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Phytotoxicity to Crop Plants and Herbicidal Effects on Weeds of Viridiol Produced by Gliocladium virens. C. R. Howell, Research plant pathologist, Agricultural Research Service, U.S. Department of Agriculture, National Cotton Pathology Research Laboratory, P.O. Drawer JF, College Station, TX 77841; R. D. Stipanovic, research chemist, Agricultural Research Service, U.S. Department of Agriculture, National Cotton Pathology Research Laboratory, P.O. Drawer JF, College Station, TX 77841. Phytopathology 74:1346-1349. Accepted for publication 14 June 1984. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-1346.

When the biological control agent, Gliocladium virens, was grown on an autoclaved rice medium, it produced a phytotoxin that caused necrosis of cotton seedling radicles. The phytotoxin was identified as viridiol, a compound previously reported from G. virens. Viridiol, a close relative of the antifungal compound viridin, had little antibiotic activity against a variety of fungi and bacteria, but it was herbicidal to germinating pigweed seed when used in vitro. Because of its instability, viridiol was not an effective herbicide when it was introduced into field soil. However, when a dried and ground preparation of G. virens cultured on rice was worked into pigweed-infested soil above planted cotton seed, viridiol apparently was produced in sufficient quantity and duration to prevent pigweed emergence without apparent harm to emerging cotton seedlings. The longevity of G. virens in the dried rice preparation and the ease with which it is stored and applied, suggest its possible use as a biological control agent to suppress pigweed in cotton plantings.