By Blake Jackson
Missouri has become the fourth state to report waterhemp resistant to labeled rates of dicamba herbicide. University of Missouri Extension weed scientist Kevin Bradley says this development is “not surprising” but adds to concerns about shrinking control options for growers.
Bradley’s team grew resistant plants from seeds collected in a Saline County field in 2023. Fortunately, these plants remain susceptible to glufosinate and 2,4-D, at least for now. Bradley, who has spent over 20 years educating farmers about herbicide-resistant waterhemp, notes that resistance is widespread in the state.
Bradley research has documented ALS (2), glyphosate, and PPO resistance in every soybean-producing county in Missouri. More recent studies show resistance to multiple herbicide groups, including ALS (2), glyphosate, PPO (14), PSII (5), 2,4-D, and HPPD (27) across several counties.
“With herbicide resistance and rising chemical costs, the agricultural industry will need an integrated weed management (IWM) approach,” Bradley says. His team is exploring technologies such as weed electrocution devices, seed-destruction equipment on combines, and the role of cover crops.
Advances in drones and robotics are also creating new opportunities, with see-and-spray drones and autonomous robots capable of tilling, spraying, or blasting weeds. “Much of this is already occurring in vegetable and specialty crops,” he adds.
Bradley warns that reliance on a single herbicide until it fails is unsustainable. “Growers cannot continue to expect the next new herbicide to control waterhemp for years into the future,” he says. Waterhemp’s ability to adapt has already resulted in resistance to atrazine, ALS-, PPO-, and glyphosate-inhibiting herbicides, among others.
Bradley has been sounding the alarm since the early 2000s, noting in 2010 that “herbicide-resistant weed populations are evolving rapidly as a natural response to selection pressure imposed by modern agricultural management activities.” By 2023, he called glyphosate the “silver bullet that wasn’t,” reflecting its declining effectiveness despite continued widespread use.
Categories: Missouri, Education, General