Weed of the Week: Palmer Amaranth

Palmer amaranth is a summer annual weed that comes out near the top of the list every year when it comes to the most problematic weeds in the US.

Palmer amaranth has a very rapid growth habit growing up to 2" a day, making timely POST herbicide applications a challenge. Herbicide resistance is also a factor to consider when facing a population of Palmer amaranth, which has been documented to have resistance to numerous herbicide modes of action. It is an outcrossing species with both male and female plants, making for a great deal of genetic diversity within populations. While long-term control may sound hopeless considering the strengths listed above, there are a few key weaknesses that can be exploited to keep Palmer populations in check.

Palmer amaranth seeds are relatively small and do not persist throughout the years in the soil seed bank, with only 5% or less remaining viable after 3 years. Palmer also germinates from within the top 1/4" to 1/2" of soil, meaning that deep tillage will move the seed below the germination zone.

Maintaining weed free fields and not letting any Palmer go to seed can greatly reduce populations and it doesn't take a lifetime to see the results of a diligent approach. In addition to cultural practices like row spacing, tillage, and hand-weeding, herbicides are one necessary step to reducing populations of Palmer. Residual herbicides like Zidua SC, Outlook, and Prowl H2O must be utilized throughout the season to provide pre-emergence control of Palmer. Residuals make timely POST applications (less than 4" weeds) with Liberty or Engenia more realistic and provide the best chance to defeat Palmer.

If you have any questions about Palmer amaranth control, please reach out to your local BASF representative.