New soybean weed control tools for 2021

Soybean farmers have numerous weed management tools from which to choose in 2021.

These include old standbys like Xtend soybeans with the matching herbicide package of dicamba (Group 4) and glyphosate (Group 9). Enlist E3 soybeans, launched in 2019, tolerate 2,4-D choline (Group 4), glyphosate, and glufosinate (Group 10).

Joining these packages in 2021 is Alite 27, a new Group 27 (isoxaflutole) preplant/preemergence soybean herbicide that federal regulators approved in 2020. Farmers in labeled counties may apply Alite 27 – the first Group 27 herbicide that matches GT27 (tolerant to isoxaflutole and glyphosate) and LibertyLink GT27 (tolerant to glyphosate, glufosinate, and isoxaflutole) soybeans. 

Another new entrant for 2021 is XtendFlex. “It’s the first trait that has tolerance to dicamba, glyphosate, and glufosinate, and it’s built on the proven performance of Roundup Ready 2 Yield technology,” says Lisa Streck, Bayer Crop Science North America soybean launch lead. “We’ll have products available from Maturity Group 0 to 7. XtendFlex will be available in all our Bayer branded products as well as our Corn States licensees.”

It’s Complicated

Complexity though, accompanies these tools. 

“Weed management in soybeans is now more complicated than before because we have so many traits,” says Debalin Sarangi, a University of Minnesota Extension weed specialist. “There’s a need for more record keeping.”

Herbicide-tolerant traits also aren’t a cure-all for managing weeds. “We learned a lot from the launch of Roundup Ready [glyphosate-tolerant soybeans in 1996],” says Mike Henderson, Atticus executive vice president for Central U.S. crops. “We overrelied on a herbicide technology to control weeds.” 

Many weeds have since resisted glyphosate and now resist herbicides used in new herbicide-tolerant systems. Last July, greenhouse and replicated field trials confirmed dicamba-resistant Palmer amaranth in Tennessee, says Larry Steckel, University of Tennessee Extension weed specialist. 

So far, glufosinate applied to glufosinate-tolerant soybeans has dodged weed resistance. This may be changing, though. Tom Barber, University of Arkansas (U of A) Extension weed specialist, observed several Arkansas Palmer amaranth patches in July 2020 where it appeared control via glufosinate was not as effective as in the past. Further testing, though, is needed before resistance is confirmed, he says. 

That’s why resistance management programs are key. “Through our education programs, we highlight the importance of a strong [preemergence] residual herbicide and use of multiple modes of action for a strong program and limited amount of weed resistance,” says Bayer’s Streck. 

Herbicides are just part of the herbicide-tolerant trait equation. Seed plays an equally important part. 

Some single-trait seed offerings still exist, but the seed industry has largely moved to stacked-trait events, says David Thompson, national marketing and sales director for Stine Seed Company. “From an integrated weed management perspective, the stacked traits are a better option,” he says. 

An Integrated Approach 

Herbicide-tolerant traits are valuable tools. Still, they’re just one part of an integrated weed management plan, says Henderson. He advises farmers to first consider driver weeds in a field.

“Every farm has certain weeds that are more trouble than others,” says Henderson. Familiar weeds like waterhemp plague many soybean fields, while winter annuals like henbit and purple dead nettle may overrun other fields early in the year. 

Metrics like a soil’s organic matter content and cation exchange capacity can impact herbicide use rates and effectiveness, says Henderson. The half-life of a herbicide can impact its persistence in the soil. Soil solubility of a herbicide is also key, for it determines how much rainfall is required to distribute it in the soil profile. 

After considering these factors, key in on “starting clean” with no weeds at the start of planting, says Henderson. 

“We can’t overuse the idea of starting clean,” he says. “This gives crops a head start on competing weeds, he adds. Tools that help farmers start clean include:

Tillage. Although it can nix early-emerging weeds, tillage also has downsides that farmers must weigh, Henderson says. Using tillage on steep slopes, for examples, can spark erosion that erases any weed control advantage, he says. 

Burndown and preemergence residual herbicides. These tools help keep yield-robbing weeds from competing with young soybeans for water, light, and nutrients. They also ease pressure on later postemergence applications. 

Preemergence herbicides aren’t perfect, though. Residual herbicides generally require 0.5 to 1.0 inch of precipitation within seven to 10 days of application for optimal incorporation, says Aaron Hager, University of Illinois (U of I) Extension weed specialist.  

Soil condition, soil moisture content, residue cover, and herbicide chemical properties can also influence the optimal rainfall amount and the time window following application that rainfall must occur for maximum activity, he adds. 

Nor are preemergence herbicides immune to resistance. In 2019, U of A weed scientists confirmed a Palmer amaranth population that resists S-metolachlor (Dual Magnum, Group 15). 

Meanwhile, U of I weed scientists confirmed two waterhemp populations that resisted all Group 15 herbicides they tested in 2019. Previously, Group 15 resistance had just surfaced with weed grasses.

“It’s absolutely something that farmers should keep in mind if they notice weed escapes from those preemergence herbicide applications,” says Meaghan Anderson, Iowa State University Extension field agronomist. 

“We broke the big hammer when we broke Roundup [with continued use],” says Hager. “Now, we need more small hammers. Cultivation works. Rouging works. The approach of cover crops, if done right, can work. Everything helps in moving to more integrated systems.”

Mixing Matters

Herbicide resistance has brought out the inner chef in farmers and chemical applicators, as it’s spurred the use of multiple effective herbicide sites of action during application. Ditto for adjuvants like surfactants and drift-reducing additives. Then there are pH modifiers that the Environmental Protection Agency has ruled must accompany dicamba applications on dicamba-tolerant crops for 2021 and beyond. 

All these ingredients can set the stage for antagonism in the spray tank if correct components are not used or are not properly mixed together. 

“One way to make sure there isn’t an issue is to mix them ahead of time with a jar test,” says Meaghan Anderson, an Iowa State University Extension field agronomist. This can prevent farmers and applicators from cleaning out a
cottage cheese or taffy-like mess from an improper mix in a spray tank, she adds.

Carryover Concerns

Early planting can help soybeans harvest more sunlight, which spurs yield-churning photosynthesis.

Still, early birds need to check fields’ herbicide history. Those who jump the gun on planting may expose soybeans to more herbicide carryover than farmers who plant soybeans later. 

“Late planting in 2019 pushed a lot of herbicide applications back into June and July of that year,” says Aaron Hager, University of Illinois Extension weed specialist. This spurred carryover of persistent herbicides in 2020 because of the compressed time between 2019 applications and early April 2020 planting in some fields, says Hager. 

Early soybean planting teamed with a dry 2020 in many Midwestern areas amplify 2021 herbicide carryover concerns. “So much [herbicide] breakdown in the soil profile comes from soil microbes,” says Mike Henderson, Atticus executive vice president for Central U.S. crops. “In drier conditions, there is less microbial activity than there is under more moist soil conditions.”

Certain herbicides persist more in the soil than others. For example, farmers may plant labeled crops like corn and soybeans anytime following the application of carfentrazone (Aim) herbicide, says Hager. Conversely, 10 months must elapse between application of fomesafen (Flexstar, Group 14) and planting corn. 

The good news: Farmers and applicators can largely avoid carryover by following crop rotation restrictions on herbicide labels. “Never say never,
but usually, label language takes into account weather extremes,” says Hager.

New 2021 Soybean Herbicides

Soybean farmers will gain these new preemergence premixes and burndown herbicides this year to complement herbicides used with herbicide-tolerant systems. 

  • Authority Edge is an FMC preemergence herbicide that includes soybeans on its label. It’s a premix of pyroxasulfone (Zidua, Group 15) and sulfentrazone (Spartan, Group 14). Authority Edge has shown good control in Minnesota of waterhemp and common lambsquarters, and moderate control of velvetleaf and woolly cupgrass, says Debalin Sarangi, a University of Minnesota Extension weed specialist.
  • Antares Complete is a preemergence soybean herbicide from Helena Agri-Enterprises, LLC. It’s a premix of sulfentrazone (Spartan, Group 14), S-metolachlor (Dual Magnum, Group 15), and metribuzin (Sencor, Group 5). Its concentrated formulation enables Antares Complete to cover more acres than similar herbicides at equivalent field rates, say Helena officials. It nixes early weed competition with residual control of key broadleaf weeds and grasses, they add.  
  • Reviton is a Group 14 herbicide with a novel active ingredient called Tergeo, say Helm Agro US Inc. officials. This nonselective herbicide is designed for preplant burndown and desiccation in several crops including soybeans. Reviton gives burndown control of more than 50 broadleaf and grass weeds, company officials say.
  • Kyber is a soybean preemergence herbicide from Corteva Agriscience aimed at controlling weeds such as Palmer amaranth, tall waterhemp, and common ragweed. It’s a premix of three herbicide sites of action: pyroxasulfone (Zidua, Group 15), flumioxazin (Valor SX, Group 14) and metribuzin (Sencor, Group 5). It provides four to six weeks of residual activity, say company officials.

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