Assessment of fungicide product applications and program approaches for control of downy mildew on pickling cucumber in North Carolina

Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew (CDM), is the most economically devastating and widespread disease of cucurbitaceous crops in the Eastern United States (US). Cucumbers are particularly susceptible and as a result, disease management of P. cubensis relies heavily on fungicide use. The re-emergence of P. cubensis in the US in 2004 resulted in the failure of previously effective host resistance and the pathogen has become less sensitive to several fungicides, limiting the efficacy of crop protection. The implementation of effective spray programs is recommended to minimize the development of fungicide resistance in pathogen populations. However, few studies have examined annual efficacy trials to generate robust recommendations. To determine the efficacy of fungicide applications on CDM in pickling cucumber regarding disease severity and marketable yield, field experiments were conducted from 2013 to 2016 in North Carolina. Evaluations included single-product fungicide applications as well as program treatments on susceptible cultivars. Although there was some variability between years due to differences in products applied, our analysis revealed that several single-site treatments were effective in the suppression of disease, including treatments that included oxathiapiprolin, cyazofamid, propamocarb, ethaboxam, fluazinam, and a mixture of mancozeb/zoxamide. Additionally, when compared to the non-treated controls, spray programs that included tank mixes with protectants and alternations of fungicide modes of action, resulted in lower levels of downy mildew and increased marketable yield.