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Hit weeds hardest in post-harvest window: CCC

Post-harvest spraying is a great opportunity to control perennial weeds and winter annuals. Effective control this fall, while the weather co-operates on much of the Prairies, will prevent these weeds from robbing fields of moisture and nutrients early next spring, according to the Canola Council of Canada.

“With high input costs, making sure nutrients are utilized by your crop, not weeds, next spring is critical,” council program manager Arvel Lawson said in a release Tuesday.

Controlling perennial weeds such as Canada thistle, dandelion, and quack grass is best done in the fall because these plants are moving nutrients down into their roots for winter. Post-harvest spraying targets these weeds at their most susceptible growth stage, which should provide better overall control than spraying at other times in the year.

Post-harvest spraying also controls late maturing annual weeds such as wild buckwheat and green foxtail. These weeds continue to set seed until there is a killing frost and spraying will help limit weed seed return.

 “We saw many weeds escape herbicide control this spring because cool spring conditions resulted in later than normal emergence. Spraying this fall is a proactive way to set fields up for future years,” said Lawson, who works out of the council’s Winnipeg office.

Choose your herbicide based on the weed spectrum in the field. In many cases, a tank mix of glyphosate with a broadleaf herbicide to “heat it up” may be your best bet. Make sure to pick a registered product that won’t have a negative impact on your crop next year. Re-cropping restrictions are available in provincial crop protection guides. If targeting volunteer canola, consider the herbicide tolerance of the plants.

After frost

Even if you have received a fall frost, there’s still time for a post-harvest herbicide application. Just make sure there is green plant material visible and wait approximately 3 days after a frost before application. If leaves have turned brown or black, wait until new green growth is visible before applying the chemical.

If considering fall tillage, remember that it can be effective on small winter annuals but will have little effect on large, established perennials.

If working a field that was in canola in 2008, keep tillage shallow as keeping canola seeds close to the soil surface is an important part of volunteer canola management. You want to avoid burying canola seed deep in the soil profile as this can induce seed dormancy. This may ultimately result in you having to manage canola volunteers arising from this year’s harvest losses for longer in rotation.

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