With the possible loss of the herbicide Enlist Duo, Arkansas soybean growers may find their already thin weed-fighting arsenal whittled down to one option: crop rotation.
Making the best use of that option is going to be a major topic in this winter’s production meetings, said Tom Barber, extension weed scientist for the University of Arkansas System Division of Agriculture.
Last month, the Environmental Protection Agency asked a federal appeals court to revoke the registration of Enlist Duo about a year after the agency approved its use in half a dozen states, including Arkansas. The Arkansas State Plant Board approved the use of the Enlist Duo weed control system, which combines glyphosate – commonly known as Roundup — and 2,4-D choline, in December 2014.
The herbicide was never implemented in Arkansas, however, as growers waited to hear whether China would accept beans grown with the herbicide, said Jason Norsworthy, professor of Crop, Soil and Environmental Science for the Division of Agriculture.
“This year was really going to be more of a ‘seed increase year’ in the field, and an opportunity for some growers to get familiar with the technology,” Norsworthy said. “I don’t think that in the first year of launching this technology, we were going to see it on a sizeable amount of acres, but we definitely could have seen it on acres on which we need it.”
Jeremy Ross, extension soybean agronomist for the Division of Agriculture, said that although no one could say how close U.S. growers were to achieving “China approval” on beans grown with Enlist Duo, the process took about five years when Bayer CropScience applied for trade approval from China for LibertyLink soybeans.
While pigweed isn’t a new foe for Arkansas cotton farmers, the increasing presence of PPO-resistant strains of the weed have placed a greater burden on growers attempting to maintain yields. PPO herbicides are some of the most widely used pre- and post-emergence weed control options in the region.
As of Dec. 2, crop and weed specialists with the Division of Agriculture had confirmed PPO-resistant pigweed in soybean fields in at least 12 counties.
Norsworthy said that growers in Arkansas with PPO-resistant pigweed currently have no effective modes of action available against pigweed in Roundup Ready soybeans, and many may now choose to plant LibertyLink.
“LibertyLink is the only opportunity to have a post-emergence control option,” Norsworthy said. “The Enlist technology was going to provide them another control option, and we really like to see two effective modes of action from a post-emergence standpoint.“
According to an EPA statement issued last week, the agency is seeking to deregister Enlist Duo because it has received new information from Dow that “suggests two active ingredients could result in greater toxicity to non-target plants.”
Barber said that “growers will have no available options for postemergence control of PPO-resistant Palmer pigweed in conventional or Roundup Ready systems, therefore rotating to a Liberty Link system is highly recommended.”
In fields with PPO-resistant weed problems, producers should “plan on rotating these fields to corn, milo or rice, where multiple herbicide options for pigweed control are available,” he said.
“If soybeans are planted back into these fields next season, herbicides or premixes that contain Dual (metolachlor), metribuzin or Zidua should be considered in a pre-emerge application.”