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Downy mildew is an aggressive disease in processing cucumbers that can appear rapidly and have a devastating impact on crops. There’s the added challenge of the pathogen’s ability to continually adapt and develop resistance to existing chemistries – reinforcing the need for ongoing testing of registered products and evaluating new options to support the Ontario processing cucumber industry.
“For more than 20 years, research has helped identify effective fungicide programs, support resistance management strategies and contribute to the registration of new fungicide products,” says Rachel Riddle, part of a research team that recently evaluated fungicides at the Ontario Crops Research Centre – Simcoe. “This research provides growers with management options to protect yield, fruit quality and the long-term viability of cucumber production.”
The fungicide efficacy trial was conducted during 2025 at the Ontario Crops Research Centre – Simcoe, led by University of Guelph’s Rene Van Acker, with research technicians Riddle and Lisa Weber.
The team evaluated 15 different treatments, including an untreated control, on the parthenocarpic variety “Springsteen” to reflect the shift to plant these hybrid varieties that don’t require pollination and produce seedless fruit.
Here are some key findings:
- Orondis Ultra is still the most effective registered product to control downy mildew to levels that don’t have an economic impact on the final crop yield, even under high disease pressure.
- Torrent and Zampro provided immediate control suggesting that if used in a program with Orondis, these products remain the best down mildew control option.
“Research on fungicide products for cucumber downy mildew control is critical to maintaining a sustainable cucumber industry in Ontario,” says Riddle.
Read the full research report Efficacy of fungicides for downy mildew control in processing cucumbers.
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