Agronomy Centre

Gone are the good ol’ days and the simplicity of glyphosate-tolerant or conventional soybeans. Today, we have numerous platforms—what does it all mean, and why should you care? Well, the simple answer is herbicide-tolerant weeds. It began back in 2010, when the first glyphosate-tolerant Canada fleabane was found in Essex County. All of a sudden, our bulletproof weed-control system began to fall apart. As time has passed, more glyphosate-tolerant weeds have emerged in Ontario. Giant ragweed, common ragweed, and, most recently, waterhemp (multiple modes of action resistant) have come to the forefront. This brings me to the conversation of what herbicide platform should be used and where does one platform have a better fit than another. 

Currently, RR2, RR2 Xtend, XtendFlex, Liberty, and Enlist E3 trait platforms are available in Canada. In the U.S., Balance GT (Isoxaflutole [HPPD Gr. 27] and glyphosate-tolerant) soybeans are also available. Beginning this past year, there has been a large push on the Enlist E3 front. Enlist is a Corteva trait complex that combines Roundup, Liberty, and 2,4-D tolerance in soybeans. Enlist’s herbicide flexibility, its slightly lower volatility, and lower risk from temperature inversions are big selling points, especially in areas where alternative crops and vegetables are grown. E3 beans can be sprayed with Corteva’s new 2,4-D choline formulation in the form of Enlist One or Enlist Duo, which contains REL of glyphosate. 2,4-D is exceptionally strong on glyphosate-resistant giant ragweed and will edge out dicamba (Xtend) in control. 2,4-D also has a play over dicamba on field horsetail. Despite being a weed with little effect on yield, field horsetail can become an eyesore and somewhat of a hassle in some areas of your field. With Enlist soybeans, it’s also important to remember that 2,4-D is weak on Canada fleabane. However, this is easily overcome by a pre-plant application of 2,4-D plus the addition of Eragon and Merge. 

RR2 Xtend soybeans have been a mainstay for a few years now and, in some maturities, are slowly transitioning to newly approved XtendFlex soybeans, which combine Liberty tolerance with the current dicamba tolerance in Xtend soybeans. Dicamba is still a superior herbicide in control of glyphosate-resistant fleabane, with a strong edge over 2,4-D. Dicamba is actually commonly the stronger of the two Gr. 4 herbicides on most broadleaf weeds except for the key weeds mentioned above. E3 and XtendFlex beans also allow the use of the Liberty herbicide program in season. Liberty is a good option when dealing with escapes of fleabane, but don’t expect it to take down weeds greater than 10 cm in height. Liberty is an awesome non-selective herbicide when sprayed on small weeds under the right conditions—hot and sunny—and when the proper rates of AMS are added to the herbicide. Liberty can also boast that there are currently no resistant weeds in Canada to it. However, Italian ryegrass and, recently, palmer amaranth have been found to be resistant in the U.S. 

The other weed causing lots of issues is waterhemp, a notorious season-long emerging weed in the pigweed family. Keys to controlling include a residual herbicide upfront followed by an early post pass of another herbicide when it starts to escape. Dicamba and 2,4-D are both equally effective at 80–90% control on waterhemp, while Liberty lags behind at 40–50% control but has maybe more flexibility in later-season applications.

With all the new platforms and herbicide options, remember that this doesn’t mean some of the herbicide programs we have used in the past should go away. Glyphosate, Eragon, Merge, and Sencor (metribuzin @ 220g/ac) are still great options pre-plant in any type of soybeans to control Canada fleabane. Sencor is important because it greatly improves the consistency in control of Canada fleabane. Sencor can be found in many co-packs of pre-plant herbicides like Boundary LQD or Canopy Pro, which also contain other herbicide groups to aid in the control of other problem weeds. Boundary contains Dual, which is good on grasses, and Canopy Pro has Classic, a Gr. 2 herbicide with some strength on dandelion and thistles when combined with glyphosate. 

Ultimately, it will be important to use all the resources available to you. Contact your seed representative, chemical representative, or retail salesperson and identify what weeds are key problems on your farm. With their help, you can develop a solid gameplan to keep that soybean field weed free in 2022!

Readers may also be interested in this in-depth discussion of Enlist vs. Xtend from Maizex’s 2021 winter agronomy video series, “Decipher, Debate, Decide”: https://youtu.be/ebustmT43fM.