While help is on the way for cotton producers battling resistant pigweed, timeliness of applications still will be the key to managing this devastating pest, according to research from this past year.

Some of the new herbicide combinations will improve flexibility to a point, but if you have good growing conditions for the prolific Palmer amaranth, they might offer only a few days, says Jeremy Kichler, an Extension agent in Colquitt County, Ga.

And very few people in the lower Southeast can speak with the experience of Kichler, who helped to confirm the first case of glyphosate-resistant Palmer amaranth in Macon County, which is known as “ground zero” for the weed in Georgia.

“Soon, cotton growers will have access to 2,4-D and dicamba technologies,” says Kichler. “Information is needed to determine the most effective mixtures for growers to control problematic weeds like glyphosate-resistant Palmer amaranth and grasses. Our field experiments evaluated possible tank-mixes of glyphosate, glufosinate, 2,4-D and/or dicamba on Palmer amaranth and Texas panicum.”

Weed resistance has been the primary issue for cotton producers in Macon County, he says. “I’ve seen growers in middle Georgia struggle with this pest for eight or nine years now. In helping my growers with this issue, I’ve seen my better growers use tactics such as managing the seed bank, using overlapping residual herbicides in their herbicide programs, and also the widespread adoption of Liberty-based programs. Practices such as this have become more common now, and we’re spending a lot of money to help keep our fields clean.”

Kichler says his growers are excited about the 2,4-D and Clarity technology that’ll be available in a few years. They see it as another tool to help manage glyphosate-resistant Palmer amaranth, he says.

But regardless of the technology, timeliness will still be a necessity, he adds. “If you look at the research on Liberty-based or auxin-based programs, we talk about the importance of timely applications to make these systems work. In our Extension-based programs for managing weed resistance, we stress to our growers about timely applications. Crop consultants are faced with daily situations where growers are trying to cover more acres, and sometimes we have issues with making timely herbicide applications, especially when we’re managing large Palmer amaranth,” says Kichler.

The objective of the field experiments this past year was to find the most effective dicamba or 2,4-D mixture for controlling annual grasses and Palmer amaranth, he says. The treatments included an untreated check, 2,4-D Amine at 24 ounces per acre, Clarity at 12 ounces per acre, Roundup at 32 ounces per acre, and Liberty at 32 ounces per acre.

Researchers also evaluated the effectiveness of various tank-mix combinations. “We used Roundup plus 2,4-D or Clarity, Liberty plus 2,4-D or Clarity, and Roundup plus Liberty plus 2,4-D or Clarity.”

There were two locations in the trial, one in Macon County and one in Tift County in southwest Georgia.