A study featured in the most recent issue of the journal Weed Technology shows that post-harvest treatment of glyphosate-resistant Palmer amaranth can significantly reduce seed production and help to control the spread of the weed’s resistant traits.

A research team from the University of Tennessee treated two test fields after corn crops were harvested. Fourteen days after treatment, they found that the herbicide paraquat used alone or in a mix with S-metolachlor controlled 91 percent of glyphosate-resistant Palmer amaranth in the fields.  Even better results were achieved, though, when paraquat was tank-mixed with residual herbicides to control subsequent regrowth of the weed.

Post-harvest treatments were found to prevent approximately 12 million Palmer amaranth seeds per hectare – significantly reducing the weed seedbank.

Researchers also discovered that the residual herbicides used in post-harvest treatments of Palmer amaranth had no impact on the yields achieved from a winter wheat crop subsequently planted in the same fields.

Lawrence Steckel, Ph.D., one of the authors of the Weed Technology article, says the prevalence of glyphosate-resistant Palmer amaranth has led scientists to recommend a zero tolerance policy toward the weed, with year-round management programs that incorporate multiple control methods and multiple herbicide mechanisms of action.

“We now know that herbicides applied post-harvest can play an important role in a sustainable Palmer amaranth weed management program by reducing the number of seeds left in the field by herbicide-resistant plants,” he said.  

Full text of the article, “Evaluation of POST-Harvest Herbicide Applications for Seed Prevention of Glyphosate-Resistant Palmer amaranth (Amaranthus palmeri),” is now available in Weed Technology Vol. 29, Issue 3, July-September 2015.