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Get a better handle on early weed control
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Get a better handle on early weed control

Apr 16, 2021

It’s a bit of a no-brainer that when weeds are controlled, crops perform better. But there are deeper subtleties when it comes to how and when it’s best to control weeds to maximize crop outcomes. How early is too early? How late is too late? What should be in the spray tank?

Adam Pfeffer, Agronomic Systems Manager with Bayer in St. Thomas, Ontario, says the crop itself matters when it comes to answering some of those questions.

“Corn is unique in that it determines a large portion of its yield potential early in development, around the V6 stage,” says Pfeffer. “In canola, soybeans and wheat, a greater portion of the yield potential is determined later in the growing season – often after that early weed management period.”

And while it’s true that canola and soybeans are more resilient than corn in the face of weed competition, yield loss can still be significant when weeds aren’t controlled early.

Indeed, an Agriculture and Agri-Food Canada research project looking at weed control timing in canola found that just one weed emerging before the crop had the same negative impact on yield as 100 weeds emerging three weeks after the crop.1 And research in Ontario shows that soybean yields can be reduced by as much as 80 percent when weeds are not adequately controlled during the critical weed free period.2


New traits improve early weed control options

Pfeffer says that the majority of growers already include early weed management in their field plans, but it can be easy to be lulled into complacency.

New traits like those found in Roundup Ready® 2 Technology corn, Roundup Ready 2 Xtend® soybeans, and TruFlex™ canola with Roundup Ready® Technology help by providing growers with more herbicide and timing options.

Effective weed control in corn. Bayer’s latest corn traits include Roundup Ready 2 Technology which allows growers to control weeds early with a Roundup branded herbicide from emergence to three-leaf. This provides excellent crop safety and sets up the corn crop to reach its maximum potential.

More flexibility in canola. TruFlex canola gives growers more options and flexibility when it comes to post-emergent weed control. The trait found in TruFlex canola hybrids increases the plant’s tolerance to glyphosate, and this increased tolerance allows for a much wider application window and control of a wider weed spectrum.

Pfeffer says this allows growers to spray for weeds from cotyledon right up to first flower3, giving them more time, if they need it, to get weeds under control.

And more weeds, too. The TruFlex canola system has 51 weeds on the label, including some of the tougher ones like cleavers, wild buckwheat and dandelion.

Residual weed control in soybeans. The Roundup Ready® Xtend Crop System combines the high yield potential of Roundup Ready 2 Xtend soybeans with the option of two enhanced chemistries to control difficult and resistant broadleaf weeds.

Roundup Ready 2 Xtend soybeans carry a trait that makes them tolerant to both glyphosate and dicamba. The two enhanced chemistry options that can be used with the system are Roundup Xtend® with VaporGrip® Technology – a glyphosate-dicamba premix, and XtendiMax® with VaporGrip Technology – a dicamba-only product that can be tank mixed with a Roundup-branded product.

“Our research shows a good two to three weeks of early-season residual weed control provided by dicamba in this system,” says Pfeffer, adding that this has led to an average yield gain of 2.4 bushels per acre.4

The long game

Pfeffer urges growers to think beyond the current season when it comes to early weed control. “It’s not just about maximizing your yield potential in the current growing season. It’s also about long-term sustainability,” he says. “If you don’t pay attention to weed control, land values suffer. You can hide poor fertility issues, but with weeds, it’s obvious things haven’t been taken care of.”

“To me it’s the emotional connection,” says Pfeffer. “If you have someone you care about, who you want to leave the land to, you don’t want to leave it in a mess.” 

2 results of this research are cited at:, original research paper is behind pay walls.
3 First flower is when 50% of the plants in the field have no more than one flower.
4 Source: Bayer Market Development research trials, 2008 – 2014 (n=39). Average of 2.4 bu./ac. advantage over 2-pass.