September 22, 2009 — Post harvest spraying is a great opportunity to control perennial weeds and winter annuals, according to Arvel Lawson, Canola Council of Canada (CCC) program manager of Crop Production.

“Effective control this fall will prevent these weeds from robbing fields of moisture and nutrients early next spring.”

“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,” says Lawson. “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. “Spraying this fall is a proactive way to set fields up for future years,” says Lawson.

“I recommend that farmers choose their 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. Farmers should be sure to pick a herbicide that won’t have a negative impact on next year’s crop.” Re-cropping restrictions are available in provincial crop protection guides. If targeting volunteer canola, farmers are advised to consider the herbicide tolerance of the plants.

“If farmers are considering fall tillage, they need to remember that it can be effective on small winter annuals but will have little effect on large, established perennials. Also, if farmers are working a field that was in canola in 2009, tillage should be shallow. That’s because keeping canola seeds close to the soil surface is an important part of volunteer canola management. Burying canola seeds deep in the soil can induce seed dormancy and this may ultimately result in growers having to manage volunteers arising from this year’s harvest losses for longer in rotation.”

“With the weather cooperating right now, consider a post harvest herbicide application to prepare fields for next year’s canola crop,” says Lawson.


For more information, contact:

Arvel Lawson

Program Manager Crop Production