Farmers will need to make significant adjustments to the way they apply the Xtendimax and Enlist Duo herbicides on their dicamba- and 2,4-D-tolerant crops under the new EPA-approved labels for the products.
But one thing won’t change, according to Dan Reynolds, an Extension and research weed scientist at Mississippi State University who has been conducting studies on the drift potential for both of the herbicides for several years.
“The single most important thing we can do – well, actually, I think there’s two – and the first is to use good judgment,” said Dr. Reynolds, who spoke on his research at a meeting of the Memphis, Tenn., Agricultural Club. “If there’s any doubt, don’t pull the trigger. If there’s any doubt in your mind, don’t spray.”
The second most important thing, he said, is tip selection. “Choose one of those spray tips and the pressures that are specified on the label to try to help mitigate off-target movement.”
As Reynolds explained in an interview following his presentation at the Ag Club, the new EPA Xtendimax and Enlist Duo labels have significant changes compared to previous herbicide label requirements.
“There are restrictions on what spray tips can be used on both labels, and there are restrictions on what tank mix partners can go into those mixes,” he said. “Enlist Duo has a website; Xtend has a website, and if materials, including adjuvants, additives and drift retardant agents, are not listed on those websites, they cannot legally be tank-mixed with those herbicides at this time.
“That’s kind of unprecedented in terms of herbicides in my lifetime,” said Dr. Reynolds, who began his career as a weed scientist at the LSU AgCenter’s Northeast Research and Extension Center at St. Joseph, La., in 1984.
“This will also be the first time we will have in-field buffers specified of 110 feet for the half-pound of active ingredient of dicamba in Xtendimax and 220 feet for the 1.0-pound active ingredient of the herbicide. Again, those are safeguards to help mitigate some of the off-target issues.”
Earlier in his presentation, Dr. Reynolds talked about some of the problems that occurred when farmers were allowed to plant the dicamba-tolerant crops without a label for the herbicide formulation that was designed to be applied on them.
More than 200 complaints of off-target drift from dicamba herbicide formulations had been filed in the states of Arkansas, Mississippi, Missouri and Tennessee as of Oct. 25 in 2016.
“There were about 200,000 acres of dicamba-tolerant crops available, but no herbicides were labeled for use on those crops,” he said. “Obviously, there was a lot of illegal usage of these herbicides.”
Anticipating the potential for problems when the herbicides were registered, the Mississippi Department of Agriculture and Commerce put together a task force to come up with recommendations for the integration of the auxin herbicides into the row-crop culture.
Mandatory training program
“One of the recommendations was for mandatory training for farmers before they can apply the herbicides,” said Dr. Reynolds, who holds the Edgar E. and Winifred B. Hartwig Endowed Chair in Soybean Agronomy at Mississippi State.
Dr. Reynolds and fellow Mississippi State University Extension specialists – Jason Bond, Darren Dodds and Trent Irby – began putting together a training program to help growers use the new technology correctly.
The program consists of six training modules, according to Dr. Reynolds:
- “The first module talks about weed resistance;
- “The second talks about what auxin herbicides are, how they work in plants and the herbicide symptomology associated with those plants;
- “The third discusses off-target deposition in the form of physical drift and volatility and how these labels are trying to mitigate that with special nozzles and droplet size specifications;
- “The fourth discusses off-target deposition in the form of contaminated equipment and what do low-dose concentrations of these herbicides do; and it shows a lot of information about how much yield reductions different concentrations of these herbicides can cause and the growth stage for when that occurs;
- “A fifth will discuss the intricacies of the Enlist Duo label;
- “And the sixth will talk about the Xtendimax label.”
Reynolds, who has been studying off-target problems with herbicides for a number of years, said researchers have been surprised at how much yield loss can occur from relative small dosages of the auxin herbicides, depending on the growth stage of the plant.
“The early reproductive stages seem to be very sensitive, particularly in soybeans to dicamba and pinhead square in cotton,” he said.
Currently, only three states have training programs for the application of dicamba and 2,4-D herbicide formulations on herbicide-tolerant crops, including Georgia and Mississippi.
Reynolds said Arkansas State Plant Board officials have notified the Mississippi Department of Agriculture and Commerce they want to use the mandatory program developed by Mississippi State Extension scientists.
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