Sensitivity of Penicillium spp. and Botrytis cinerea to pyrimethanil and its control of blue and gray mold of stored apples

Twenty-one Botrytis cinerea and 22 Penicillium spp. isolates were evaluated for sensitivity to pyrimethanil. Fungicide sensitivity was determined by measuring mycelial growth on agar medium amended with pyrimethanil. The mean EC50 values for B. cinerea and Penicillium spp. were 0.039, and 0.331 μg ml−1, respectively. The subset of 17 P. expansum isolates had a mean EC50 value of 0.314 μg ml−1 ranging from a low value of 0.054 to a high value of 0.566 μg ml−1. Preharvest application of pyrimethanil at 800 μg ml−1, applied 20 days before harvest on 29 September, 1999 controlled postharvest blue and gray mold on wounded and inoculated 'Jonagold' apples after storage in air at 1 °C for 6 months. Similarly, pyrimethanil at 800 μg ml−1 in 2000, and 600 μg ml−1 in 2001, applied 2 weeks before harvest in each year controlled blue and gray mold on 'Gala' apples stored for 6 months. Pyrimethanil applied at rates ranging from 250 to 1000 μg ml−1 after harvest to wounded 'Gala' apples inoculated with conidia of B. cinerea and thiabendazole-resistant P. expansum, completely prevented any blue or gray mold decay. Pyrimethanil is an important new fungicide for control of both blue and gray mold decay of apples that can be applied either before or after harvest.