Wisconsin Potato and Vegetable Growers Association

Cucumber Downy Mildew Confirmed in SW Michigan

June 30th, 2020 | Posted in: Crop Updates, News

Updates provided by Amanda J. Gevens, Chair, Associate Professor & Extension Specialist, UW-Madison, Dept. of Plant Pathology

Downy mildew has been confirmed in southwestern MI (Berrien County) on cucumber on June 22. Because of our favorable weather (hot, frequent rain, humid), it is recommended that a preventative fungicide be applied to cucumbers. Several commercial programs, esp. for pickling cucumbers have included base protectants like chlorothalonil or mancozeb. These continue to be important tank mixes when you’re applying specialty fungicides that might be specific to water molds/oomycetes (like Phytophthora crown and fruit rot and downy mildew). This was a surprising find as there were no closer reports to us other than North Carolina over the past week.

Symptoms of downy mildew on cucurbits include distinctive pale green to yellow/brown in angular or vein-limited patches on leaf surfaces with accompanying gray to purple pathogen sporulation on leaf undersides. Pictures for reference can be found here: https://cdm.ipmpipe.org/photo-gallery-of-foliar-diseases-including-downy-mildew/

I provide a list of recommended fungicides, below, from Dr. Mary Hausbeck, Michigan State Univ. Her recent trials have demonstrated effectiveness of Previcur Flex, again, and so this is now back in the list of recommended treatments.

Also, please utilize our A3422 Commercial Vegetable Production Guide for Wisconsin for further information. In particular, see page 95 for cucumber downy mildew treatments. https://cdn.shopify.com/s/files/1/0145/8808/4272/files/A3422-2020.pdf

  • Ranman + chlorothalonil or mancozeb
  • Orondis Opti (chlorothalonil is part of the premix)
  • Elumin + chlorothalonil or mancozeb
  • Zampro + chlorothalonil or mancozeb
  • Previcur Flex + chlorothalonil or mancozeb*
    • *Note: Previcur Flex is back in the downy mildew fungicide recommendations for 2020 as it has been effective in the MSU research trials in 2018 and 2019. Prior to that, it had not been effective.

Since it’s not yet possible to predict whether this year’s downy mildew population will be controlled by Previcur Flex, be sure to use it as a tankmix with either chlorothalonil or mancozeb.

Please feel free to email or text pictures if you have any questions on symptoms. The UW Plant Disease Diagnostic Clinic is also open with mail access for physical samples.

Thank you,

Amanda Gevens
Chair, Associate Professor & Extension Specialist
Plant Pathology Department
1630 Linden Drive Room
University of Wisconsin-Madison
Madison, WI 53706

E-mail: [email protected]
Office: 608-890-3072/Cell: 608-575-3029

Potato & Vegetable Pathology Research and Extension
Website: https://vegpath.plantpath.wisc.edu/

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