Waterhemp image courtesy of University of Nebraska-Lincoln Cropwatch.

Chalk up another win for Waterhemp and a loss for farmers. Waterhemp resistant to Group 15 herbicides (very long chain fatty acid inhibitors) has been documented in Illinois research plots. This is the first time a broadleaf weed has shown resistance to herbicides in the Group 15 chemical family anywhere in the world.

University of Illinois weed scientist, Dr. Aaron Hagar says it’s unknown how widespread the resistance is for now. However, he urges that this development punctuates the need to take a diversified approach to weed management practices. With this new finding, waterhemp has shown resistance to seven different herbicide sites of action.

Group 15 (long-chain fatty acid inhibitors) herbicides include:

  • S-metolachlor (Dual Magnum)
  • Acetochlor (Harness, Warrant, Degree, Surpass NXT, Topnotch)
  • Pyroxasulfone (Zidua)
  • Dimethenamid-P (Outlook)

Source: University of Illinois