A smart start for soybeans

Drew Haines has racked up impressive corn yields in the National Corn Growers Association (NCGA) yield contest. The Middletown, Maryland, farmer applies some of the lessons used when he won the 2019 NCGA no-till, nonirrigated division with 422 bushels per acre to his farm’s soybeans, too.

“We put down a pre[emergent] herbicide on everything,” says Haines. Regardless of the crop, planting into a weed-free seedbed gets seedlings off to a good start. 

This especially pays when facing problem winter annuals. “We have been plagued with marestail,” says Haines. “It came in here three to four years ago.”

Drew Haines next to a grain bin
Photo credit: Gil Gullickson

To battle weeds like marestail, he applies a mix of dicamba (Group 4), glyphosate (Group 9), and Valor SX (Group 14) as a preemergence treatment. He follows up with a postemergence treatment of XtendiMax on soybeans. On corn, he uses a preemergence program of Balance Flexx (Group 27) and atrazine (Group 5) before coming back with glyphosate and Status (Group 4, 19). Using multiple effective herbicide sites of action also helps forestall herbicide-resistant weeds, he says.

“If you don’t put a residual preemergence down, weeds are free to grow unchecked,” says Dan Puck, an Enlist field specialist for Corteva Agriscience. “You can have a really thick population of big weeds that can be a real challenge in getting adequate postemergence control.”

Puck also stresses resistance management, even with preemergence residual herbicides. “Many good residual herbicides bring two or three different sites of action to apply to weeds,” he says. This can help forestall resistance while simultaneously nixing weed emergence.

Sometimes, though, it’s not so easy to apply preemergence herbicides. “We’ve been a postemergence state when it comes to a lot of our corn and soybeans because our spring season often is so compressed,” says Tom Hoverstad, a University of Minnesota (U of M) weed scientist. 

Tom Hoverstad
Photo credit: Gil Gullickson

That’s changing, though. “We’ve learned there are too many weeds getting by in a total post[emergence] program, and waterhemp is certainly one of them,” Hoverstad says. “We also need to use full rates of soil-active chemistry, especially when we’re dealing with Amaranthus species like waterhemp. It was obvious driving around the countryside last summer that waterhemp is our biggest problem in soybeans.”

Farmers who rotate soybeans with corn will find controlling weeds in corn will benefit soybeans in the subsequent year, says Hoverstad. 

“There’s an old adage that an ounce of prevention is worth a pound of cure,” he says. “Some of the prevention we do on Amaranthus species (like waterhemp) in the corn cycle can help us in the soybean year. Chemistry and rates that focus on waterhemp control will help out soybeans.” 

Postemergence Phase

Farmers now have several postemergence herbicide-tolerant trait platforms from which to choose. Genetics, though, should drive the seed selection choice and not the trait platform, say university agronomists and weed scientists. 

U of M weed scientists found no significant yield differences of soybean varieties in the Xtend (tolerance to glyphosate and dicamba) and Enlist E3 (tolerance to 2,4-D choline, Group 4; glyphosate; and glufosinate, Group 10) systems across three sites in 2021. 

“The main overriding factor [for variety selection] in these systems is genetic yield potential,” says Hoverstad. Through due diligence in variety selection, farmers can find varieties that yield well in either program, he adds.

Some yield differences resulted in University of Wisconsin (U of W) 2020 trials comparing soybean varieties in Xtend, Enlist E3, and LibertyLink GT27 (tolerance to Alite 27, Group 27; glyphosate; and glufosinate). However, there was no clear yield trend in varieties across all platforms on a statewide basis. 

“There are very good varieties among different platforms,” says Shawn Conley, U of W Extension agronomist. He advises farmers to research variety trials and choose top-yielding varieties for their area based on genetics. 

Mixing effective multiple herbicide sites of action also is key with postemergence herbicides used on herbicide-tolerant varieties, says Puck. 

“Going with just one herbicide site of action is a big mistake,” says Puck. In the case of Enlist E3 soybeans, the preferred tank mix partners for Enlist One (stand-alone 2,4-D choline) are Durango DMA herbicide (glyphosate) or Liberty (glufosinate). 

Not all herbicides play well together in the spray tank, though. Glyphosate and glufosinate mixed together can result in antagonism that triggers weed escapes, says Hoverstad. That’s why farmers and applicators need to check labels before mixing, he adds. 

Contact Herbicide Guidelines

Overstad was spraying weed plots on a sunny June day last year at the U of M Southern Research and Outreach Center at Waseca, Minnesota. 

“In June, our days are the longest, and we get maximum solar radiation,” he says.  

This fit especially well for one of the herbicides he applied. “I got off the tractor and thought: This is a great day to spray Liberty,” Hoverstad recalls. 

Days filled with sunshine enable contact herbicides like Liberty (glufosinate) to fully penetrate weeds. Coverage is key for all herbicide applications. 

Contact herbicides, though, can’t rely on translocation within the plant work as they do with systemic herbicides like glyphosate. Contact herbicides kill weeds by physically contacting them, which sunny days encourage.

“Liberty is not particularly strong on lambsquarters,” says Hoverstad. “If they’re hiding and we don’t get good coverage, we can miss them.”

Ammonium sulfate (AMS), a surfactant that helps increase the effectiveness of a contact herbicide, also enhances the effectiveness of a Liberty application: 10 gallons per acre is sufficient gallonage for a systemic herbicide like glyphosate, says Hoverstad. Not so with Liberty, which requires 15 to 20 gallons of water per acre. 

Early application of contact herbicides also is key. Liberty works best when applied to weeds less than 4 inches high, points out Hoverstad. 

The industry is also moving toward early postemergence applications. Syngenta’s dicamba offering, Tavium Plus Vapor Grip Technology, aims at small weeds when applied up to the V4 growth stage of soybeans as stated on its label. 

BASF is also shifting focus to earlier applications with a planned 2021 launch of Engenia Prime (Engenia, Group 4; Zidua, Group 15; and Pursuit, Group 2), pending regulatory approval. 

“This new product will emphasize the importance of early timing, when weeds are only 2 or 3 or 4 inches tall,” says Scott Kay, BASF vice president of U.S. crop protection.

Read more about

Tip of the Day

Agronomy Tip: Use Cultural Practices to Manage Weeds

Soybeans in a straight row. Tillage and crop rotation may be useful tools in weed management.

Crop Talk