The ideal time to control weeds is a shifting target, but an agronomist with the Canola Council of Canada says that by following several key principles, growers can ensure they are getting the maximum benefits from their weed control efforts.
“The number one principle is to concentrate on controlling early emerging weeds, at the one- to four-leaf crop stage, and worry less about the later emerging weeds, at the four- to six-leaf crop stage,” said Christine Mardell.
“Spraying later-emerging weeds is for esthetics.”
According to work that the Alberta Research Council has done on wild oats, 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. Therefore, producers should try to control weeds when canola is at the one- to four-leaf stage to maximize profitability.
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For good early-season weed control, produces should consider using a pre-seed burn-off treatment such as glyphosate. Canola council trials found significantly higher yields with a pre-seed burn-off compared to no burn-off.
For optimum weed control, wait as long as possible to apply the burn-off because it will maximize weed seed germination.
However, do not wait beyond the ideal seeding date, Mardell said.
In general, producers should watch the growth stage of weeds rather than weed numbers because early weeds will cause the greatest yield reduction.
“This illustrates another key principle of good weed control – field scouting,” Mardell said.
“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.”
If a herbicide-tolerant canola will be grown, producers can wait until more weeds emerge and apply an in-crop herbicide.
They have the option of one in-crop application or applying a sequential treatment. If relying on one application, recognize that weed competition is greatest at early crop stages. Therefore, a single application should be early enough to keep the crop weed free at its most vulnerable stage.
