Nitrogen (N) is the most important element that influences both vegetative growth and fruiting in cranberry production. While many factors such as cultivar, age and vigor of vines are important, soil fertility is one of the most important factors impacting yield and fruit quality. The high fertilizer N used to support increased yield potential of new cranberry second generation hybrids can result in increased vegetative growth, thus creating a dense canopy resulting in a microclimate with high relative humidity (RH). Humid conditions during the warm summer months encourage the expression of cranberry fruit rot (CFR). The goal of this study was to determine the effect of N application rate on CFR occurrence in ‘Stevens’ and ‘Mullica Queen’ at the UMass Cranberry Station in East Wareham, Massachusetts. To measure biophysical data, we deployed micro climatic sensors in each treatment to measure ambient temperature and RH. Four N rates were used ranging from 46 kg N ha-1 to 112 kg N ha-1 in a replicated RCBD experiment. Fruit samples were collected at harvest from each treatment and used to measure total anthocyanin content (TAcy) by extraction with 0.2 N HCL. Cranberry biomass in both cultivars increased with increase in N rate and so did fruit rot. Fruit yield increased with N rate up to a point then it started to decline as rate increased. High N rate of 112 kg N ha-1 was associated with a low canopy temperature, and high RH compared to 46 kg N ha-1 in both cultivars. Total anthocyanins in the fruit decreased with N rate in both cultivars. Our results seem to suggest that high N rate encourage fruit rot expression.
