Specific Tolerance of Sclerotium cepivorum to Dicarboximide Fungicides. E. R. Littley, Research Assistant, Centre for Pest Management, Simon Fraser University, Burnaby, BC, Canada V5A 1S6. J. E. Rahe, Associate Professor, Centre for Pest Management, Simon Fraser University, Burnaby, BC, Canada V5A 1S6. Plant Dis. 68:371-374. Accepted for publication 28 October 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/PD-68-371.

Five isolates of Sclerotium cepivorum tolerant to one dicarboximide fungicide showed cross-tolerance to the dicarboximides iprodione, myclozolin, and vinclozolin and to dicloran and PCNB but not to benomyl, captan, or thiram. The dicarboximides dicloran and PCNB share a common structural subunit. EC₉₀ values for most tolerant isolates were >1,000 times those of the parent isolates. Sensitivity to benomyl was unchanged by tolerance to dicarboximides. Wide variations in sensitivity of the parent isolates to PCNB and thiram were noted. Frequency of occurrence of dicarboximide tolerance was too low and variable to obtain a reliable estimate.