Response of Pseudoperonospora cubensis to Preventative Fungicide Applications Varies by State and Year

Abstract

In bioassays on cucumber (Cucumis sativus) in New York, Ohio, and South Carolina in 2015 and 2017, mandipropamid (Revus) and azoxystrobin (Quadris) failed to suppress downy mildew caused by Pseudoperonospora cubensis. Propamocarb (Previcur Flex), cymoxanil + famoxadone (Tanos), and fluopicolide (Presidio) were ineffective in one or two states in both years. Famoxadone, dimethomorph (Forum), cymoxanil (Curzate), and mancozeb (Manzate) were ineffective in one state one year. Oxathiapiprolin, cyazofamid (Ranman), and fluazinam (Omega) suppressed downy mildew in 380% of the bioassays.