Lack of Effective Waterhemp Control, Group 14 soil residual herbicides

The UW-Madison WiscWeeds program has been promoting diversified integrated weed management practices to alleviate the selection pressure imposed by the recurrent use of commonly adopted herbicides due to concern with the alarming rate of herbicide resistance across our agricultural landscape and as an attempt to support adoption of more sustainable crop and weed management practices.

“The WiscWeeds program recommends the use of effective soil residual herbicides for control of waterhemp populations resistant to glyphosate and other commonly used POST herbicides. But now we have documented waterhemp resistance to the very effective soil residual herbicide sulfentrazone (Group 14). That’s not good news! It’s time to truly think outside the jug and integrate chemical and non-chemical management practices.” Dr. Rodrigo Werle on behalf of the WiscWeeds Team.


  • Our results indicate that A92 is resistant to soil-applied sulfentrazone and fomesafen and, from our knowledge, this is the first documented case of waterhemp resistance to soil-applied sulfentrazone and fomesafen (Group 14 soil residual herbicides) in Wisconsin.
  • From a practical standpoint, these results suggest that the window of soil residual control of this A92 waterhemp population from southern Wisconsin with soil-applied sulfentrazone and fomesafen is expected to be reduced.
  • These results are very concerning given the importance of these two herbicides for residual waterhemp control in Wisconsin soybean production.
  • Our results highlight the importance of proactive herbicide resistance management programs, including the diversified use of effective herbicide mixtures aligned with non-chemical weed management strategies.
  • Future research will investigate the A92 response to PPO-inhibitor herbicides applied POST (e.g., Cobra, Flextar, Resource), and the molecular mechanism of resistance.

Please help us share these results with our Ag Community. Many thanks to our stakeholders that continue to support our herbicide resistance monitoring efforts. This effort is sponsored by the Wisconsin Soybean Marketing Board.

To read the full report on the WiscWeeds website, click here >>>