With glyphosate-resistant Palmer pigweed foremost in most west Tennessee farmers’ minds, UT researchers continued to look at ways to best control it. Early control with residual herbicides like Cotoran, Caparol and Reflex worked best, even in the LibertyLink program, says Kelly Barnett, a UT doctoral student working at Jackson.

“A lot of 6-inch pigweed didn’t go down easy, even with one shot of gramoxone,” Barnett says.

“Our only post-emergence option is Liberty, not Roundup. I want to stress that. And it’s no good to apply Liberty to pigweed that’s too big or with the wrong nozzle or in the wrong weather conditions. The pigweed has to be 4 inches tall or less. When it’s bigger, you may get control at times, but it will be inconsistent.”

Best Palmer pigweed control comes when applying Liberty in at least 15 gallons of water per acre through flat fan nozzles, Barnett says. Application timing is critical, as well.

“Go at least two hours after sunrise. Applications near sunrise give 40 percent to 50 percent control. We’ve seen even better control by waiting until four hours after sunrise. Applications at 10 a.m. give greater than 90 percent control. Time of day will influence how Liberty is working,” she says.

Liberty is “finicky,” Barnett says. “The very narrow window to apply Liberty shows how finicky this herbicide is.”