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A Benzimidazole Resistant Strain of Erysiphe graminis. J. M. Vargas, Jr., Assistant Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823; Phytopathology 63:1366-1368. Accepted for publication 28 April 1973. DOI: 10.1094/Phyto-63-1366.

A strain of Erysiphe graminis suspected of being resistant to benomyl was removed from a benomyl-treated field plot of Poa pratensis ‘Merion’. This strain was compared with a common (benomyl-susceptible) strain of E. graminis for sensitivity to 4 different systemic fungicides, thiabendazole, thiophanate-methyl, triarimol and benomyl. The fungicides were applied as drenches in one or two 50 ml applications/replicate of potted P. pratensis Merion at concentrations of 50, 100, 500, and 1,000 µg/ml (active ingredient). The plants were then inoculated either with the suspected benzimidazole resistant strain (BRS), or with a common benzimidazole susceptible strain (BSS). The BRS of E. graminis proved resistant to benomyl, thiabendazole and thiophanate-methyl through one application of the 1,000 µg/ml rate, but was sensitive to two applications of benomyl and thiophanate-methyl at 1,000 µg/ml rate, a rate that was phytotoxic to the plants. The BSS, on the other hand, was eliminated by benomyl, thiabendazole and thiophanate-methyl after one application of 100 µg/ml. Triarimol controlled both the BRS and BSS with one application of 50 µg/ml.