Downy mildew has still not been confirmed on pumpkins and squash in Ohio, although the disease is widespread on cucumbers and melons throughout most of the state. This is the time of year when we really start to look for downy mildew on squash and pumpkins, as strains of the pathogen that attack these crops move into the area from the south, usually aided by remnants of hurricanes or tropical storms that reach Ohio. Remnants of tropical storm Harvey are likely to reach southern Ohio at least by Friday. Downy mildew spores can be transmitted long distances in the air, and are brought to the surface by rain. We are particularly concerned with outbreaks reported in Kentucky on butternut squash this week (http://cdm.ipmpipe.org/scripts/map.php), an indication that the pathogen is established in the area and can serve as a source of inoculum for areas to the north and east. Growers in southern Ohio should be especially vigilant, although we recommend stepped-up scouting of pumpkins and squash, and application of protectant fungicides, throughout the state. Fungicide recommendations can be found in my June 28 post.
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.
Downy mildew continues to take a toll on cucumbers and melons throughout the state. We have numerous reports of downy mildew on these two crops from northern and central Ohio, with new observations confirmed yesterday in Hardin and Greene counties. Downy mildew is best managed by preventative fungicide applications – a list of effective fungicides can be found in my June 28, 2017 post.
We still have not confirmed downy mildew on pumpkins or squash anywhere in Ohio. However, downy mildew has been reported on butternut squash in Blair County in central PA, and on jack-o-lantern pumpkins in Starke County, in northwestern IN. It is a good idea to scout all cucurbits if you have not yet seen downy mildew in your area, and maintain a protectant fungicide program. Keep in mind that on squash and pumpkins, powdery mildew can look like downy mildew in the early stages before the white powdery mycelium is seen. Many of the fungicides used to manage these two very different diseases are fairly specific to either one, so be sure to have an accurate diagnosis.
Late blight has been confirmed on tomatoes in Wayne and Ashland counties this week. We also found downy mildew in basil, cucumber and melons in our sentinel plots in Fremont and Celeryville, OH. Downy mildew is assumed to be widespread on cucumbers and melons in Ohio, but we have not yet found downy mildew on squash or pumpkins. The late blight and downy mildew pathogens are related and all are favored by moderate temperatures, rain, high humidity and cloudy skies. Tomatoes, potatoes, cucurbits and basil should be scouted regularly and treated with protectant fungicides. Management recommendations have been posted this summer for all of these diseases. See the following:
Cucumber downy mildew was confirmed in Delaware and Franklin counties this week. Cucumber and melon growers in northern and central Ohio should assume that downy mildew risk is high and should protect their plants with fungicides. Since downy mildew has also been reported on cantaloupe and cucumber in Kentucky (Lexington area), it is likely that theses crops are also at risk in southern Ohio. A list of recommended fungicides was posted here on June 28. Additional information can be found in the Midwest Vegetable Production Guide for Commercial Growers.
We still have not confirmed downy mildew on squash or pumpkins in Ohio, but we continue to monitor our sentinel plots, field research plots and commercial fields. We will be happy to check out a pumpkin or squash sample, or any cucurbit sample, for downy mildew – please send affected leaves in a box by priority mail or 1- or 2-day courier, or drop them off at out lab: Vegetable Pathology Lab, OSU-OARDC, 1680 Madison Ave., Wooster, OH 44691; ph. 330-263-3838.