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Where Dicamba Stands for 2017

This promising weed-control system will be closely watched.

A couple of years ago, Mid-South farmers who had been pummeled by glyphosate-resistant Palmer amaranth raptly listened to a perky sales representative pitching a new herbicide-tolerant system. 

The rep accurately pledged that this dicamba-based system would control pesky pigweeds. What about volatility? Well, this system would feature new system formulations that would slice this dicamba drawback. 

What if an applicator applied an existing dicamba formulation on dicamba-tolerant soybeans? Not to worry. “That would be off-label and illegal,” correctly said the sales rep. 

The weed scientist who relayed this story to me noted that a grizzled old agronomist sitting in back wasn’t taking this well. 

“All it takes is one person to screw it up,” he grumbled. 

Or more. Last summer, thousands of soybean acres in Missouri, Arkansas, and Tennessee exhibited symptoms of dicamba damage. Although federal regulators in 2016 approved dicamba-tolerant soybean varieties under Monsanto’s Roundup Ready 2 Xtend soybeans, they didn’t approve dicamba formulations that match it. Complaints center around allegations that unlabeled formulations of dicamba not labeled for use on Xtend soybeans injured neighboring non-Xtend crops.

So what now? Here’s where dicamba-tolerant systems stand for 2017. 

  • At least two dicamba formulations fit Roundup Ready 2 Xtend soybeans. Federal regulators have approved Monsanto’s XtendiMax with VaporGrip Technology and BASF's Engenia, both low-volatile dicamba formulations. 
  • Dicamba controls some weeds better than others. On marestail, it improves on the traditional burndown tankmix of glyphosate and 2,4-D, says Aaron Hager, University of Illinois Extension weed specialist. 

It also gives better control on tall and ivyleaf morningglory and common and giant ragweed over glyphosate. 

Waterhemp? Most university weed-control guides list dicamba as good or very good on waterhemp, but not excellent as was glyphosate. Dicamba can improve control of pigweed species, but it will never be as effective as glyphosate once was prior to resistance, says Hager.

  • Applicators better read labels. Specifics on boom height, sprayer speed, and nozzle type and buffers exist.
  • No tankmixing is allowed. For 2017, applicators will be required to apply new dicamba formulations alone. Other herbicides must be applied separately, says Hager.
  • Little third-party yield data exists. Farmers will need to largely depend on the word of seed companies regarding yield potential. 
  • Low volatility won’t curb all off-target potential. New dicamba formulations do feature low volatility. However, no uniqueness exists about their ability to physically drift during application, says Hager. 
  • The feds are watching.

The new registration for dicamba use in dicamba-tolerant soybeans expires November 9, 2018. Hager says EPA documents indicate the registration will automatically expire “. . . unless the EPA determines before that date that off-site incidents are not occurring at unacceptable frequencies or levels.”  

The upshot? Be careful. Continued use of dicamba in dicamba-resistant soybeans hinges on those who use it. Abuse via off-target movement could cause the feds to nix it, says Hager. This tool is too valuable to fritter away. 

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