Cucumber Downy Mildew Spreading

Map of 2023 cucurbit downy mildew reports. Red = reported <1 week ago; Green = reported > 1 week ago.

Downy mildew is now confirmed in cucumbers in five Ohio counties: Sandusky, Fulton, Medina, Wayne and Knox. The latest report, from Sandusky County, was from our sentinel plot on OSU’s North Central Agricultural Research Station (NCARS) in Fremont. Our interns Raven and Audrey scouted the week before and saw no symptoms or signs of downy mildew. One week later, downy mildew symptoms and signs were present on leaves of every cucumber plant in the sentinel plot (see photos).  This illustrates the explosive potential of this disease on a highly susceptible host like cucumbers and the necessity

Downy mildew on cucumbers in the OSU Sentinel plots at NCARS, Fremont, OH, July 24, 2023. Photo by R. Schaffter.

Underside of cucumber leaf showing downy mildew lesions and signs of the pathogen, Pseudoperonospora cubensis. NCARS, July 24, 2023. Photo by Raven Schafter.

of managing it preventatively.  This is mainly done through applications of appropriate bound spectrum fungicides such as chlorothalanil and mancozeb plus specific fungicides (e.g. Orondis Opti, Elumin, Ranman) targeted against the downy mildew pathogen and other oomycete pathogens. See previous recent posts on management tactics for cucurbit downy mildew.

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