Control of blue mold caused by Penicillium expansum on apples 'Empire' with fludioxonil and cyprodinil

Abstract

Penicillium expansum, one of the important causal agents of blue mold of apple in storages in Ontario, has developed resistance to thiabendazole, a postharvest fungicide, in some storages. In an attempt to develop alternate fungicides to thiabendazole, the protective effect of three fungicides, fludioxonil, cyprodinil, and a mixture of fludioxonil and cyprodinil, were evaluated for their efficacy against blue mold caused by thiabendazole-sensitive and -resistant isolates of P. expansum. The three fungicides were equally effective against thiabendazole-sensitive and -resistant isolates of P. expansum. Fenhexamid had no activity against P. expansum. No cross-resistance was observed between thiabendazole and fludioxonil or cyprodinil. Lower concentrations of fludioxonil (45 µg·mL–1), cyprodinil (50 µg·mL–1), and fludioxonil + cyprodinil (50 + 75 µg·mL–1) gave >97.0% control for up to 1 month, but higher concentrations of fludioxonil (100 µg·mL–1) and fludioxonil + cyprodinil (150 + 225 µg·mL–1) were required to control blue mold for 62 days at 4 °C. When the mixture was tested, antagonistic effect was observed at lower concentrations; however, higher concentrations completely controlled the disease. Fludioxonil and cyprodinil have modes of action different from each other and from that of the thiabendazole; they have the potential to be effective components in the resistance management for postharvest control of apple blue mold.