Editor's note: This is the first in a series of stories about in-season dicamba use. Check back on Thursday for Part 2, a discussion of off-target movement, violations and litigation. 

“Do you know what happens when you say ‘low volatility’ five times very fast?” asks Aaron Hager, a University of Illinois weed scientist.

“All of a sudden, you start to think ‘no volatility’ — and that is not correct.”

Hager speaks cautiously about the new approval for in-season dicamba use on Roundup Ready 2 Xtend soybeans. “These formulations still have volatility issues. I don’t have any doubt they are better relative to older formulations, but low volatility does not mean no volatility,” he says.

So is the in-season dicamba approval for Xtend soybeans a green light — or a caution flag?

Bob Wolf, owner of Wolf Consulting & Research and former application technology specialist at Kansas State University, wants farmers and applicators to consider several factors now, not when sprayers are ready to roll. 

First, what are the options? BASF offers Engenia herbicide, a retooled dicamba formulation that the company says contains a less volatile salt. XtendiMax by Monsanto and Fexapan by DuPont are formulated with Monsanto’s Vapor Grip Technology, which reduces — but does not eliminate — dicamba’s well-known volatility.

That’s a distinction that matters, say weed scientists.

Hager wasn’t able to evaluate volatility with the new dicamba formulations. “We never evaluated whether or not these formulations are, in fact, lower-volatility formulations,” he notes. “We have no data to demonstrate if, in fact, it’s lower volatility.”

VaporGrip Technology performance data used for label approvals is provided by the manufacturers.

Jeff Bunting, Growmark’s crop protection division manager, says the tankmixes and adjuvants being added to the label haven’t been broadly tested in fields. “You can draw some parallels to what you see in the field and take it back to the lab, and vice versa,” explains Bunting, who spent time in laboratories while conducting his doctoral work at U of I. “But what happens when you get into a 40- or 80-acre field is completely different with all the environmental influences that come into it.”

Barring in-field research by third parties, such as universities, Bunting says the industry is putting faith in the approval process. 

“We’re going off a lot of confidence in our regulatory procedures, the EPA and the manufacturers, because they’ve done the testing,” Bunting explains. “You have to rely on the manufacturers and their research on what to expect, and then follow the label.”

Hager adds that people shouldn’t make the mistake of calling the new formulations “safer.”

“I don’t know where this notion of safety comes from,” Hager says. “This is one of the most damaging herbicides to soybeans and other dicots that we’ve ever had.”

Particle drift and vapor drift
Off-target dicamba movement can occur four different ways: volatilization, temperature inversion, cross-contamination and particle drift — the most significant challenge. Experts agree that particle drift and vapor drift are two different things.

Neither VaporGrip Technology nor Engenia’s formulation reduces particle drift. “Spray particle drift and vapor drift are two completely different entities,” Wolf explains. “I don’t care what kind of magic the companies have put into the molecule to reduce vapor drift, it still has potential for particle drift."

Particle drift was responsible for 60% of the 200 herbicide complaints in the Missouri bootheel region last year, says Kevin Bradley, University of Missouri, Columbia.

“Off-target applications — that’s what will get us in trouble,” says Jean Payne, president of the Illinois Fertilizer and Chemical Association, as she encourages applicators and farmers to start planning for label requirements.

Where dicamba works
Doug Wilson, who farms near Gridley, gives two reasons for purchasing enough Roundup Ready 2 Xtend soybean seed for one 40-acre field this year: potentially higher yields, based on trial results, and rotating systems and chemistries to combat herbicide-resistant weeds.

“It seems like we need to add a few more things to Roundup each year, so I thought adding new technology would be a good thing,” he explains.

In-season dicamba at the right rate gives farmers another tool to combat weeds that glyphosate is weak on, such as annual morningglories and horseweed, says Hager. Dicamba does not consistently control pigweed species, Hager notes, including waterhemp.

“We’ve only known that for 50 years; that should not be new news to anybody,” he says, adding that dicamba offers “good” or “very good” control of waterhemp that is 4 inches tall or smaller.

Hager says a strong preemergence residual program may buy farmers more time for successful in-season applications and reduce early-season weed competition.

Wilson plans to see how things go this season while being proactive and evaluating new technologies.

SMALL TARGET: In-season dicamba at the right rate gives farmers another tool to combat weeds that glyphosate is weak on, such as annual morningglories and horseweed, says Aaron Hager. He adds that dicamba offers “good” or “very good” control of waterhemp (pictured) that is 4-inches tall or smaller. (Photo: Bill Johnson, Purdue Extension)

Jacksonville farmer Rodney Becker agrees that rotating systems and chemistries is helping him keep herbicide-resistant weeds off his farm. Becker is rotating out of three years of LibertyLink soybeans and plans to use RR2 Xtend soybeans on 100% of his soybean acres in 2017. Prairieland FS will apply the in-season dicamba “if the conditions are right according to the label requirements,” he adds.

Becker has already shared his plans with one neighbor and will connect with two more who will likely plant corn in neighboring fields. “We’re entering an era where there are multiple chemicals and multiple systems,” he notes. “Everyone will need to have more communication.”

Incorporating new herbicide-tolerant systems and rotating chemistries may seem like the right approach to combat herbicide-resistant weeds, but Hager and the weed scientist community stress the importance of a program strategy with multiple sites of action in every application. Hager advises against using dicamba alone as a rescue.

Learn the labels

There are three websites that all farmers and applicators should study before working with new dicamba formulations this season, says Jean Payne, president of the Illinois Fertilizer and Chemical Association.

• engeniatankmix.com
• xtendimaxapplicationrequirements.com
• fexapanapplicationrequirements.dupont.com

Ryan Rector, Monsanto’s technology development manager, explains that approved nozzles, tankmix partners and adjuvants will change right up to the day of application.

Engenia herbicide contains a new salt that lowers volatility, says Chad Asmus, BASF technical marketing manager. He recommends the On Target Application Academy training module for an in-depth application tutorial.

Application label requirement highlights:

• Adjuvants. Do not add ammonium sulfate (AMS) or acidifying water conditioners.

• Wind speed minimum. Do not apply Fexapan or XtendiMax when wind speeds are 3 mph or less due to inversion risk. For Engenia, applicators must verify inversion risk per label requirements.

• Optimum wind speed window. Apply when wind speeds are between 3 and 10 mph.

• Identifying sensitive areas. These areas include, but are not limited to, vineyards, nurseries and vegetable crops. Payne recommends using FieldWatch.com as a starting point, but don’t forget to ask neighboring landowners about non-GMO crops, seed production acres, LibertyLink crops or other non-dicamba-tolerant crops and sensitive areas. Trees, pastures and Conservation Reserve Program ground are considered sensitive areas.

• Downwind buffer the day of application. The buffer should be 110 feet wide for a 0.5-pound acid-equivalent-per-acre application for the three new dicamba formulations, or 220 feet wide for a 1-pound acid-equivalent per acre for XtendiMax and Fexapan.  

• Boom height.  The sprayer boom should be 24 inches above the target pest or crop.

• Spray volume. The spray volume should be 10 gallons per acre.

• Equipment ground speed. Run up to 15 mph, while maintaining spray volume and pressure.

How are retailers dealing with these requirements? Are you looking for a tool to help determine the right application conditions? Watch for Part 3 of this series, “How the ag industry will deal with dicamba,” on Friday.

MANAGING VS. CONTROLLING WEEDS: Aaron Hager, University of Illinois, recommends targeting 4-inch weeds with all herbicides, not only the new dicamba formations. “This goes back to when people were actually managing weeds instead of simply trying to control them, and I think there’s a big difference between those two phrases,” he says.

What is VaporGrip Technology?

Get ready for a chemistry lesson.

VaporGrip Technology comes down to pH, hydrogen ions and dicamba salt, says Ryan Rector, technology development manager at Monsanto. “We’ve come to understand through research and confirmed with academic partners that when dicamba is in the tank, along with other products that reduce the overall pH of the solution, hydrogen ions are being added to that solution,” Rector says.

Hydrogen may combine with dicamba salt, turning it into an acid form. “The acid form of dicamba is the most volatile form,” Rector explains.

He adds that new XtendiMax with VaporGrip Technology prevents hydrogen ions from combining with dicamba salt, keeping it from turning into the more volatile acidic form.

“XtendiMax is a step change in dicamba formulations as far as reducing the volatility potential with dicamba,” says Rector. “It’s not the silver bullet.”

That’s why AMS and other acidifying adjuvants will not be on the XtendiMax label. “It goes back to the hydrogen ions and the overall pH of that solution,” Rector notes.

AMS and other acidic adjuvants would turn the retooled dicamba formulation back into a more volatile form.