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Weed resistance spawns new soybean herbicides

Agriculture.com Staff 07/14/2010 @ 11:00pm

A decade ago, glyphosate was well on its way to becoming the only game in town in the soybean herbicide market. The nonselective herbicide obliterated nearly all weeds while sparing Roundup Ready soybeans. Any glyphosate-resistant weeds were just a gleam in a weed's genome.


That's changed. Today, glyphosate resistance has been confirmed among 10 species in 23 states. Other weeds are requiring higher rates of glyphosate for effective control. Continual use of glyphosate has also shifted weed populations in some areas.


"My observation driving around the state (Iowa) last summer is that we have a boatload of fields becoming increasingly weedy despite the best efforts that we have," says Mike Owen, Iowa State University Extension weed specialist.


It's the same case for other states. "The consistency of glyphosate is not as good as it used to be," adds Aaron Hager, University of Illinois Extension weed specialist.


"My prediction is that glyphosate will be driven to redundancy in large parts of North America and South America," says Stephen Powles, professor and director of the Western Australia Herbicide Resistance Initiative at the University of Western Australia.


Particularly disconcerting are the weeds resistant to multiple modes of action. In Illinois, a quad stack of a common waterhemp biotype has been confirmed with resistance to the following action modes:

  • Triazines (atrazine)
  • ALS inhibitors (imazethapyr, active ingredient in Pursuit)
  • PPO inhibitors (lactofen, the active ingredient in Cobra)
  • Glycines (glyphosate)

But, chin up. Sure, resistance to glyphosate and other modes of action exists. Still, glyphosate will remain a cornerstone of row-crop weed control, says Owen.

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