood, coupled with good sanitation, would eliminate the fungus.
Selected References
Alasoadura, S.O.. 1963. Fruiting in Sphaerobolus with special reference to light. Ann. Bot. 27: 123-145.
Boller, A. H. R. 1933. Researches on fungi. Vol. 5. Longmans, Green & Co., London. 416 pp.
Ingold, C. T. 1971. Fungal spores: their liberation and dispersal. Claredon Press, Oxford. 302 pp.
Walker, L. B. 1927. Development and mechanism of discharge in Sphaerobolus iowensis n. sp. and S.stellatus Tode. J. Elisha Mitchell Sci. Soc. -12: 151-178.
By Rayanne D. Lehman
Originally Published:
April 1985. REGULATORY HORTICULTURE Entomology Circular No. 93 (Vol. 11 No. 1)
Pennsylvania Department of Agriculture Bureau of Plant Industry
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