Year-to-Year Incidence of Cranberry Fruit Rot and Persistence of Fungal Pathogens

Cranberry fruit rot is a disease complex comprised of as many as 15 fungal species. Current management recommendations are to spray broad-spectrum fungicides every year in regions such as New Jersey where fruit rot incidence is high on a consistent basis. By contrast, in regions such as Wisconsin, where economic losses from fruit rot occur sporadically, many growers forego fungicide sprays, but if faced with a serious fruit rot outbreak they then spray fungicides intensively the following year to prevent a recurrence of disease. This recommendation is based on the untested assumption that left unchecked, fruit rot incidence will increase and that the predominant fruit rot pathogens will persist from one year to the next. Field studies conducted over 3 years showed that in New Jersey fruit rot incidence increased or remained high and fruit rot pathogens persisted from one year to the next. By contrast, in Wisconsin fruit rot incidence decreased or remained low, and the persistence of pathogens was inconsistent from one year to the next. Thus, in Wisconsin, fruit rot incidence and fungal species present in one year do not reliably predict the disease situation in the following year, a finding that should be considered when planning fungicide spray programs.