Volunteer canola is a significant weed across the Prairies, and given the difficulties with the 2019 harvest, it will likely be a larger issue in the spring of 2020, says Ian Epp, Canola Council of Canada (CCC) agronomy specialist for northwest Saskatchewan. “Fields with overwintering canola or canola that came off late in harvest will likely have dropped more seed. I would prioritize volunteer canola management in these fields.”
Volunteer canola is a host for flea beetles and diseases like blackleg and clubroot, and volunteers from a clubroot-resistant variety “may not have the same level of resistance as the canola you bought (the parent plants),” says Epp. “It’s probably likely that they won’t.”
In addition, volunteers have not had seed treatments, so they can also introduce seedling diseases into your crop, according to CCC’s Canola Encyclopedia.
The first step in controlling volunteer canola, says Epp, is to add an effective tank mix partner to glyphosate for the pre-burn application. He adds, “Early in-crop herbicide applications are more effective at protecting yield, so spray early.” See 2020 provincial crop protection guides for specific herbicides.
In addition, CCC reports the vast majority of canola seed is destroyed by the elements during the first two years, so it’s best to grow two or even three crops between each canola crop to greatly reduce the volunteer population. Epp advises farmers, if they have flexibility with their rotation, to pick a crop this year that has good in-crop herbicide options for those fields with particularly high volunteer canola populations. Cereals are a good choice as they provide a broad range of pre-seed and in-crop herbicide options for any type of canola volunteer.
Other integrated weed management tools that will make a crop more competitive, says Epp, include increasing the seeding rate, narrower row spacing, banding fertilizer and avoidance of spring tillage to allow for maximum volunteer emergence before planting.
Canola Encyclopedia also recommends farmers leave canola seeds on the soil surface after harvest: “Delay fall tillage, if using, until a few weeks after harvest. That gives time for seeds to germinate in the fall (most of which will die through the winter) and for birds and insects to eat seeds. Also, dormancy of canola seed does tend to be reduced if canola remains near the soil surface.” Seeds of Brassica napus varieties that are incorporated into the soil develop induced secondary dormancy and can persist for up to four years in the soil.
Controlling herbicide-tolerant volunteers
CCC reports “volunteers can have single herbicide-tolerant traits, but with outcrossing, more volunteers also have stacked traits — Roundup Ready, Liberty and/or Clearfield traits.” To control volunteers with either single or stacked herbicide tolerance, spray plants at the two- to four-leaf stage. Stacked volunteers, even if they happen to have all three traits, are still susceptible to common herbicides, states the CCC, including 2,4-D, MCPA, bromoxynil and various other products. Basagran, a Group 6 herbicide, can control all canola volunteers in peas, flax, beans and other broadleaf crops.
In addition, if some volunteers germinate on a field planned for canola, the CCC reports CleanStart, Aim, Contour and bromoxynil are registered for pre-seed application before canola, providing tank mixes for straight glyphosate.
According to CCC, products available for use ahead of wheat and barley include the following:
- 2,4-D (must be mixed with glyphosate)
- BlackHawk (Aim + 2,4-D)
- Bromoxynil (must be mixed with glyphosate)
- Dicamba (must be mixed with glyphosate)
- Express Pro (tribenuron methyl and metsulfuron methyl) (must be mixed with glyphosate)
- Heat (must be mixed with glyphosate)
- Inferno Duo (must be mixed with glyphosate)
- Priority (florasulam)
- Tribenuron (must be mixed with glyphosate)