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Effect of Benomyl on Sclerotinia Crown and Stem Rot of Alfalfa. Ronald E. Welty, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, Oxford, NC 27565. John O. Rawlings, Professor, Department of Statistics, North Carolina Agricultural Research Service, Raleigh 27650. Plant Dis. 68:294-296. Accepted for publication 20 September 1983. 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/PD-68-294.

Benomyl at 560 g a.i./ha was applied once, twice, or monthly beginning in October 1974 and ending in February 1975. Symptoms of crown and stem rot of alfalfa (Medicago sativa) were first observed in January, and diseased areas increased until the middle of March. The most effective spray schedule was monthly; the most effective single spray was in December. Benomyl applied as a protectant suppressed the severity of crown and stem rot; benomyl applied after symptoms appeared did not retard the spread of the disease. This study shows that one application of an effective fungicide provides control of crown and stem rot. However, yearly variations in temperature and rainfall influenced subsequent experiments, and it was not established that a single application of benomyl in December can be applied regularly to seedling alfalfa to prevent crown and stem rot. More research is needed to relate the appearance of apothecia to fungicide application.

Keyword(s): Sclerotinia trifoliorum.