Evaluating Fungicide Inputs and Their Impact on Losses from the Cranberry Fruit Rot Complex

Cranberry fruit rot (CFR) is a complex of fungal pathogens affecting a long-lived perennial crop and is managed primarily through repeated, in-season fungicide applications. Because cranberries are grown in the same beds for decades, CFR is considered a disease system in which the inoculum may accumulate across years, suggesting the potential for multiyear management strategies that reduce fungicide inputs. This multiyear field study evaluated whether fungicide inputs could be reduced without increasing disease losses by using existing disease-forecasting tools or implementing systematic multiyear fungicide-reduction strategies. Treatments included forecast-driven spray programs based on the Massachusetts Keeping Quality Forecast and a cranberry canopy microclimate model, systematic multiyear reductions, and alternating-year fungicide programs using both multisite and reduced-risk fungicides. Under high disease pressure in New Jersey, reduced fungicide inputs consistently increased fruit rot incidence and yield loss. Fruit rot severity closely reflected fungicide inputs applied within the same season, with little to no consistent carryover benefit from prior-year fungicide programs. Multisite fungicides provided superior disease control compared with reduced-risk, single-site fungicides, although yields in reduced-risk treatments were higher than expected given observed disease levels. Physalospora vaccinii was the predominant species isolated from rotted fruit in the years of this study, and fungicide treatments had a minimal impact on pathogen species composition. These findings indicate that CFR epidemics are driven primarily by within-season infection events and that reducing fungicide application frequency below standard programs is likely to result in unacceptable disease losses under high disease pressure.