Jun 22, 2007
Downy Mildew Confirmed in Northeast Ohio Field, New Recommendations Made for Michigan Growers

On June 20, downy mildew was confirmed in an unsprayed cucumber field located in Medina County, Ohio, according to Michigan State University Plant Pathologist Mary Hausbeck. Medina County is in northeast Ohio south of Cleveland.

This location would likely be within the trajectory of the infected greenhouse cucumbers located in southwestern Ontario. Other cucumber fields within the Medina area are reported free of downy mildew at this time.

The cucumber parcels within this region tend to be smaller in acreage and are being grown for the fresh market, she said. While Michigan is coming off of a particularly hot and dry period, the growing regions of Medina and Wayne counties in Ohio have had adequate moisture that would have provided favorable weather for downy mildew development.

The most recent forecast for movement of downy mildew sporangia from the Ontario greenhouses does include a weekly moderate risk to cucumbers in southern Michigan for Friday, June 22. Beyond Friday, the risk of downy mildew moving into Michigan from the Ontario greenhouse region is reduced to a low risk through Monday, June 25. We continue to pick up low levels of downy mildew spores in regions of the state that have a complete one-week’s worth of spore trapping. The spore counts will be updated continuously on this website as we complete the tapes.

Cucumber growers in southeastern Michigan should spray downy mildew fungicides. Previously, I recommended that cucumber growers in southeast Michigan (Monroe, Lenawee, Wayne, Washtenaw counties) apply downy mildew fungicides (See Table 1 in the attachment for recommended products). Growers in this region of the state are at the highest risk for downy mildew development and fungicide sprays should be continued. In previous years, the cucumbers have been the most susceptible, but scouting should be intense for all cucurbits including cucumbers, melons, squash, gourds, etc.

Cucumber growers in the southernmost tier of Michigan should consider making their first spray for downy mildew, Hausbeck said. Given the weekly moderate risk of downy mildew to cucumbers in southern Michigan, cucumber growers in the southernmost tier of countries (Hillsdale, Branch and St. Joseph) may want to consider making a downy mildew fungicide application.

“It is difficult to know exactly which southern Michigan counties should be included in this weekly moderate risk for downy mildew,” she said. “Applying a downy mildew fungicide spray this week is a conservative approach given the weather forecast, very low sporangial counts and absence of an infected field in Michigan. The hard part is that we’ve learned that this disease is not always predictable





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