Postharvest Fungicides for Apples: Development of Resistance to Benomyl, Vinclozolin, and Iprodione. D. A. Rosenberger, Assistant Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Hudson Valley Laboratory, Highland 12528. F. W. Meyer, Research Technician, Department of Plant Pathology, New York State Agricultural Experiment Station, Hudson Valley Laboratory, Highland 12528. Plant Dis. 65:1010-1013. Accepted for publication 17 February 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-1010.

The mean incidence of vinclozolin-resistant and iprodione-resistant spores from four isolates of Penicillium expansum was 1.96 × 10^–5 and 1.71 × 10^–6, respectively. All of 25 isolates tested that were resistant to iprodione were also resistant to vinclozolin. However, only 9 of 16 isolates that were resistant to vinclozolin were also resistant to iprodione. In a postharvest fungicide test with McIntosh fruit, two wild-type isolates were more pathogenic than the two isolates resistant to vinclozolin and the two resistant to iprodione. Mean incidence of decay in fruit not treated with fungicides was 65% for wild-type isolates compared with 0.4% for isolates resistant to vinclozolin and iprodione. Benomyl and CGA 64251 were effective against all these isolates.

Keyword(s): cross-resistance, fungicide resistance.