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Something old, something new with herbicides

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.”

More good news. Companies are developing new formulations of 2,4-D and dicamba that minimize off-target movement. And they're conducting educational programs about how to slice off-target movement potential.

Older herbicides wrapped around new formulations and traits bring new weed-management opportunities and concerns.

On the next three pages, you'll find 11 questions that have popped up about this technology and answers that will tell you how to use it safely.

“They are not the ultimate solution, but another tool in your toolbox,” says Bradley.

11 Questions

And answers about new herbicide-tolerant trait and application technology


1. What is Enlist?

The Enlist Weed Control System is the herbicide-tolerant trait system that Dow AgroSciences plans to unveil in corn in 2013 and in soybeans in 2015, pending regulatory approval. The system centers on tolerance to 2,4-D and glyphosate that's contained in the system's herbicide, Enlist Duo. The system will also include tolerance to fop herbicides in corn and glufosinate in soybeans. The Enlist system features a new 2,4-D choline formulation that differs from current 2,4-D formulations. It includes Colex-D technology to address off-target concerns of 2,4-D. Dow says it slices volatility by 92% compared to other 2,4-D formulations. Studies show the new product also reduces driftable fines by up to 90% compared to conventional 2,4-D and glyphosate tankmixes. This assumes applications occur with low-drift nozzles. 

“This formulation has demonstrated an increased border of safety (from drift) and has reduced volatility,” says Dan Reynolds, a Mississippi State University weed scientist. “That's not to say drift didn't occur at all. But it was a substantial reduction in drift on what we saw in those treatments.”


2. What is Roundup Ready Xtend?

The Roundup Ready Xtend Crop System joins Monsanto's Roundup Ready 2 Yield trait with dicamba and glyphosate tolerance. It's set to debut in 2014, pending regulatory approval.

“The Roundup Ready Xtend Crop System will give control of resistant and hard-to-control broadleaf weeds,” says Rick Cole, Monsanto weed-management technical lead. “It extends application flexibility and extends the window for postemergence applications.”

Monsanto and BASF are developing separate dicamba formulations for the system that are low in volatility and drift potential. They will be market competitors.

BASF's dicamba herbicide will be called Engenia. Monsanto plans to offer two herbicide components as part of the system. Roundup Ready Xtend will be a glyphosate-dicamba premix; XtendiMax is a stand-alone dicamba formulation.

3. What is HPPD-inhibitor tolerance?

It's part of a Bayer CropScience and MS Technologies joint project to develop a molecular stack of tolerance to glyphosate and isoxaflutole (the active ingredient in Balance Flexx, a HPPD-inhibitor herbicide used in corn). The herbicide that will be used on this trait is called Balance Bean. It's expected to debut by mid-decade, pending regulatory approval. Plans are to eventually include this event – now called FG72 – in another stack with tolerance to Liberty (glufosinate).

“This gives multiple modes of action that are effective on a broad spectrum of weeds,” says Jon Fischer, traits licensing manager for Bayer CropScience. Effective multiple modes of action also act to forestall weed resistance to herbicides.

Bayer and Syngenta are also teaming up on herbicide-tolerant trait technology, conferring tolerance to the HPPD-inhibitor herbicides isoxaflutole and mesotrione (Callisto's active ingredient) with glufosinate in a molecular stack. It's set to debut near this decade's end, pending regulatory approval.

4. Why the old geezer herbicides?

It's easier and less expensive to wrap an older herbicide mode of action around a trait than to develop a new one. New formulations can also be developed to address off-target movement concerns that exist in current 2,4-D and dicamba formulations.

“Most resources from several major companies now go into seeds and genetics, not new chemistry,” says Bill Curran, Penn State University Extension weeds specialist.

Still, several companies are putting significant money into new chemistry discovery. BASF officials say it's increased its research and development investment in crop production by 23% from 2006 to 2011. That equates to more than $1 million a day.

However, discovering and commercializing a new herbicide mode of action is not easy.

“It can cost up to $250 million to find a new active ingredient,” says Nevin McDougall, BASF senior vice president.

BASF officials say some compounds for row crops have nearly made the market. However, problems like root phytoxicity would sprout up, even if the product had good efficacy on weeds.

The tide is turning, though. Several chemical companies with active discovery programs are cranking up the research, due to glyphosate-resistant weeds.

“It is definitely a target for the research community to look at finding a new mode of action all together,” says Markus Heldt, president of BASF's crop protection division. “Something novel, equivalent to a glyphosate with residual, would be a game changer.”

5. How's the weed control?

Great – unless the weed you're trying to kill resists the mode of action. That's particularly a problem with herbicide-resistant common waterhemp. “Waterhemp is really the cockroach of weeds,” says Steve Bowe, group leader of weed science and knowledge systems for BASF.

So far, this pigweed family member resists six modes of action:

  • Glycines (glyphosate)
  • Synthetic auxins (2,4-D)
  • PPO inhibitors (lactofen, as in Cobra)
  • HPPD inhibitors (tembotrione, as in Laudis)
  • Photosystem II inhibitors (atrazine)
  • ALS inhibitors (Pursuit)

In 2011, Iowa State University (ISU) weed scientists collaborated with the Iowa Soybean Association and collected 203 waterhemp populations across Iowa. Collectors submitted them due to poor weed-control and herbicide-resistance suspicions. Here are preliminary resistance levels to these herbicide modes of action from populations investigated thus far:

  • 95% for ALS inhibitors
  • 58% for atrazine
  • 54% for glyphosate
  • 6% for PPO inhibitors
  • 28% for HPPD inhibitors

Approximately 5% of waterhemp populations tested so far resist all five modes of action. Add synthetic auxin resistance exhibited by 2011 waterhemp resistance to 2,4-D in a Nebraska grass field, and you have resistance to new herbicide-trait technology before its debut.

6. So should I give up?

Not at all. It's important to note some common waterhemp that resisted HPPD-inhibitor herbicides originated in seed corn fields. In these fields, resistance resulted the way it results in every case – repeated use of the same type of control. Still, anecdotal information shows common waterhemp that resisted HPPD inhibitors also came from commercial fields, says Mike Owen, ISU Extension weed specialist.

“We just have to use what we have more wisely,” says Bill Curran, Penn State University Extension weeds specialist. “There will be the need for increased management complexity at a time when simplicity is craved.”

Here are four ideas you can do:

1. Analyze each field separately.

You don't fertilize each field the same way. “So why should you be spraying all your acres the same way?” asks ISU's Mike Owen.

Analyze each field for specific weed problems and manage accordingly, he says.

2. Use multiple modes of action.

Do you have a weed that resists glyphosate or Pursuit? Then hit it with another mode of action. Or two, or maybe three. Chances are you'll have one or more action modes that will kill it.

“Anytime you rely on a single mode of action, you run the risk of resistance,” says Damon Palmer, U.S. commercial leader for the Enlist Weed Control System at Dow AgroSciences “That is why we are so adamant on using multiple modes of action.”

It's also important that these modes of action are effective, adds Owen. If multiple modes of action are applied to weeds that already resist them (as is the case with several waterhemp biotypes in Iowa), dismal control results.

3. Include a residual preemergence herbicide.

Besides adding more action modes, better weed control and yield-potential protection often result.

Remember, moisture is still required to activate preemergence chemicals, and that always didn't happen during a droughty 2012. Odds are, though, that it will pay.

“We are losing yield by waiting too long to treat,” says Bradley. A 2011 Missouri soybean field survey shows farmers lost an average 2.4 bushels per acre by delaying postemergence herbicide applications.

Bradley adds that an overlapping residual program works especially well to control waterhemp. This program consists of first applying a preemergence residual herbicide followed by a mix of a postemergence herbicide with activity on waterhemp that's laced with another residual herbicide.

The downside is costs increase. If you have herbicide-resistant waterhemp, though, it eliminates late-season flushes and will likely boost weed control.

4. Apply on time.

Killing a 3-inch-high waterhemp plant is easier than nixing a taller plant.

“If you apply dicamba to dicamba-tolerant soybeans on foot-high waterhemp, you will not be happy,” says Bradley.


7. Will Enlist Duo move off target?

If you follow proper application procedures, Enlist Duo is designed to stay on its intended target.

Off-target movement like drift and volatility is a concern that the Save Our Crops Coalition (SOCC) has regarding 2,4-D and dicamba. SOCC is a group of specialty crop farmers and processors.

SOCC has reached an agreement with Dow AgroSciences and supports the Enlist Weed Control System. A key factor in obtaining SOCC's support was an agreement to curtail application when wind favors off-target movement toward a sensitive crop.

SOCC was also concerned that rogue applicators would spray 2,4-D amine or ester rather than the new 2,4-D choline formulation in Enlist Duo herbicide.

Those concerns have been eased.

“One key component of our discussion is a commitment by DowAgroSciences to identify applicators who use generic 2,4-D through seed and chemistry sales,” says Steve Smith, SOCC president and director of agriculture for Red Gold, an Elwood, Indiana, tomato processor. He says this move should reduce the likelihood of chemical applicators using older 2,4-D formulations prone to off-target movement. 


8. Will dicamba move off target?

BASF and Monsanto, two firms that will supply herbicides for the Roundup Ready Xtend Crop System, say no.

BASF officials say Engenia, the new BASF dicamba formulation, will have the lowest potential yet for off-target movement. Monsanto officials say the firm's Roundup Xtend and XtendiMax formulations also have low off-target potential.

SOCC isn't buying this, as it hasn't seen Engenia research or label language citing volatility potential, says SOCC's Smith (pictured). SOCC also fears dicamba formulations similar to those of Clarity will be used. That's not an acceptable formulation to cut off-target potential, says Smith.

Clarity, a DGA salt formulation of dicamba, has an excellent volatility profile and high safety level for nearby crops when stewardship guidelines are followed, counters Daniel Pepitone, BASF industry affairs manager. BASF will not sell Clarity for use in Roundup Ready Xtend soybeans. However, chemical companies will be able to sell dicamba formulations featuring DGA salts that equal those used in Clarity.

SOCC would support the Xtend system if the two firms adopted similar label language modified by Dow in its Enlist Weed Control System, says Smith. BASF's McDougall says BASF wants to engage SOCC's concerns.

So far, though, no agreement has been reached.


9. How can I reduce off-target movement potential?

Even though 2,4-D and dicamba garner much attention regarding off-target movement, all chemicals potentially may move into adjacent crops. Bob Wolf, co-owner of Wolf Consulting and Research, Mahomet, Illinois, gives these tips to help minimize off-target movement.

  • Select nozzle to increase drop size.
  • Increase flow rates for higher application volumes.
  • Use lower pressures. One exception is venturi nozzles. They need more pressure for good coverage.
  • Use lower spray (boom) heights.
  • Avoid high application speeds and rapid speed changes.
  • Avoid adverse weather conditions.
  • Avoid high winds, light and variable winds, and calm air.
  • Consider using buffer zones.
  • Consider using drift-reduction nozzles, drift-reduction additives, shields, air assist, and pulse-width modulation. 


10. How do I keep all this straight?

Weeds were easy to manage in the golden era of the Roundup Ready system. You just sprayed and they went away. Even if there was drift, chances were glyphosate would just drift over to Roundup Ready corn or soybeans.

“You will have tolerance not only to glyphosate but also to glufosinate, 2,4-D, dicamba, and HPPD inhibitors,” says Bryan Young, Southern Illinois University weed scientist.

Young draws a comparison to retired University of Illinois weed scientist Marshall McGlammary, who referred to new chemical formulations and premixes as “Can ’em and confuse ’em.”

“Now, it's ‘Bag ’em and confuse ’em' with the new seed systems,” says Young. “Let the management begin.”

Chances are higher now for accidental applications to occur, such as spraying glyphosate on a LibertyLink system.

One way to slice this potential is with a Flag the Technology system that University of Arkansas researchers promote in the state. Each herbicide-tolerant trait is matched with a different color bicycle flag. They include:

  • Red: Conventional variety with no herbicide-tolerant trait
  • White: Roundup Ready
  • Green: LibertyLink
  • Yellow: Clearfield rice technology and STS soybeans

“It's a simple approach, but it's one that helps prevent misapplications,” says Bob Scott (pictured below), University of Arkansas weed scientist. 

11. Do I have to clean out my sprayer?

Yes, especially if you spray different types of chemistry.

“If you spray 2,4-D on 2,4-D-tolerant soybeans one day and dicamba on dicamba-tolerant soybeans the next, a big issue is making sure the sprayer is properly cleaned out,” says Bradley. “That includes not only the tank, but also the hoses, booms, and other sprayer components.”

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