A recent study from the Weed Science Society of America indicates that Palmer amaranth is the most difficult weed to control in the U.S. Although Palmer amaranth has not spread to the entire Midwest, it is likely coming.

Two words come to mind when describing Palmer amaranth: aggressive and prolific. Often reaching up to 8 feet in height, this weed can grow up to 3 inches per day. In addition to its aggressive growth rate, some populations can quickly adapt to herbicides, leading to resistance. Its prolific seed production and germination throughout the season helps Palmer amaranth be more competitive than other pigweed species. Often producing tens of thousands of seeds per plant, Palmer amaranth grows quickly in open areas with full sun and undisturbed soils.

An aggressive weed like Palmer amaranth must be met with an aggressive weed control strategy for growers to achieve high yields at the season’s end. Historically, growers have waited until post-emergence when the weed has reached its full growth, and then attacked with a post-emerge herbicide. This is often unsuccessful against an aggressive weed like Palmer amaranth.

Palmer amaranth management tips:

• Start clean with a full rate of a pre-emergence herbicide like Acuron® corn herbicide or Boundary® 6.5 EC soybean herbicide
• Scout early and scout often so you can attack the weeds as early as possible
• If necessary, follow up with a post-emergence corn herbicide like Halex® GT herbicide plus atrazine or a post-emergence herbicide with fomesafen, like Flexstar GT® 3.5 for soybeans
• Maximize efficacy by spraying weeds before they exceed 3 inches

Palmer amaranth is known for its aggressiveness, but a strong weed control program equipped with herbicides containing multiple effective modes of action is the best approach to attacking this weed now and in the future.

Submitted by Dean Grossnickle, Syngenta Agronomic Service Representative

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