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Know the Difference Between Waterhemp and Palmer Amaranth

December 1, 2017

PPO-resistant waterhemp and Palmer amaranth are 2 of the biggest challenges corn and soybean growers face during the growing season. But when looking at these weeds, some would think they’re identical twins.

Joe Wuerffel, research and development scientist at Syngenta, provides insight on how to tell the difference between them:

  • Waterhemp is primarily a Northern weed, while Palmer amaranth dominates the South.
  • Petiole length is key. Waterhemp has shorter petioles, the portion that connects the leaf to the main stem, while Palmer amaranth petioles are generally longer.
  • When looking down at the plant, Palmer amaranth leaves tend to fill out and cover the ground more so than waterhemp.
  • Waterhemp does not intercept as much light as Palmer amaranth, therefore, doesn’t grow as aggressively.
  • The flowers on waterhemp are best measured in inches, while the Palmer amaranth flowers and seed head are best measured in feet.
  • Unlike waterhemp, the female seed head on a Palmer amaranth plant is rough and has spikes that hurt to the touch.
  • At times, Palmer amaranth develops a watermark on its leaves.

This agronomic image shows the weed Palmer amarath.    This agronomic image shows the weed waterhemp.

Palmer amaranth is on the left, waterhemp is on the right.

The best way to prevent pressure from both weed species is to implement an effective weed management strategy that includes pre- and post-emergence herbicides with multiple modes of action. Acuron® corn herbicide has 4 active ingredients and 3 effective modes of action (Groups 5, 15 and 27). Its atrazine-free counterpart, Acuron Flexi corn herbicide, has 3 active ingredients and 2 effective modes of action (Groups 15 and 27). Both contain the active ingredient bicyclopyrone, which complements the other active ingredients to deliver more effective, more consistent weed control than competitive products. For optimal control, these brands should be applied before each weed emerges. Acuron and Acuron Flexi can be applied alone or pre-emergence followed by a post-emergence application of Halex® GT corn herbicide (Groups 9, 15 and 27) plus AAtrex® corn herbicide (Group 5).

Syngenta also offers an effective soybean weed control program that starts with pre-emergence, long-last residual control from BroadAxe® XC (Groups 14 and 15) or Boundary® 6.5 EC (Groups 5 and 15) herbicide. In addition, a post-emergence application of Flexstar® GT 3.5 delivers two different modes of action (Groups 9 and 14) to control resistant broadleaf weeds.

Visit ResistanceFighter.com to learn more about weed resistance management in corn, soybeans and wheat.

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