Timing weed control in canola isn’t easy, but the task can be made easier if producers keep a few important principles in mind, said Christine Mardell, the Canola Council of Canada’s agronomist in northwestern Alberta’s Peace River region.
- Use a pre-seed burn-off treatment such as glyphosate for good early season weed control.
Mardell said council trials found significantly higher yields after a pre-seed burn-off compared to no burn-off. On average, crops that had a pre-seed burn-off produced 15 percent more than crops that didn’t. Based on a crop yield of 30 bushels per acre and a selling price of $6 per bu., that’s a $27 per acre increase in profit.
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“For optimum weed control, wait as long as possible to apply the burn-off so the chemical can get to as many weeds as possible,” she said. “But be careful not to wait too long and go beyond the ideal seeding date.”
- Concentrate on controlling early emerging weeds at the one- to four-leaf crop stage and worry less about later emerging weeds.
“Later emerging weeds may be unattractive and contribute to the seed bank, but they have much less impact on yield than weeds present early in the season,” Mardell said.
She based her recommendation on wild oats research conducted by the Alberta Research Council that found weeds that emerge before or with the crop cause greater yield loss than weeds that emerge after the crop.
Fewer weeds tend to emerge after the crop has reached the four-leaf stage and those that do are usually weak and spindly.
The guidelines are different for herbicide-tolerant canola because effective weed control may still be achieved at later growth stages, Mardell said. As a result, growers have the option to wait until more weeds emerge and then apply an in-crop herbicide: either once or more often.
However, early weed control will still tend to provide higher yields and returns. If growers choose a single herbicide application, they should time it to get the weeds during early crop stages.
“Time single herbicide applications early to keep the crop weed free at its most vulnerable stage.”
- Scouting fields is important.
“Know what is growing and refer to previous weed records to get an idea of what weeds may be an issue later in the season,” Mardell said.
“The more competitive the weeds, the fewer it takes to cut yields.”
- Consider pre-seeding tillage to help control “canola-unfriendly” weeds such as cleavers, stinkweed and shepherd’s purse, or choose a herbicide-tolerant system that will provide effective control.
Mardell said these winter annuals either have no control methods in conventional canola or can require additional herbicide for effective in-crop control.
However, if erosion and adequate seedbed moisture are a concern in your area, pre-seeding tillage may not be advised.
“Light tillage in the fall can also be useful, giving 80 to 90 percent control of fall-germinated weeds,” Mardell said.
