Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
With corn harvest underway, a few things to keep in mind about Palmer amaranth and Texas panicum. A combine is a very efficient tool for spreading Palmer amaranth seeds. Take measures to prevent spreading seeds within a field, and from one field to another. Late-season management of Palmer amaranth or Texas panicum to reduce or prevent seed production is not easy or convenient, but it will pay dividends in the future. In particular, where infestations are light. The key is not to simply pull or mow plants that have seeds, but to remove the seed from the field. Removing the plants prior to harvest will reduce the spread of the seed within the field and from field to field. Furthermore, Palmer amaranth plants hold onto their seeds more than most other species, so pulling up the plants will not result in the plants dropping all their seeds.
If a single Palmer amaranth plant can produce 500,000 seeds; spread over an acre that is 10 seeds per square foot. You can quickly see how eliminating seed production and preventing the spread of seed with equipment is a tremendous help.
After corn harvest, some fields with late emerging plants or light infestations may need to be mowed or sprayed with Gramoxone/paraquat for Palmer amaranth, or glyphosate for Texas panicum to prevent late-season seed production.