New Year, Same Cotton Weed Message: Start Clean, Stay Clean
January 29, 2021 When the Ninth Circuit Court of Appeals vacated the original labels for newer, over-the-top dicamba herbicides in June 2020, a nearly audible gasp was likely heard in cotton fields from coast to coast about losing an important tool mid-season (followed by a sigh of relief when EPA allowed use of current stocks).
The subsequent re-registration of XtendiMax, Engenia and Tavium herbicides in October 2020 helped relieve some of the anxiety in planning weed management programs for 2021. In a December episode of Cotton Grower magazine’s Cotton Companion podcast, three Extension weed specialists – Stanley Culpepper of Georgia, Tom Barber of Arkansas, and Peter Dotray of Texas – discussed the new label and what it means for growers this season.
“The focus this time was really on how to reduce volatility,” said Culpepper. “EPA asked us a lot of good questions about our research and our data. But one of the challenges with this technology is that the data in Georgia is not necessarily the same as it is in Arkansas or Texas. Understanding the environmental conditions that influence a product like dicamba has been part of our growing experience.”
“I think EPA looking at the data and working with the companies and realizing that some things needed to be changed on the label was important,” noted Barber. “The label recognizes the importance of pH buffers and keeping the pH up at a level where it reduces volatility. We’ve known for a few years that adding glyphosate to the tank reduces the pH and increases the volatility.”
Increased buffer zones and new cut-off dates for dicamba use in cotton and soybeans will likely require more attention and discussion between the states and EPA. Arkansas will maintain its current May 25 cut-off date across most of the state, and, as Dotray pointed out, those restrictions may or may not be an issue in all parts of Texas.
“We’ve had a few conferences already with the Texas Department of Agriculture,” he said.
Getting Started in 2021
More work and information about the dicamba label will be coming as planting approaches. But as much as things continue to change, some things – like tried and true herbicide programs – stay the same.
Culpepper – “Nothing’s changed for the program for next year. You have to start clean. Some growers prefer tillage – I prefer a cover crop – with the herbicides up front. Put two active ingredients that are effective on Palmer amaranth behind the press wheel, make a timely post one application and a timely post two application with some residuals if you need them. Then, run a layby rig or hooded sprayer where you can get some diuron or other chemistry in there. That layby application will protect that farm, not just the cotton crop.
“If we miss anything, my growers are going to pull those weeds out of the field. We don’t want to add any seed to the seed bank.
“The principals of the plan – diversified, integrated – have not changed and will not change. We’ll try to address some of these new significant dicamba restrictions the best that we can. Cooperation is the key to success.”
Barber – “Where we fall behind is up front, especially making that first post application. One thing that I’ve seen with Arkansas’ dicamba cut-off date is that growers seem to want to get as many pigweed up as possible before they hit it with dicamba. We lose a lot if we miss that first application. And that’s where we get behind, whether it’s dicamba, glufosinate or Enlist. That first timely post is the most critical for setting the rest of the season up. If we lose the battle in a particular field, that’s usually where we lost it.”
Dotray – “The short answer is there is nothing new, just continuing the importance of starting clean and using at-plant herbicides so we only have small weeds at the first post application. It’s not cutting corners in economic times when the temptation to do so is certainly there. It’s the full rate and the appropriate carrier volume. And it’s making sure at the end of the year that all weeds are not producing seed.
“We’re doing a lot better at understanding the biology of Palmer amaranth. Some recent research shows, at least in Texas, that the viability of the seed is very short, which I think is encouraging to suggest to growers that, in a short amount of time, we can bring some of these weed seed levels in the soil down to a much more manageable level. The key is to remain diversified, start strong and finish strong.”
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