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Potency of difenoconazole against nine postharvest pathogens of pome fruit

Achour Amiri: Washington State University

<div>Difenoconazole (DFC) was registered as a postharvest fungicide pre-mixed with fludioxonil in 2016. Herein, we report on the efficacy of DFC against <em>Penicillium expansum </em>(Pe), <em>Botrytis cinerea </em>(Bc), <em>Neofabraea perennans </em>(Np), <em>Alternaria alternata </em>(Aa), <em>Mucor piriformis </em>(Mp), <em>Lambertella corni-maris </em>(LCM), <em>Sphaeropsis pyriputrescens </em>(Sp), <em>Phacidiopycnis washingtonensis </em>(Pwa) on apple and <em>Phacidiopycnis pyri</em> (Pp) on pear. Non-wounded Fuji apples and d ’Anjou pears were inoculated with spore suspensions at 5 x 10<sup>4</sup> spores/ml at an experimental orchard prior to harvest for all pathogens except Pe, Mp, and LCM<em>, </em>which were inoculated post-harvest on wounded fruit. Orchard-inoculated fruit were harvested 10 days post-inoculation and treated by dipping for 1 min in a DFC (Thesis) suspension at 0.3 g/liter, whereas wounded fruit used for Pe, Mp, and LCM were treated preventively with DFC and inoculated 4h post-treatment. Four replicates of 20-fruit each was used for each pathogen and fruit were stored for 6 months at 1°C in a regular atmosphere to determine disease incidence and severity. DFC applied curatively controlled Pwa, Pp, Sp and Aa effectively after 6 months of storage whereas a moderate efficacy was observed for Bc and Np. Preventive DFC application provided a high efficacy against Pe and LCM but not Mp. The high DFC potency against most postharvest pome fruit pathogens observed indicates the fungicide would be an effective tool in future management programs.</div>