While it may seem like a challenge to control volunteer glyphosate-tolerant (GT) canola, good pre-season planning that includes pre-seed herbicide tank mixes supported by solid crop rotations and effective harvest management can greatly improve your ability to manage the issue.
The best opportunity to include a tank-mix in your herbicide program is pre-seed. Tank-mixing at least once per growing season helps control volunteer canola and reduces your risk of developing herbicide-resistant weeds.
“If you know you’re likely to have glyphosate-tolerant volunteers, take care of them during pre-seed burn-off,” says Jamie Mills, canola product line manager with Nutrien Ag Solutions, adding that glyphosate alone is not enough. “By adding a different mode of action as a tank-mix, those volunteers are easily controlled.”
A common misconception is that reducing glyphosate use overall will decrease the risk of herbicide resistance. In many cases, herbicides considered high risk for developing resistance, such as groups 1 and 2, are substituted in place of glyphosate but this puts growers at a greater risk of developing resistant weeds. Managing resistance isn’t about using less glyphosate – it’s about using herbicides more effectively.
Tank-mixing glyphosate with another mode of action can vastly reduce the selection pressure on resistant weed populations and provides greater residual control. By including an effective residual herbicide in your pre-seed tank-mix, you can keep your fields clean longer, control later flushes of canola volunteers and reduce the selection pressure for resistance to post-emergence herbicides.
“We also need to break our reliance on herbicides with high resistance risk,” says Mills. “Rotating crops that all use the same single-modes of action puts heavy selection pressure on the weed population and eventually could result in those weeds developing herbicide resistance.”
The best time to manage GT volunteer canola actually begins at harvest, says Mills. Building an integrated weed management plan includes reducing the amount of loss out of the back of the combine.
“Timing is everything,” says Mills. “Swathing an even maturing crop at the right time, properly setting the combine, along with good hybrid selection are important factors in minimizing the spread of seeds.”
Researchers with the University of Manitoba studied canola harvest losses on farms across Western Canada from 2010 to 2012. The study found that harvest losses averaged roughly six per cent. Not only does that represent lost revenue, but also contributes to the volunteer canola seedbank.
The study also showed that the management decisions made by growers are one of the highest contributing factors to those losses, with some producers able to consistently achieve lower harvest losses than others through improved management.
A yield loss of even one bushel an acre can put 1200 seeds per square metre back on the ground. Those seeds can volunteer the next year and create pre-seed and in-crop weed pressure on the next crop in your rotation.
Diversifying your crop rotation is also an effective strategy to help manage disease, insects and weeds – including volunteer canola – according to Mills.
“A well-planned crop rotation makes good agronomic sense. Having a four-year strategy will make life easier,” says Mills. “Then you can use glyphosate, the best weed control option in your canola because there are so many more options to control volunteer canola in subsequent years. In a strong rotation it becomes a non-issue.”
Having two to three years between Genuity® Roundup Ready® canola crops provides an opportunity to vary your herbicide program and can help manage weeds through differing levels of competition. Mills says the year after your canola crop is typically the easiest time to control GT volunteers and is most easily done through tank-mixing.