Downy mildew was confirmed on cucumbers in two additional Ohio counties late last week: Harrison and Licking. We still have not confirmed downy mildew on pumpkins or squash in any part of Ohio. On today’s Cucurbit Downy Mildew ipmPIPE conference call, none of the representatives from nearby states (MI, WV, VA) reported seeing downy mildew on pumpkins or squash yet this season. However, downy mildew has been reported recently on jack-o-lantern pumpkins in two counties in northwestern Indiana. Careful scouting of pumpkin and squash fields should remain a priority.
Downy mildew can be confused with powdery mildew at very early stages of the latter (before the white powdery colonies appear), especially if the pale yellow areas on the top of the leaves are very dense. Symptoms of other diseases including angular leaf spot and bacterial spot can also be confused with those of downy mildew. If in doubt, please send a sample to your county educator or directly to the OSU Vegetable Pathology Lab in Wooster, OSU-OARDC, 1680 Madison Ave., Wooster, OH 44691; ph. 330-263-3838.
We are in the process of evaluating commercially available fungicides for efficacy against downy mildew using a bioassay. We will have results within a few weeks. However, we are not aware of new fungicide failures in other parts of the US this season, so our fungicide recommendations posted on June 28, 2017 remain in place.