Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu
Cucumber growers should monitor their crops for downy mildew. Symptoms of downy mildew on cucumber are angular yellow to tan lesions on the upper surface of the leaf and brown to black sporulation on the lower surface.
Downy mildew was found a second time last week in North Carolina on greenhouse grown cucumbers. This outbreak may have started two months ago. Although there are no reports north of the Carolinas, it is extremely troubling that downy mildew is present there so early in the season. Growers should scout their fields and monitor the Cucurbit Downy Mildew ipmPIPE site http://cdm.ipmpipe.org/ for the progress of the disease. Preventative fungicide applications should begin when disease occurrence is predicted in our region.
Downy mildew on cucumber leaf. Angular necrosis on upper leaf surface and dark sporulation on lower leaf surface.