Downy mildew was reported today in Gratiot County, MI on cucumbers. We have not found downy mildew on cucumbers, melons or any other cucurbit crops yet in Ohio, but it is likely to be in some fields in the northern third of the state. There are a couple of diseases out there that look like downy mildew – angular leaf spot, a bacterial disease, and anthracnose, caused by a fungus, can cause some confusion and shown up in Ohio cucumbers this season. See the photos below. The third photo is of downy mildew on cucumber. See my July 3, 2014 post for management recommendations for downy mildew.
Angular leaf spot on squash
Anthracnose on cucumber
Downy mildew on cucumber