A Mummy Berry Update from Northwestern Washington Blueberry Fields: Spore Trapping and Assessing the Sensitivity of Monilinia vaccinii-corymbosi to DMI Fungicides

Mummy berry, caused by Monilinia vaccinii-corymbosi (Mvc), is a disease characterized by blighted young shoots and flower clusters, and mummification of fruits in blueberry (Vaccinium corymbosum), resulting in economic losses. To monitor the timing of primary inoculum (ascospore) release from apothecia, rotating-arm air samplers were deployed in a northern highbush blueberry field in Whatcom County of northwestern Washington during the 2022, 2023, and 2024 production seasons. Mvc was detected and quantified via a quantitative real-time PCR (qPCR) using species-specific primers. To complement these data, field observations on host and pathogen phenology were recorded from February to April in all three study years. While qPCR results aligned with visual observations of apothecia formation on mummified berries in the field, use of air samplers did not result in earlier detection of primary inoculum compared to visual observations during the study period. In parallel, 64 Mvc isolates were obtained from blueberry fields with mummy berry across five Washington counties during 2021 and 2022. These isolates were evaluated with mycelial growth inhibition assays for their sensitivity to fenbuconazole and metconazole fungicides, which are commonly used to manage mummy berry. All tested isolates exhibited EC50 values less than 0.08 µg/ml for both fungicides, indicating their in vitro efficacy.