Jun 19, 2007

Downy Mildew Reported on Cucumbers Growing in Canadian Greenhouses

Downy mildew has been confirmed on greenhouse cucumbers in Essex County in Ontario, Canada. These are not plug plants for field production but are “hothouse” cucumbers. Essex County is Canada’s southernmost county, located on a peninsula of land that juts out into the Midwest of the United States. At this time, no field outbreaks have been reported in Canada or Michigan. The greenhouse outbreak in Canada is troubling news for Michigan cucumber growers.

Field cucumber growers in Canada are better equipped to handle downy mildew than they were a year ago because of expanded fungicide labels. However, I don’t think Michigan growers can assume downy mildew will stay in Canada. The recent dry and bright sunny weather will delay downy mildew development in Canada, for now. My concern is that the downy mildew spores will leave the greenhouse and infect nearby cucumber field plantings. If cucumber fields become infected in Canada, then our risk in Michigan increases. The vegetable crop specialist in Canada recommends that Canadian field cucumber growers spray preventively.

Cucumber growers in southeastern Michigan should spray fields preventively now. If growers in areas of the Midwest closest to Essex County spray diligently, perhaps a 2007 epidemic can be averted.

Sprays can be banded for fields that are young and newly emerged. Cucumbers that have been growing under tunnels will be larger and will need to be completely covered with spray to be protected.

A spray interval of 10 days is recommended. The following fungicides are recommended: Gavel, Previcur Flex, Ranman and Tanos.

Alternate these products and mix each with either mancozeb or chlorothalonil (Bravo). This development will be watched carefully and new information and recommendations will be posted on the Web site plantpathology.msu.edu.