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Increased Incidence of Pythium Stem Rot in Cowpeas Treated with Benomyl and Related Fungicides. R. J. Williams, Plant Pathologist, Grain Legume Improvement Program, International Institute of Tropical Agriculture, P.M.B. 5320, Ibadan, Nigeria; Abateni Ayanaba, Soil Microbiologist, Farming Systems Program, International Institute of Tropical Agriculture, P.M.B. 5320, Ibadan, Nigeria. Phytopathology 65:217-218. DOI: 10.1094/Phyto-65-217.

In six replicated field trials during a 3-year period the incidence of cowpea wet stem rot caused by Pythium aphanidermatum was significantly greater in plots treated with benzimidazole (BZ) fungicides than in plots treated with non-BZ fungicides and nontreated plots. In laboratory studies, the growth of P. aphanidermatum in corn-meal agar was unaffected by the addition of up to 250 µg/ml active ingredient of the BZ fungicides. It seems likely that the broad-spectrum, yet selective, BZ fungicides favor the activity of P. aphanidermatum by suppressing antagonists and competitors.