We have confirmed downy mildew on pumpkins for the first time in Ohio this year, in Pike County. Downy mildew is widespread in northern Ohio on cucumbers and melons, but has not been reported on pumpkins, squash or watermelon in this area to date. The Pike County report of downy mildew on pumpkins comes less than 2 weeks after it was reported on processing pumpkins in Illinois. The only way to control this disease is through the use of effective fungicides, applied preventatively. Once the disease becomes obvious in a field, it may be too late to get good control. Whether or not downy mildew should be controlled on pumpkins as we enter into September and later is up to the grower. The disease does not cause symptoms on fruit, so if pumpkins are at or near the stage to be harvested, it may not be necessary to apply fungicides. If fungicides are to be used, we recommend Orondis Opti alternated with Ranman, Zing! or Zampro (tank mixed with a protectant fungicide like chlorothalanil or mancozeb if not included in the product). We are also finding bacterial spot on pumpkins, so growers should confirm downy mildew before applying these fungicides.
Downy mildew symptoms on a pumpkin leaf.