First ask yourself if you need to control the volunteer canola in your crop. Research by Dr. Rob Gulden and graduate student Paul Gregoire at the University of Manitoba (U of M) showed that volunteer canola had little impact on soybean yield when there are less than:
- 3 plants/m2 in solid seeded or narrow row soybean, or
- 1.5 plants/m2 in wide row soybean.
Although economic thresholds (ET) such as these don’t consider seed return, this is generally not a concern for canola given it’s prevalence in our crop rotations.
If your volunteer canola populations exceed the ET, the U of M researchers also assessed the effectiveness of various post-emergent herbicides (Table 1). †Control of volunteer canola by the herbicides listed in table 1 are based on comparisons of treated research plots. It’s unlikely that any of these options will provide full control of bolting or flowering volunteer canola.
Table 1: Ranking and application timing of volunteer canola herbicides in soybean
*Will not control CLEARFIELD canola volunteers
**Registered in the Red River Valley only
Another consideration: use of these herbicides on larger volunteer canola may only set plants back, resulting in later flowering canola that may cause issues during soybean harvest.
Previous research by Dr. Gulden has shown that one of the best ways to manage volunteer canola is by limiting weed seedbank additions from canola harvest losses. Slower combine speeds while harvesting this year’s canola is a good way to reduce volunteer canola populations in future soybean stands.
Submitted by Dr. Jeanette Gaultier, Weed Specialist, Manitoba Agriculture