Burn off early weeds to protect canola yield

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Light rates of 2-4,D or MCPA are not recommended to control volunteer canola or other hard-to-control winter annuals prior to canola since this is not a registered use and may result in herbicide injury to the crop.

First it was warm. Then it got wet. These are ideal conditions for rapid and heavy weed emergence. Growers need to control weeds early, ideally with a pre-seed burn-off, to protect their canola yield potential.

“Weeds that emerge a week before the canola crop can cause up to 50 per cent yield loss unless they’re controlled,” says Tiffany Martinka, Canola Council of Canada agronomy specialist. “Many fields are in that situation this year.”

If weeds are actively growing and frost is not forecast, pre-seed burnoff is a good strategy. “Average yield increases of 15 per cent have been observed when comparing a preseed burnoff treatment to no burnoff treatment in direct seeding situations,” Martinka says.

Glyphosate and CleanStart are the only pre-seed burn-off products registered for use ahead of canola. CleanStart includes glyphosate and carfentrazone, which will control all types of volunteer canola if used at the proper stage (one-to three-leaf). Light rates of 2-4,D or MCPA are not recommended to control volunteer canola or other hard-to-control winter annuals prior to canola since this is not a registered use and may result in herbicide injury to the crop.

Waiting for wild oats

“If you’re waiting for wild oats to emerge before spraying their preseed application, which many farmers do, take note that winter annuals could be at more advanced stages this year,” Martinka says. “Increasing the rate of pre-seed burnoff product may be required if winter annuals are close to the bolting stage. Check your crop protection guide or product label for more details on adjusting rates for specific weeds and growth stages.”

Growers seeding without a preseed burn-off will want to manage weeds with either a post-seed/pre-emergent burn-off or an early in-crop herbicide application. With post-seed/pre-emergent applications of glyphosate, be aware of the risk of injury to an emerging canola crop. With some herbicide-tolerant systems, the application will have to occur before the crop emerges. That means a tight application window given the crop will also emerge quickly with warm soils and good moisture.

Whichever method growers choose, the key is to control weeds early in the season. Young canola seedlings are not very competitive. Weeds emerging before or with the crop take up moisture and nutrients and choke out the crop, leaving a thinner stand.

Keep your canola field as clean as economically possible until canopy closure to minimize stress and maximize genetic yield potential. After canopy closure, the crop is much more competitive. Any weeds emerging after that stage will have limited effect on yield.

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