We confirmed downy mildew in cucumbers collected yesterday from a small commercial field in Belmont County, near Barnesville. Disease incidence and severity were high in this field, which had not been treated with any fungicides. The outbreak followed several days of intense rainfall in the previous week.
Map of cucurbit downy mildew outbreaks – CDM ipmPIPE, July 26, 2017.
This is the first report of cucumber downy mildew in central or southern Ohio, and was found during a field walk sponsored by OSU Extension and the Captina Produce Auction. Ohio growers should assume that cucumber/melon downy mildew is more widespread than we have been able to report, and should protect these crops with appropriate fungicides as listed in my post on July 28. We have not seen downy mildew on squash, pumpkins or watermelon in Ohio to date, and the downy mildew pathogen population currently affecting cucumbers and melons in Ohio is not likely attack pumpkins or squash. A pumpkin field near the cucumber planting that was highly diseased was not affected, and we have not found downy mildew in our sentinel plots, despite the presence of infected cucumbers for several weeks. However, downy mildew populations that can damage pumpkins and squash are likely to move in from the southeastern U.S. later in the season.
We depend on county educators, growers and consultants to let us know when cucurbit downy mildew is suspected, particularly in counties where it has not been reported. Our lab will diagnose samples at no cost to Ohio growers, so we appreciate receiving samples that, if downy mildew is confirmed, will enable us to alert the cucurbit growing community.