Soybean School: Is doubling up against herbicide resistance worth the risk?


For OMAFRA weed specialist Mike Cowbrough there are three fundamentals when it comes to weed control in soybeans.

The first thing growers need to remember is weeds that emerge before and with the crop have the greatest yield impact. Number two on his list is the need to keep the crop weed-free up to the 3rd trifoliate. Finally, when it comes to IP soybeans, growers should avoid higher rates of products or doubling up similar modes of action, which can lead to crop injury.

But when it comes to managing glyphosate-resistant Canada fleabane in IP soybeans, is doubling up on modes of action worth the risk? Cowbrough tackles this question in the latest episode of RealAgriculture Soybean School.

We catch up with Cowbrough at the Elora Research Station as he compares different weed control strategies, including tank mixing Eragon and Authority – two Group 14 herbicides.

“If I had Canada fleabane and I wanted to put down a soil-applied herbicide I would want to mix those two together,” says Cowbrough. But do you risk injuring the crop? “What we’ve experienced in these trials over the past three years is when you mix something like Eragon with another Group 14 herbicide … we do initially see a bit more crop injury – we need to prepare ourselves for that,” he says.

Growers will see some leaf distortion on the lower leaves, says Cowbrough “but through the passage of time we haven’t yet seen any yield reduction. He advises growers to consult with their agronomist and herbicide representative to get local input before employing the strategy.

It all comes down to evaluating risk versus reward, he adds. ” I can guarantee you the risk of not controlling glyphosate-resistant Canada fleabane, prior to soybeans coming up, is going to have much greater impact on yield than the potential for crop injury when mixing these two herbicides to address that problem.”

Click here for more Soybean School episodes.


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Soybean School (view all)Season 6 (2017) Episode 7

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