Control of rhizopus rot of peaches with postharvest treatments of tebuconazole, fludioxonil, andPseudomonas syringae

Rhizopus rot caused by Rhizopus stolonifer is a potentially serious postharvest disease of Canadian-grown peaches. Several new fungicides are effective against brown rot (Monilinia fructicola) of peaches, but little is known of their postharvest efficacies against R. stolonifer. Harvested peaches were arranged in trays, individually punctured once and co-treated with a suspension of both R. stolonifer sporangiospores and cells of an isolate of Pseudomonas syringae or one of 13 fungicides at 0.5–1.0 times the dilute concentration used to control brown rot in orchard programs. In subsequent experiments, the peaches were inoculated with R. stolonifer, incubated for 6 h, chilled, and a day later the inoculated sites were brushed with a suspension of fludioxonil, tebuconazole, or P. syringae. In the co-treatment studies, azoxystrobin, fenhexamid, fenbuconazole, myclobutanil, benomyl, and sulfur reduced rhizopus rot by 0–22%. Cyprodinil and propiconazole gave 20–60% reduction, while fludioxonil, tebuconazole, and two P. syringae isolates gave 75–100% reduction, comparable with that of dicloran and iprodione. Post-inoculation brushing treatments with P. syringae at 10 000 µg ESC 10/mL gave less than 20% control, while fludioxonil and tebuconazole gave 90% control (EC90) at 472 and 718 µg/mL, respectively.