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Weed Wisdom Nov. 2017

By Dr. Charles Geddes
photos and writing

Farming Smarter wants to express our appreciation to Dr. Geddes, Weed Ecology and Management, Science and Technology Branch, Agriculture and Agri-Food Canada for coming on board as our weed expert for these monthly posts. It means a lot to us to have this kind of cooperation from the national experts to offer timely information to our readers. Thanks, Charles!

Volunteer canola 

Volunteer canola in a soybean crop.

Canola (Brassica napus L.) is the most grown oilseed crop in Canada and contributes $26.7 billion to the Canadian economy per annum.  Due to recent domestication, however, canola retains many weediness characteristics and can appear as a volunteer weed in crops grown subsequent to canola production.  Pod drop and pod shatter contribute to large seed losses during canola harvest, averaging about 4,300 seeds m-2 or 6% of canola yield.   These seeds enter the soil seedbank, where environmental conditions such as dryness, darkness, and warm temperatures contribute to the induction of secondary seed dormancy.  Secondary seed dormancy in canola is related to seedbank persistence; which tends to last about three to four years. 

Currently, three separate herbicide-resistance systems are available for canola production.  These systems include resistance to the herbicide active ingredients glyphosate (group 9), glufosinate-ammonium (group 10) or  imidazolinones (group 2).  Undoubtedly, these herbicide-resistance systems contribute to an ease of weed management in canola using herbicides.  However, these systems also hamper chemical weed management of canola volunteers.  A prime example of this is management of volunteer canola in soybean [Glycine max  (L.) Merr].  Farmers in soybean growing regions experience difficulty managing volunteer canola due to similar herbicide-resistance systems in these crop species and limited other herbicide options.

Fall volunteer canola emergence following canola harvest in an early fall tandem disc plot.

 There are several weed management tools for volunteer canola in western Canada.  Promoting conditions that contribute to synchronous maturation of the canola crop (e.g., adequate fertility and plant density) and harvesting canola directly (without windrowing) can reduce canola harvest losses. 

Likewise, making fine adjustments to combine settings and reducing harvest speed also may reduce the amount of seed lost (and seedbank additions) during canola harvest.  Recent research in western Canada shows that a light soil disturbance (e.g., tine harrow), shortly after canola harvest, can promote volunteer canola seedling emergence in the fall. 

Fall emergence of volunteer canola following canola harvest in a zero tillage plot.


Due to harsh winter conditions, these seedlings generally are subject to winter kill, thereby depleting viable volunteer canola seed from the soil seedbank.  Taking these proactive measures will help reduce the density of volunteer canola seeds in the soil seedbank, making in-crop management of canola volunteers that much easier. 

Volunteer canola emerges following canola harvest in an early fall tine harrow plot.