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Something old, something new with herbicides

Gil Gullickson 12/05/2012 @ 9:55am Crops Technology Editor for Successful Farming magazine/Agriculture.com

Sometimes, old fashions make a comeback: World War II leather bomber jackets, 1950s-style crew cuts, patent leather purses, knee-high boots.

Then again, there's a reason why some old things stay closeted: bell-bottom jeans, fanny packs, lime-green leisure suits.

Hit-and-miss old fashions mimic the opportunity and concerns regarding the new herbicide-trait technology that's coming down the pike in the next few years.

“Soybean varieties with tolerance to 2,4-D, dicamba, and HPPD inhibitors (such as Balance Bean, a new herbicide product) are new options being offered by several companies as new tools for managing glyphosate-resistant weeds,” says Kevin Bradley, University of Missouri Extension weeds specialist.

Current formulations of these herbicides blitz soybeans. No longer. Several companies have developed traits that tolerate these herbicides. That's good news.

In some Missouri regions, common waterhemp currently resists several herbicide modes of action, Bradley says. In these cases, Liberty (the herbicide used in the LibertyLink system) is the only viable postemergence herbicide that controls waterhemp. In time, continuous use of Liberty will also result in waterhemp resisting that herbicide or herbicides with that mode of action, too.

Why the comeback?

There was a reason why older chemistries stepped aside when the Roundup Ready technology first debuted in 1996. The system – first in soybeans and later in corn – initially created weed-management nirvana by killing virtually any weed. This prompted farmers to nix other herbicides in favor of repeated glyphosate applications on Roundup Ready crops. Ultimately, repeated applications spawned glyphosate-resistant weeds and spurred development of these herbicide-tolerant traits. Systems that include 2,4-D, dicamba, and HPPD inhibitors are part of a multiple herbicide mode of action strategy that controls a broad weed spectrum.

Concerns exist, though. Current formulations of synthetic growth auxin herbicides – 2,4-D and dicamba – have off-target concerns due to drift and/or volatility. This is particularly a concern for specialty crops and the vineyards that have recently cropped up in the Corn Belt. If off-target movement damages specialty crops, applicators could be responsible for damage of these crops, which can be valued up to $10,000 per acre.

Bear in mind, weed resistance has already surfaced to these chemicals. Waterhemp already resists six modes of action, including some HPPD inhibitors and synthetic auxins.

The good news is that these new technologies are tools you can use to help forestall herbicide resistance. “The big thing is not to go Callisto/Callisto/Callisto or Balance/Balance/Balance or 2,4-D/2,4-D/2,4-D all of the time,” says Bradley. “These traits are just a bigger Band-Aid if we continue to apply the same herbicides over and over. If we abuse them, their effectiveness will go down. Weeds will evolve resistance to these modes of action as well.”

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