Evaluating foliar fungicide efficacy, sensitivty and persistence to improve management of wild blueberry (Vaccinium spp.) foliar diseases

Abstract

Wild blueberry foliar pathogens Thekopsora minima and Sphaerulina vaccinii, indirectly reduce wild blueberry yields. Determining alternative fungicide options for wild blueberry growers is required due to deregistration of chlorothalonil in Canada. Field trials in 2021 discovered plants treated with prothioconazole + benzovindiflupyr had 49% less mean disease compared to the untreated, and 17% greater mean leaf number than all other treatments. In vitro fungicide sensitivity was assessed by calculating the effective concentration which inhibits fungal growth by 50% (EC50). The prothioconazole-desthio EC50 for S. vaccinii was significantly lower than all other fungicides. Benzovindiflupyr was highly effective at inhibiting T. minima urediniospore germination, with EC50 being 98% lower than other fungicides. Fungicide residue in leaf tissues were assessed 0, 7, 14 and 30 days after application using GC-MS and LC-MS. Thirty days after application, fungicides were still detected, with benzovindiflupyur being detected at the greatest concentration, with pydiflumetofen, mefentrifluconazole and prothioconazole-desthio in decreasing concentration. The results from this study outline fungicides that can effectively manage foliar pathogens at a field scale, how fungicides inhibit fungal growth in-vitro for these two predominant pathogens and the duration of these fungicides within the leaf tissue. These results can help guide fungicide selection and application timing decisions within the wild blueberry industry.