Cucurbit Downy Mildew Report – July 11, 2014

Cucurbit downy mildew was confirmed in a central Michigan cucumber field on July 11, 2014.  The presence of downy mildew in the Great Lakes region means that Ontario cucumber crops are at a high risk of developing this disease. All growers are advised to maintain a 7-day fungicide program. Sprays are most effective when they are applied prior to a rainfall or irrigation event.

At this time consider switching to one of the targeted downy mildew fungicides, such as:

  • cyazofamid (Ranman 400SC, Torrent 400SC)
  • propamocarb/chlorothalonil (Tattoo C)
  • ametoctradin/dimethomorph (Zampro)
  • Fluopicolide (Presidio)

For more information, see OMAFRA publication 839, Ontario Vegetable Crop Protection Guide.

Scout fields regularly for signs of the disease.  Initial symptoms include a watery, bruise-like, angular lesion. Under humid conditions, fungal strands or spores may be noticeable on the lower leaf surface.  These spores are often difficult to see on fungicide-treated leaves.

water-soaked lesion
Cucurbit Downy Mildew – water-soaked lesion
spores on lower leaf surface
Cucurbit Downy Mildew – spores on lower leaf surface

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