Mark VanGessel, Extension Weed Specialist; email@example.com
I have seen Palmer amaranth seedlings emerging in corn fields that had no preemergence herbicides applied.
There are Palmer amaranth plants in DE and MD that are resistant to glyphosate. So fields with Palmer amaranth present, or fields where you suspect it is present, need to be treated with an effective herbicide (or herbicide combination) that will provide postemergence control as well as residual control. Some considerations include atrazine, Callisto, Capreno, Impact, Permit Plus, Halex, Realm Q, Resolve Q. Other products such as Status or Liberty provide effective postemergence control, but will not provide residual control.
Palmer amaranth plants look very similar to smooth and redroot pigweed. However, Palmer amaranth leaves, stems, and petioles do not have hairs (smooth and redroot pigweed do have fine hairs). Palmer amaranth’s leaves have long petioles that are often as long, or longer, than the leaf blade. As a result, the leaves often droop. Occasionally, leaves will have a variegated “V” mark or watermark across the leaf blade. On-line photos can be found at http://extension.udel.edu/ag/files/2013/05/AMAPA_images_lg.pdf