Farmers across the Mid-South are finding it more difficult to control grasses, including goosegrass, barnyardgrass and jungle rice in their Roundup Ready 2 Xtend and Enlist herbicide-resistant crops.

Larry Steckel, professor of weed science at the University of Tennessee, discussed what he’s seeing in Tennessee at a stop on the online Milan No-Till Field Day that was recorded at a farmer’s field in Medina, Tenn.

“What we have here is Enlist cotton that we treated 13 days ago with a quart of glyphosate and a quart of Enlist One,” said Steckel, who is located at the West Tennessee AgResearch and Education Center. “After 13 days, a lot of this goosegrass, and, in fact, most of it looks like it is starting to recover and come back.

See, Day of reckoning for dicamba-2,4-D crops?

“You compare this to the treatment just ahead of it here, which is just straight glyphosate. You can see the Palmer pigweed is coming back. That’s not a surprise. We know most of our Palmer is resistant to glyphosate. But what is interesting here is that we have considerably better control of the goosegrass with straight glyphosate than with Enlist One and glyphosate.”

Steckel said researchers have seen similar occurrences in the Xtend system where dicamba and Roundup are not providing as good grass control as Roundup alone. “It looks like to control things like goosegrass we probably need to divide it up where we’re spraying glyphosate after or before but not tank-mixed with Enlist One.”

The No-Till Field Day video also included a stop at the Milan Research and Education Center where scientists are looking at grass control and with applications of the new dicamba formulations on Palmer amaranth.

“This is 12.8 ounces of Engenia that was applied three weeks ago,” he said. “You can see we have a significant number of Palmer pigweed that have recovered, are putting their face back to the sun and are looking like they’re going to be a problem for the rest of the year.

See, More than one herbicide needed for Palmer amaranth

“This the third location where we have gotten what I would consider not as good performance as we really need from a dicamba application on Palmer amaranth at the label rate of 4 inches in height.

The plot shows “we’re seeing a progression in problems, and the best way to manage it is not just figuring on one application of dicamba giving complete control,” he said. “We need it in a system where we’re using a good pre-, and we’re keeping the numbers down from the start. Then we are looking at a dicamba application followed by Liberty. Barring that, make another dicamba application or, in soybeans, a Flexstar, Cobra or Ultra Blazer.”