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Influence of Sequential Dew Periods on Biocontrol of Sicklepod (Cassia obtusifolia) by Alternaria cassiae. H. L. Walker, Research Plant Pathologist, Southern Weed Science Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Stoneville, MS 38776. C. D. Boyette, Research Plant Pathologist, Southern Weed Science Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Stoneville, MS 38776. Plant Dis. 70:962-963. Accepted for publication 4 April 1986. 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, 1986. DOI: 10.1094/PD-70-962.

In greenhouse tests, at least 8 hr of dew within 2 days after inoculation was required for the fungus Alternaria cassiae to kill all inoculated sicklepod seedlings consistently. Increased efficacy of A. cassiae was evident when inoculated seedlings were treated with two shorter than optimal dew periods of 26 hr 1, 2, 3, or 4 days after the initial dew period. For A. cassiae to be used as a microbial herbicide, inoculum should be applied when environmental conditions are favorable for dew to occur on the foliage of sicklepod within 2 days after inoculation.