Cucurbit Downy Mildew Update

DM Map 9Aug2016-2

Counties in which downy mildew has been reported on cucurbits. Most recent outbreaks are in red. Map from

So far downy mildew has been confirmed on cucumbers in Wayne, Huron, Sandusky, Medina, and Fulton counties in Ohio. We also found it on cantaloupe in our sentinel plots in Huron County on July 28. We have not had reports of downy mildew on squash or pumpkins in Ohio to date. With dry or very dry weather in much of Ohio (1/3 of Ohio is currently under moderate drought conditions), we expect that downy mildew will continue to be less frequent and less severe than in previous years. However, in gardens and fields where it has occurred and fungicides have not been applied, downy mildew has been very damaging.  We are recommending Orondis Opti alternated with Ranman, Gavel, Zing! or Zampro (tank mixed with a protectant fungicide like chlorothalanil or mancozeb if not included in the product). Presidio has been an effective fungicide in the past, but several studies have shown that it has lost efficacy in the last few years. Growers should be aware, especially with pumpkins, of other diseases that may be confused with downy mildew. Bacterial spot of pumpkin can cause leaf spots that converge and kill the leaves; however, fungicides are ineffective against bacterial spot. Despite the dry weather, we have seen bacterial spot of pumpkin and other bacterial diseases of vegetable crops this year in Ohio. Bacterial diseases are best managed in vegetables by using clean seed and reducing bacterial populations during transplant production by limiting moisture and applying bactericides.


Bacterial spot symptoms on pumpkin leaf.


Downy mildew symptoms on pumpkin leaf.



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