We have just reported to the Cucurbit Downy Mildew ipmPIPE the first case of downy mildew on cucumbers in Wood County. While the sample was just received today, the grower estimated that symptoms were first present July 7, about a week after the first report of downy mildew on cucumbers upwind in southeastern Michigan. The multiple rainstorms last week likely delivered the downy mildew pathogen from long distances and also moved it about locally, while the overcast, humid conditions favored pathogen survival and infection. Although predicted weather patterns for this week in northern Ohio are not as favorable for downy mildew as last week, growers should assume the pathogen is present and take or continue measures to protect cucumbers and melons from downy mildew. We have not yet found or had reports of downy mildew in central or southern Ohio on any crops, and no reports of the disease on squash, pumpkins, cantaloupe or watermelon in northern Ohio. That being said, cantaloupe is second to cucumber in susceptibility to downy mildew, and should be protected by fungicides in this area. See my posts on June 28 and July 8 for more information on cucurbit downy mildew management.
Single lesion of downy mildew on cucumber leaf from Wooster sentinel plot.
We also found downy mildew at a very early stage of development in our sentinel plot in Wooster today (see photo). There were only a few lesions present and it took a keen eye to spot them. When scouting for downy mildew in cucumbers, look for this type of early lesion. If the diseases progresses significantly it will be difficult to avoid yield losses despite fungicide applications.
If you suspect downy mildew in any cucurbit or basil, please send us a sample for confirmation. It is best if the sample is wrapped lightly in a damp paper towel and shipped in a box by overnight mail or courier to: Sally Miller, OSU-OARDC, Dept. Plant Pathology, 1680 Madison Ave, Wooster, OH 44691; 330-466-5249.