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.