ASHS 2025 Conference

The American cranberry (Vaccinium macrocarpon Aiton), commonly known as the large-fruited cranberry, is native to North America. Fruit quality remains a major challenge for cranberry growers, with the cranberry fruit rot (CFR) complex posing a significant threat. Cranberry fruit rot is associated with over a dozen taxonomically diverse fungi. In the northeastern United States, growers typically apply three to five fungicide treatments per growing season to manage CFR. Even with well-timed applications, growers often observe rot levels between 1% and 15%, or sometimes higher. When rot exceeds 12%, growers face financial penalties, and crops with more than 20% rot are often rejected by processors. Managing CFR has become increasingly difficult, particularly in high-yielding and newer cultivars. This challenge is further compounded by regulatory restrictions over the past decade on key fungicides such as chlorothalonil and mancozeb. As conventional control options decline, interest in alternative strategies continues to grow. However, the influence of microclimate, cultural practices, and plant physiological factors on CFR incidence and overall fruit quality remains poorly understood. In this study, we investigated 22 cranberry bogs in Massachusetts over a three-year period (2021–2023) to elucidate the relationships among weather variables (temperature, humidity, growing degree days [GDD], soil moisture), plant traits (fruiting upright-to-total upright ratio, leaf area index [LAI], canopy height), cultural practices (fungicide choice and frequency), and fruit quality metrics (rot incidence, yield, anthocyanin content, and firmness). Statistical analyses included year-to-year comparisons, predictor-response modeling, and time-series evaluations to identify critical periods influencing fruit quality outcomes. Key findings indicate that interannual microclimatic variation significantly affects fruit quality. Temperature influenced anthocyanin accumulation throughout the growing season, while GDD accumulation influenced fruit yield. A higher fruiting upright ratio was associated with increased yield and firmness, while greater LAI correlated with higher anthocyanin content. Although fungicide choice and application frequency varied widely among participating bogs, a marked reduction in fruit rot and an increase in yield were observed with up to four fungicide applications; however, additional applications beyond this threshold did not result in further significant improvements. Notably, bog age did not have a significant effect on fruit quality. These findings highlight the need for integrated, site-specific strategies that combine environmental monitoring with targeted interventions to improve cranberry production and support long-term sustainability.