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Fighting glyphosate-resistant weeds


September 18, 2019
By Sponsored by Corteva Agriscience

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The best strategy for preventing and managing herbicide resistance is to change the weed control pressure you put on weeds every year. Using a variety of herbicide, cultural and mechanical tools is key to managing the weeds in your fields.

With glyphosate-resistant weeds becoming more of a problem every year, using multiple tools is especially crucial.

“Part of being able to take advantage of market opportunities is having the ability to effectively control weeds in your crop choices. A weed control toolbox full of robust tools ensures that when weed challenges – like glyphosate-resistant weeds – appear in your crop, they can be dealt with effectively to minimize impacts on yield and quality,” says Jeff Loessin, the category leader for corn, soybean, cereal, and forage seed with Corteva Agriscience in Canada.

Herbicide tools
“The number one strategy for managing glyphosate-resistant weeds is to use effective herbicides from other modes of action,” he says.

“Using all the herbicide tools in your toolbox is also very helpful,” he adds, noting that includes practices like rotating herbicide groups, using herbicide products with multiple modes of action, and choosing crop varieties with stacked herbicide-tolerance traits. Such practices help not only in controlling glyphosate-resistant weeds, but also in reducing the risk of developing other herbicide-resistant weed populations.

A two-pass approach with several modes of action can be a good strategy. Loessin says, “Using a burndown herbicide prior to planting and then having effective in-crop herbicide options means you can take control of difficult weeds and reduce the overall population of weeds, including those that are glyphosate resistant.”

Another good practice is weed scouting. Scouting before spraying helps you decide whether to spray and what to spray. Scouting about a week after spraying allows you to assess the herbicide’s performance and to spot any isolated, uninjured weeds that might be herbicide resistant so you can get rid of them before they go to seed.

Cultural and mechanical tools
“You also need to maintain the use of non-herbicide tools,” he notes. These include mechanical practices, like the timely use of tillage, and cultural practices, like using diverse crop rotations and growing competitive crops.

For example, a rotation with both broadleaf and cereal crops gives more choices in the herbicide modes of action that could be used. Plus, this diversity helps reduce disease and insect problems in the rotation, so you have healthier crop stands that are better able to outcompete weeds.

Other options for increasing crop competitiveness include choosing crop types and varieties that tend to emerge quickly and close their canopies quickly, and using good agronomics, like recommended fertilizer rates and seeding dates.

A new choice for soybean growers
The new Enlist weed control system, which includes Enlist E3 soybeans, is an option for growers who need to tackle glyphosate-resistant weeds and other difficult weeds in their soybean crops.

“The Enlist weed control system provides another option for weed control in corn and soybeans. Especially in soybeans, the modes of action that can be used in-crop have been limited. Enlist E3 soybeans are tolerant to glyphosate (a Group 9 herbicide), glufosinate (Group 10) and 2,4-D (Group 4). Enlist Duo, which contains glyphosate and 2,4-D, is registered for pre-plant through to in-crop applications at the R2 stage of soybeans,” Loessin explains.

Loessin adds Enlist Duo controls more than 70 weeds, including the toughest grass and broadleaf weed species.

“The Group 4 and Group 9 modes of action in Enlist Duo give effective control of key weeds that glyphosate alone is not strong on. And for the broadleaf weeds that are resistant to glyphosate, the Group 4 activity provides control. In Eastern Canada, Enlist Duo will effectively control glyphosate-resistant Canada fleabane, giant ragweed, common ragweed, and waterhemp. In Western Canada, Enlist Duo has activity on volunteer canola and glyphosate-resistant kochia, as well as many other problem weeds, like dandelion and wild buckwheat.”

Further, the formulation of Enlist Duo with Colex-D technology provides further advantages.

“It provides built-in drift reduction that limits the off-target movement via physical drift. When a sprayer is fitted with air induction nozzles, the physical drift can be reduced by 90 per cent, versus a sprayer applying glyphosate and 2,4-D ester through flat fan nozzles. As well, the Enlist Duo formulation has a significantly reduced potential for volatility or vapour drift. This means Enlist Duo will stay where it’s applied.”

Loessin adds, “Because of the advantages that the Colex-D technology delivers for control of both types of drift, only products containing Colex-D technology are recommended and registered for use on Enlist crops. Today, the only product that meets these criteria in Canada is Enlist Duo herbicide. The use of products containing a different form of 2,4-D, MCPA or any other phenoxy herbicide is not recommended or registered.”

As always, be sure to follow the label instructions when applying any herbicide.

A program approach
Stewardship of herbicide modes of action is vital for sustaining the performance of herbicide-tolerant cropping systems and avoiding resistance issues that can develop with overreliance on a single mode of action. A program approach, using all the tools in the toolbox, is essential.

For growers in Eastern Canada who choose Enlist E3 soybeans, this means applying a soil residual or burndown product with a mode of action in addition to Groups 9 and 4, followed by a post-emergence application of Enlist Duo. If a second post application of Enlist Duo is needed, it must be made at least 12 days after the first application, per the product label.

For western Canadian producers, the recommended program for Enlist E3 soybeans is to apply a soil residual or burndown product with a mode of action in addition to Groups 9 and 4 when glyphosate is used in-crop in two out of four years. A post-emergence application of Enlist Duo is recommended, and if a second post application of Enlist Duo is needed, it must be applied at least 12 days after the first.

As well, both these Enlist E3 programs can include in-crop glufosinate, a Group 10 herbicide with no known weed resistance in Canada. So, for example, growers could apply a burndown of Enlist Duo with a residual and then clean up any missies with glufosinate in-crop.

According to Loessin, these program approaches offer many benefits. “They eliminate yield-robbing early competition from a wide spectrum of early-season grass and broadleaf weeds. They include multiple modes of action for resistance management. They enable timely post-emergent applications for optimum weed control and reduced weed competition when the crop is most vulnerable. And Enlist Duo has a wide window for application to Enlist E3 soybeans.”

For 2020, Enlist E3 soybeans are available across most maturity groups used in Canada, and the choices of varieties will expand in the coming years. Growers interested in Enlist E3 and Enlist Duo can talk to their seed and crop protection retailers about best use practices for trait stewardship and the herbicide.