Confirmed reports of cucurbit downy mildew. https://cdm.ipmpipe.org
Downy mildew developed in a commercial fresh market cucumber field in Huron County this past weekend. That makes five counties in northern Ohio with confirmed reports of downy mildew, all on cucumbers. It is likely that downy mildew is widely distributed in cucumbers in northern Ohio, but we are not always alerted to its appearance. Since our first report of downy mildew on cucumbers in Wayne County on July 13, it has been reported in several other fields, including one of our research plots in Wooster. So far there are no confirmed reports of downy mildew on melons, pumpkins, squash or other cucurbits in Ohio.
Downy mildew must be managed preventatively with resistant varieties (there are a few, see chart below) and more commonly with fungicides. In our experience, fungicides applied after infection are significantly less effective than the same ones applied before infection. Cucumber and melon growers in northern Ohio should be applying effective fungicides on a 5-7 day schedule depending on the label requirements. Growers elsewhere in the state should be applying protectants such as chlorothalanil, e.g. Bravo, to all cucurbits. This will also help prevent other diseases such as Alternaria leaf spot and gummy stem blight. More details and a fungicide efficacy table can be found here.
