Residuals Could Help Reduce Uncertainty in 2022
There are many unknowns as farmers plan for their 2022 cotton crops. One thing that is certain, however, is the need to prepare to apply and, preferably, overlap residual herbicides so growers don’t have to rely on postemergence products to carry the entire load against Palmer amaranth.
“My biggest takeaway for next year is shifting our burndown, especially in cotton, to earlier than normal, using Gramoxone instead of glyphosate and pairing it with a residual,” said Dr. Tom Barber, Professor and Extension Weed Scientist with the University of Arkansas System Division of Agriculture.
“I don’t think we’re going to have the glyphosate and glufosinate we need,” he said. “Nobody knows, but what I’m trying to do is move glyphosate out of the burndown window into our crop window.”
That would free up more glyphosate to help with weed problems other than pigweed, which developed resistance to the herbicide years ago.
“Everybody talks about pigweed being resistant, and why is glyphosate important anymore?” he said. “But it still provides a lot of nonselective activity on problem weeds, and it helps when we put other products with it.”
Once planting begins, the story on residuals is the same that it’s been. “Two residuals are better than one on the front end,” said Barber. “In cotton, I like Brake paired with something. It can be Cotoran, diuron, Warrant or an approved dicamba formulation such as Engenia or XtendiMax.
“But we need Brake in that at-planting window because we don’t have any documented resistance to that mode of action. It broadens our herbicide program. And, if it’s a wet spring, we get a long residual activity. But we have to pair it with something because if we don’t get the extra moisture needed for activation, we need another residual in the short term. That’s why dicamba, Cotoran, or Warrant can fit with that product.”
In some areas, farmers are back to where they were in 2013 and 2014 before the Enlist and Xtend cotton varieties became available, said Dr. Larry Steckel, Extension Weed Specialist with the University of Tennessee.
“That would be overlaying residuals, and that will be the key going forward,” said Steckel, who has documented resistance to the new formulations of dicamba and 2,4-D in areas of west Tennessee. “That’s starting with a residual like Valor at the burndown. With the pre-emergence herbicides, Brake would be ideal. Another would be Cotoran/Caporal.
“Then, it would be overlaying another one at early post. A lot of folks will use Warrant or Dual.”
One of the bright spots in his research last year was an application of fertilizer impregnated with pyroxasulfone or Zidua when cotton reached the sixth-leaf stage.
“A good number of farmers tried it, and it worked well,” said Steckel. “That gives you a fourth-level residual kind of layby. We didn’t see any cotton injury with it because it’s on the ground, and pyroxasulfone doesn’t need much moisture to get activated. Plus, you’re not tying up a sprayer.”
Some growers in Mississippi moved away from residual herbicides after the introduction of the Enlist and Xtend systems, said Dr. Jason Bond, Extension/Research Weed Scientist with Mississippi State University.
“We think they may need to reconsider because of supply and cost issues for glyphosate and glufosinate,” he said. “Brake and Cotoran are definitely an option along with Caparol, Direx, or Warrant for pigweed. Palmer amaranth is what’s driving the train in cotton.
“Valor has been a mainstay for years, and we’re seeing increased interest in Zidua for post-directed sprays in cotton,” he noted. “Those products may become even more important after we see the new labels for the Enlist and Xtend herbicides.”
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