This year, nearly 500,000 acres in Nebraska were planted with dicamba-tolerant soybeans to apply some form of dicamba herbicide formulation, including XtendiMax from Monsanto, Engenia from BASF and FeXapan from DuPont. As of July 19, however, roughly 25,000 acres of soybeans have been affected by dicamba injury in Nebraska — almost all of it due to volatilization. And that number has probably climbed to about 50,000 by mid-August, said Bob Klein, University of Nebraska Extension cropping systems specialist.
At a recent Soybean Management Field Day sponsored by Nebraska Extension and the Nebraska Soybean Checkoff, Klein noted there's the good, the bad and the ugly when it comes to using dicamba on soybeans. However, there's a good, bad and ugly on just about everything, he says. "For example, if we buy a boat, the good is you've got a new boat to go fishing. The bad may come if we buy a really expensive boat and hurt the family's finances. The ugly could come if someone wrecks the boat and gets hurt," says Klein.
In the case of herbicide injury, the bad comes from injury that's mostly cosmetic and doesn't result in a yield train wreck. The ugly comes when severe injury ruins a crop.
"On corn acres, we've sprayed quite a bit of dicamba in DiFlexx, DiFlexx Duo and Status, and those are lower rates, but normally go on corn a little earlier," says Klein. "There are some fallow acres, and there were some pretty high temperatures when those were being sprayed. All of those could or did contribute to the problem. However, I'm sure a lot of it was dicamba being sprayed in soybeans."
DICAMBA INJURY IN NEBRASKA: This map shows the 343 complaints of dicamba injury in Nebraska this year, covering an estimated 50,000 acres — mostly in the eastern part of the state. This information was compiled by Amit Jhala, Extension weed management specialist at UNL, with input from Extension specialists and educators around the state.
Conventional soybeans may show cosmetic signs of injury but may not have a significant yield impact. University of Nebraska-Lincoln integrated weed management professor Stevan Knezevic recently tested injury levels in conventional soybeans, applying dicamba at V2 at 1/500 of the normal rate — equivalent to about a fifth of a teaspoon. Those soybeans saw 41% injury, but still yielded 68 bushels per acre compared to 75 bushels per acre on soybeans that had no injury. Beans sprayed later at the R2 stage saw only 13% injury, and yielded 73 bushels per acre, compared to 70 bushels on beans that weren't sprayed.
Many of the fields in Nebraska that suffered injury symptoms were consistently injured across the entire field, indicating injury due to volatility, meaning the herbicide is converted into a gaseous form due to high temperatures and carried into nearby fields. And Amit Jhala, Nebraska Extension weed management specialist notes, when it comes to volatility, "the herbicide could travel as far as a few miles."
The majority of volatilization can occur within 36 hours after dicamba is applied, but the role of temperature and other weather parameters to create temperature inversion are not well understood.
Jhala is in the process of working with UNL's High Plains Regional Climate Center to gather climate data on what some of the parameters may have been that resulted in dicamba injury this year.
"Some of the fields are now recovering, especially those that have plenty of rainfall or irrigation," Jhala says. "In some of the fields, it looks like it will mostly be cosmetic, because the plants were reproducing pods and seeds. It's hard to tell if a certain field will have X amount of yield reduction."
While particle drift wasn't the primary cause for injury this year, it's still crucial to take steps to minimize chances of particle drift, Klein says. The No. 1 factor in drift is wind. And most dicamba labels require producers to apply at wind speeds from 3 to 10 miles per hour. That's why Klein recommends that growers who are spraying dicamba use a wind meter for smartphone. The device connects with Android and iPhone devices, and can be used to record wind speed and direction and time at the boom height the operator is applying at.
Nozzle selection is another factor. Dicamba formulation labels require growers use a large particle size, and there are a few nozzles that meet this requirement. The label requires them to use the pressure that's on the label and the nozzle that's on the label.
However, when using a larger particle size, especially at a faster ground speed, it may be a good idea to use a higher carrier rate to improve coverage, Klein adds.
Of course, the benefits dicamba offers for controlling resilient weeds like Palmer amaranth can't be overlooked. Growers and industry representatives in the delta region, for example, have reported the best control of Palmer amaranth they've had in 10 years with dicamba. "We want to get rid of the bad, but keep the good," Klein says. "We hope with some really good management and application stewardship that we can manage resistant weeds problems."
If you have a complaint of dicamba injury or are willing to share any information regarding dicamba applications, including temperatures or date of application, you can share by email at firstname.lastname@example.org.