Resistance of Venturia inaequalis to Benomyl and Dodine in British Columbia, Canada. P. L. Sholberg, Agriculture Canada Research Station, Summerland, British Columbia V0H 1Z0, Canada. J. M. Yorston and D. Warnock. British Columbia Ministry of Agriculture and Fisheries, Kelowna, British Columbia V1Y 4R2, Canada. Plant Dis. 73:667-669. Accepted for publication 13 February 1989. Copyright 1989 Department of Agriculture, Government of Canada. DOI: 10.1094/PD-73-0667.

An initial survey of 28 orchards in British Columbia in 1986 identified resistance of Venturia inaequalis to benomyl in nine orchards and also indicated some resistance to dodine in eight orchards. In 1987 samples of the apple scab fungus were collected from 145 orchards and tested for resistance to benomyl and dodine. Conidia from 54.3% of all 173 orchards were resistant to dodine at 2.0 µg/ml, conidia from 25.4% of the orchards were resistant to benomyl at 1.0 µg/ml, and conidia from 20.8% were resistant to both fungicides. The geographic distribution of resistance was consistent with pesticide use patterns. Resistance was most common in the wetter northern area of the Okanagan Valley, where benomyl has been used since 1973 and dodine since 1961. No resistance was evident in southern areas of the Okanagan Valley, where the climate is drier and apple scab is of much less economic importance. On the other hand, the four samples from the Victoria area of Vancouver Island, which has a wet, coastal climate, were all resistant to benomyl, and three samples were also resistant to dodine. Benomyl has been widely used to control apple scab in this area, but dodine has had minimal use there in recent years because of problems with fruit russeting.