Cucumber downy mildew was found today in Berrien County in southwest Michigan. This is the first report of cucurbit downy mildew this year in the Great Lakes region. The pathogen was detected in spore traps in Berrien County June 8, 10, and 13, and in Muskegon County on June 8. Dr. Mary Hausbeck has provided details of the outbreak and a link to the spore trap data here.
This is relatively early for cucumber downy mildew in Michigan and Ohio – we often see it around the 4th of July and last year it appeared weeks later. Humid, rainy, cool to warm weather favors this disease. It is likely that downy mildew will be in Ohio soon, especially the northern counties, if it is not already here. Cucumber growers in the northern third of the state should begin a downy mildew fungicide program immediately. Dr. Hausbeck recommends a rotation of the following fungicides tanked mixed with chlorothalanil or mancozeb: Ranman, Elumin, Zampro, Previcur Flex, or Orondis Opti (no need to tank mix Orondis Opti since it is a premix with chlorothalanil). Make sure to check the labels for use restrictions and preharvest intervals (PHIs).
The Michigan recommendations are based on 2019 field evaluations of these fungicides. Our Ohio bioassay evaluations in 2019 had similar results, although we did not test Previcur Flex.
You can follow reporting of cucurbit downy mildew outbreaks in the US on the CDM ipmPIPE website. This website was revamped this year and if you want to receive alerts of downy mildew outbreaks you will need to sign up, even if you had signed up on the previous website.
If you think you have downy mildew in cucumbers or other cucurbits on your farm or in your home garden, you can send samples to the OSU Vegetable Pathology Lab for a free diagnosis.