A fall-applied plant growth regulator pushed winter canola overwinter survival past 85% at New Liskeard, Ontario, compared with roughly 60% in untreated plots, in a multi-site project led by Agriculture and Agri-Food Canada (AAFC) and the University of Guelph.

The four-year programme, funded by the Ontario Canola Growers Association and the Ontario Agri-Food Innovation Alliance, runs through 2028. Researchers are testing fall-applied plant growth regulators (PGRs), three planting dates and 10 hybrids across four Ontario sites: Harrow and Woodslee in the southwest, Winchester in the east, and New Liskeard/Temiskaming Shores in the northeast.

Why focus on the growing point?

Unlike winter wheat, winter canola overwinters with its growing point above the soil surface, leaving it exposed to cold. PGRs that reduce internode elongation aim to keep that apical meristem lower in the canopy.

"Could PGRs help growers here in the southwest to manage a long fall and really robust canola growth?" asked Eric Page, a research scientist with AAFC at Harrow. "And would that be a benefit both to overwinter survival and yield in southwestern Ontario with our established growers?"

PGRs labelled for winter oilseed rape in Europe are the products in the trial. No product currently holds a Canadian registration for fall application on winter canola. Sprays go on at the six- to eight-leaf stage at three doses — a control, a 1X European label rate and 2X or 4X rates to test spray-overlap scenarios.

What do the early results show?

Across two seasons, Page's group saw no consistent PGR benefit at Harrow, where winterkill is already low. At Woodslee, moderate rates helped when planting was delayed and the crop came under stress.

Joshua Nasielski, an assistant professor at the University of Guelph who leads the Northern and Eastern Ontario Agronomy Research Group, said the northern data tell a different story. "The most promising PGR product resulted in more than 85 per cent survival compared to about 60 per cent in the control plots without PGRs."

Mercedes, the only winter canola variety currently registered in Ontario, yielded 2,318 lb/acre in 2024 and 2,099 lb/acre in 2025 at New Liskeard when planted at the optimal date and left untreated. Plot survival topped 60% in both years.

Spring canola in the Temiskaming region averaged about 2,300 lb/acre in 2024 and 2,200 lb/acre in 2025, putting the New Liskeard winter canola plot yields in the same range. Experienced southwestern Ontario growers can exceed 80 bu/acre, equivalent to 4,000 lb/acre.

Which hybrids are catching attention?

The project compares Mercedes against European-bred winter canola lines. At New Liskeard, overwintering success varied sharply by hybrid. Page said some hybrids responsive to PGRs showed a 40% increase in overwinter survival.

"For some of the winter-hardy hybrids that are responsive to the PGR, we can see yields between 40 and 50 bushels (2,000 to 2,500 pounds per acre) in New Liskeard," Page said. That range is comparable with regional spring canola yields.

Higher survival at New Liskeard did not automatically mean higher yield. "The higher winter survival with PGRs didn't translate into higher yields; the yields were similar or slightly lower with the PGRs," Nasielski noted, adding that final conclusions depend on the dataset through 2028.

What does this mean for planting dates?

The trial also probes whether a PGR can widen the planting window. Optimal planting dates defined by earlier work are:

• Southwestern Ontario: first two weeks of September
• Winchester: last week of August to first week of September
• New Liskeard: August 17, plus or minus six or seven days

"If you plant your winter canola later, can a fall-applied PGR provide some advantages for winter survival?" Nasielski asked.

Page's southwest data suggest a narrow band where management lifts yield and survival. "There's really a bit of a window there where management might be beneficial," he said.

What comes next?

The team will finish the trial and analyse the full dataset to refine planting date and hybrid guidance. If final results confirm meaningful yield and survival gains from PGRs, the researchers plan to build a dataset supporting a minor-use registration for fall-applied PGRs on winter canola in Canada.

"We can give farmers some more detailed information about things like planting dates, the usefulness of plant growth regulators, and winter canola varieties," Nasielski said.

Growers weighing the crop further north should watch for the 2028 final report and any subsequent minor-use submission to Canada's Pest Management Regulatory Agency.