Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
I suspect all have heard about the need for preventing Palmer amaranth seeds from entering the soil and preventing seed production to stop the spread of seed with the combine. A few questions have come in about patches of Palmer amaranth and what options you might have late in the season.
There is no easy solution. Hand removal is the best option. Many of the plants already have seeds present so nothing short of removing the seed heads from the field will eliminate seeds from being returned to the soil. Those immature seeds on the plant will continue to pull nutrients from other parts of the plant and allow them to mature. Pulling plants and leaving them in the field, chopping plants, mowing plants, or spraying plants will not stop seed production, it will only prevent the production of additional seeds.
Palmer amaranth plants retain their seeds late into the summer and fall. Therefore, seeds will not be scattered as seedheads are removed from the field. However, that means the plants will still have seeds when the field is combined. It appears that crop desiccants will not cause seed drop either. So mature plants at the time of harvest have a very high probability of being spread, both making the current patches larger and even more troublesome, spreading seeds to other fields.
Hand removal of seedheads from the field is important, or the alternative is not harvesting these patches to prevent the spread of the seeds. If planning to mow Palmer amaranth plants on field edges, one mowing will not be enough to stop seed production. I do not know how frequent you will need to mow to stop seed production, but one mowing will not be adequate. In addition, be sure to clean the mower before you move it from an infested area, so seeds are not spread