Waterhemp is already one of the most problematic weeds in the Midwest and South. But researchers writing in the latest edition of the journal Weed Science say its control challenges are getting even tougher.  Waterhemp is developing a significant level of resistance to multiple herbicides, including the auxin herbicides now used as an alternative to glyphosate.

A team from the University of Nebraska-Lincoln recently planted seeds collected from a single population of waterhemp that survived treatment with the auxin 2,4-D.  They found their new waterhemp “crop” to be at least 30-fold more resistant to 2,4-D than waterhemp populations susceptible to the herbicide. The plants also were three-times more resistant to the auxin herbicides aminopyralid and picloram, and they were resistant to two additional classes of herbicide with different modes of action, the ALS and PSII inhibitors.

What does all this mean for weed control? The authors of the article say it’s time to mix things up. Growers must use a diverse combination of cultural tactics and herbicide mixtures to control waterhemp and keep it from going to seed.

If you’d like to know more, read the article “Multiple-Herbicide Resistance in a 2,4-D-Resistant Waterhemp (Amaranthus tuberculatus) Population from Nebraska” in Weed Science Vol. 65, Issue 6, November 2017.