MU Weed Science Team Confirms Dicamba-resistant Waterhemp

Missouri is the fourth state to confirm the presence of waterhemp resistant to labeled rates of dicamba herbicide.

University of Missouri Extension weed scientist Kevin Bradley says this is not surprising but adds to concerns about declining control options.

Bradley’s lab on the MU campus grew the resistant plants from seeds collected from a field in Saline County in 2023. The plants did, however, remain susceptible to glufosinate and 2,4-D, for now.

Bradley has spent more than two decades educating growers about waterhemp’s growing herbicide resistance.

Bradley’s research points to ALS (2), glyphosate and PPO resistance in every soybean-producing county in Missouri. His latest research shows resistance to ALS (2), glyphosate, PPO (14), PSII (5) and 2,4-D in five counties, and ALS (2), glyphosate (9), PPO (14), PSII (5) and HPPD (27) in another five counties.

More resistance could be on its way in 2026. Three dicamba products are pending EPA approval for broadleaf weed control in 2026 following a one-year hiatus.

Bradley notes that 2,4-D resistance is increasing, and resistance to Group 15 herbicides has increased in Illinois. There is no “official” glufosinate resistance yet, but several states are investigating populations. Metabolic resistance is the predominant mechanism in the “newest” types of resistance, says Bradley.

Herbicide-resistant waterhemp is being documented farther north and east in the United States, says Bradley.