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2018 Could Be Do or Die for Dicamba

The year 2017 was supposed to be the year the Roundup Ready 2 Xtend System for soybeans got it all together. Finally, farmers planting dicamba-tolerant soybeans could choose from three accompanying dicamba formulations that manufacturers marketed as low in volatility to minimize off-target movement. 

The verdict? Well, dicamba enabled farmers to control weeds that resisted several herbicide modes of action. 

“Dicamba has never been a strong pigweed herbicide, so we wondered how effective it would be on waterhemp,” says Bob Hartzler, Iowa State University (ISU) Extension weed specialist. “We were all impressed with how well it performed.” 

Then There’s This

Adding several shades of gray to the dicamba-tolerant system are problems that resulted when dicamba didn’t stay home. Off-target dicamba resulted in 2,708 dicamba-related injury cases that state departments of agriculture investigated. Meanwhile, an analysis by the University of Missouri (MU) showed dicamba injured 3.6 million acres out of 89.5 million soybean acres planted nationwide in 2017. 

tom-wahl
Tom Wahl
Off-target damage also damaged fruits, vegetables, and trees. Tom Wahl, a chestnut tree grower from Wapello, Iowa, had previously experienced slight off-target herbicide damage. Damage was nothing like 2017, though. 

“I saw a lot of damage on leaves,” he says. “Leaf margins were tightly curled, and I had never seen that before.

“I am not a radically antichemical person,” adds Wahl. “I used to be a certified pesticide applicator and still use herbicides.” However, he says synthetic auxin herbicides (like dicamba) have the propensity to drift long distances and damage off-target plants, even when used according to the label.

Appears to Be Moving Miles 

Federal regulators approved dicamba-tolerant soybeans for the 2016 season. However, they didn’t approve matching dicamba formulations advertised as having low volatility to minimize off-target movement. Rogue applicators applied older and illegal dicamba formulations that moved into and injured non-Xtend soybeans and vegetable crops. 

Matters were expected to change in 2017. The Environmental Protection Agency (EPA) approved the following herbicides for use in the system. 

  • BASF’s Engenia
  • DowDuPont’s FeXapan Plus VaporGrip Technology
  • Monsanto’s XtendiMax with VaporGrip Technology 

kevin-bradley
Kevin Bradley
Despite being advertised as low in volatility, the worm started turning last June. One day, Kevin Bradley stopped at the intersection of U.S. Route 60 and Missouri Route 25 near Dexter in southeastern Missouri. 

“I looked off to my left and noticed one volunteer soybean plant,” says the MU Extension weed specialist. 

Intrigued, Bradley got out of his car to inspect it. The plant exhibited the classic cupping of dicamba damage. Since the closest soybean field was ¾ mile away, the dicamba had to have traveled at least that far to move off-target. 

This single soybean plant exhibited the soup that many farmers experienced regarding off-target dicamba damage.

“Dicamba appeared to be moving miles,” says Bradley. 

This scene was repeated in 25 out of 34 states in which dicamba was applied on dicamba-tolerant soybeans. That’s prompted some states to enact dicamba restrictions more strict than federal ones. The Arkansas Plant Board has enacted an agricultural-use dicamba ban from April 16 to October 31 in that state, although Monsanto is contesting this move in court. 

Dicamba Differs When Applied to Soybeans 

Corn farmers have successfully used dicamba for decades, says ISU’s Hartzler. Use on corn differed, though, in that applicators historically applied dicamba prior to adjacent soybean emergence or in the early vegetative stages. If off-target movement occurred, early-growing soybeans were much less susceptible to yield-impacting damage, says Hartzler.

That wasn’t the case last year. Dicamba soybean applications could be made when neighboring non-dicamba-tolerant soybeans were well into vegetative stage development. Damage is more likely to impact nondicamba-tolerant soybean yields in later growth stages than early ones, says Hartzler. 

An analysis by Andrew Kniss, a University of Wyoming weed scientist, suggests nondicamba-tolerant soybeans exposed at rates as low as 1/4000 of recommended use rates could cause a 2.5% yield loss at the R1 (beginning bloom) to R2 (full bloom) stages.

Last summer, Monsanto contacted customers through commercial chains to assess if any off-target damage occurred.  Through these contacts, 1,222 applicators supplied data for review and evaluation. In 91% of those cases, applicators had self-reported errors from one or more label requirements that could have contributed to off-target movement. These include factors like:

  • Insufficient buffers
  • Wrong nozzle type
  • Boom height set too high
  • Improper tank mixes
  • Wrong spray pressure

“This is not a criticism of applicators,” says Scott Partridge, Monsanto vice president of global strategy. “This label has a fair amount of structure for a reason. When the product is applied according to the label, this modern technology will control difficult-to-control weeds. It also will stay home.”

Then There’s Volatility

Hartzler says these factors contributed to off-target movement. “It is the volatility we cannot manage,” he says.

Volatility results when a herbicide converts to a gas. When this happens, the herbicide in a gaseous form can leave the application site and damage plants where it lands. 

A 2017 MU trial evaluated soybean plant injury for volatility following application of Engenia, XtendiMax, and the older, more volatile Banvel formulation. MU scientists took air samples and placed indicator plants at six time intervals following dicamba formulation applications ranging from 0 to 2 hours to 24 to 72 hours out. MU scientists recorded visual injury symptoms 21 days following application. 

The injury gap between Banvel and the XtendiMax and Engenia formulations marketed as low in volatility weren’t as much as Hartzler expected.  

In the 24- to 72-hour window, for example, 22% of plants treated with Banvel showed visual injury 21 days after application. Soybeans with injury from XtendiMax, though, weren’t far behind with 18% injury. Engenia had the lowest rate of injury at 11%. 

“There was just a 20% (damage) reduction with XtendiMax compared with Banvel,” says Hartzler. “I say that is not enough.” 

Findings like these are what prompted Hartzler and Mike Owen, a fellow ISU Extension weed scientist, not to recommend postemergence dicamba applications in 2018 in Iowa. 

Although EPA label additions enacted late last year will help curb particle drift and spray tank contamination, they do not address volatilization, says Owen. “They summarily ignored the volatilization issue that we believe exists with dicamba products,” he says.

robb-fraley
Robb Fraley
Manufacturers disagree. “We’ve done exhaustive testing on XtendiMax formulations,” says Robb Fraley, Monsanto chief technology officer.  He says Monsanto tests show that XtendiMax herbicide has 100 times less volatility when compared with older generic dicamba products. 

It may be tempting to halt potential damage from off-target dicamba by planting dicamba-tolerant soybeans this year. Still, that shouldn’t form the basis of a farmer’s soybean variety selection strategy, says Shawn Conley, University of Wisconsin Extension agronomist.

“Pick varieties on performance and not technology alone,” he says. 

What to Do? 

Dicamba remains under the watchful eye of states and the EPA. Registration of dicamba use in dicamba-tolerant soybeans will expire on November 9, 2018.

EPA documents show registration will automatically expire “. . . unless the EPA determines before that date that off-site incidents are not occurring at unacceptable frequencies or levels.” 

Translation: Use of dicamba in dicamba-tolerant soybeans depends on those who use it.

That makes following the label critical, says Gary Schmitz, BASF Midwest technical service regional manager. 

“For applicators unwilling or unable to follow application requirements specified on the label, we recommend that they not use Engenia herbicide,” says Schmitz. “Dicamba is just one tool out of many available for managing weeds. It doesn’t need to be applied on every acre.”

Dicamba label changes 

What if companies marketing products for dicamba-tolerant soybean technology threw a party and no one came?

Last October, the EPA added new 2018 label changes. “My contention is that, due to the label changes, it is nearly impossible for applicators to use the product legally,” says Bob Hartzler, Iowa State University Extension weed specialist.  

EPA Rules

Key changes compiled by Aaron Hager, University of Illinois Extension weed specialist, include the following.  

  1. Restricted-use product classification of XtendiMax, Engenia, and FeXapan herbicides. Only certified applicators can purchase or apply them.
  2. Dicamba or auxin-specific training for applicators. 
  3. Dicamba application record keeping.  
  4. Wind application windows between 3 to 10 mph wind at a boom height of 24 inches above the soybean canopy. The wind window is down from 15 mph in 2017. 
  5. Sunrise-to-sunset applications to dodge temperature inversions.  
  6. Extensive sprayer cleanout procedures.
  7. Enhanced susceptible crop language. An example is, “Do not apply this product when the wind is blowing toward adjacent nondicamba-tolerant susceptible crops.” 
  8. No applications within 24 hours of rain.

Hartzler bases his application skepticism about the new restrictions on points like the boom height above the canopy. “What commercial sprayer can keep it less than 24 inches above the canopy?” he asks.

Complications also exist within the 3- to 10-mph wind speed window. A dicamba review by Extension weed specialists including Hager; Mark Loux, Ohio State University; and Purdue’s Bill Johnson and Joe Ikley remind applicators that wind gusts in 2017 exceeded last year’s 15 mph ceiling. They recommend no applications occur above 10 mph winds, even if sustained wind speeds are below that level.

Monsanto officials say increased education will help applicators comply with new label rules. They predict Xtend soybean acreage doubling from 2017 to 50 million acres out of an estimated 90 million soybean acres in 2018. 

“The (application) errors we did find are easily addressable through the enhanced education we continue to do,” says Scott Partridge, Monsanto vice president of global strategy. 

Even so, many university weed scientists fear education and training won’t be enough. “We hear from the captains at Monsanto that we can easily fix this (off-target dicamba movement) with increased training,” says Larry Steckel, University of Tennessee Extension weed specialist. “I don’t think we can. I will do my best, but I think we are fighting a losing battle.”

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