July 6th, 2020 – Downy Mildew was identified today in a commercial cucumber field in Kent County, Ontario. The disease had previously been identified in the Great Lakes area, in Michigan on June 22nd. Growers were advised to use a downy mildew specific fungicide program once the disease was found in the Great Lakes area. Risk remains high now that the disease has been confirmed in Ontario despite hot, dry weather.
As noted in our previous post, trials in Michigan and Ontario have shown that the three most consistently effective downy mildew fungicides are Orondis Ultra, Torrent and Zampro. Where possible, it is important for resistance management for these products to tank mix each application with chlorothalonil or mancozeb. In addition to tank mixing to delay resistance development, never make back-to-back applications of products from the same chemical family. Follow a 5 to 7-day application interval, and rotation of the three products can be repeated as necessary.
Cucumbers are most at risk, but cantaloupe growers should be aware that downy mildew that infects cucumbers is also a risk. See crop labels for listed cucurbit crops registered on the products below.
If you suspect downy mildew in your field, send for confirmation immediately. Contact either OMAFRA specialist listed below if you have any questions about detection or management.
Katie Goldenhar, Pathologist—Horticulture, firstname.lastname@example.org, 519-835-5792
Andrew C. Wylie, Vegetable Crop Specialist (A), email@example.com, 519-401-5890