A fast-growing, highly invasive weed known as waterhemp has developed resistance to glyphosate, one of the most commonly used herbicides, posing a significant challenge for New York farmers, according to new research from Cornell University.
The study, published Jan. 13 in Weed Technology, confirms that waterhemp populations from Seneca County soybean fields are five to 12 times more resistant to glyphosate than control samples. The findings mark the first confirmed case of glyphosate-resistant waterhemp in New York, raising concerns about the future of weed management in the state.
“Having the confirmation of this resistance in New York gives us the opportunity to spread the message that we should use these chemistries more judiciously and diversify our weed control practices,” said Vipan Kumar, associate professor of weed science in the College of Agriculture and Life Sciences at Cornell.
Waterhemp, which can grow up to two inches per day and produce nearly a million seeds, was first detected in New York in 2014. Since then, it has spread rapidly across 23 counties. The weed is notorious for its ability to develop resistance to multiple herbicides, a trait that has already made it one of the most problematic species in the Midwest and South. Left unchecked, waterhemp can reduce soybean yields by 43% and corn yields by as much as 74%.
With nearly 80% of New York’s soybean farmers relying on glyphosate for weed control, the emergence of resistance is a major blow to current agricultural practices. Kumar and his colleagues are now warning farmers through outreach efforts, including newsletters, annual meetings, and one-on-one consultations, urging them to reconsider their reliance on a single herbicide.
The study also found evidence of waterhemp resistance to three additional herbicides: mesotrione, atrazine, and chlorimuron plus thifensulfuron. However, some herbicides—such as dicamba, glufosinate, lactofen, and 2,4-D—remain effective, either alone or in combination.
Despite these alternative options, researchers emphasize that simply switching herbicides is not a sustainable long-term solution. “In my education and outreach, I’m suggesting to producers that they integrate multiple, different methods of weed control, so that we’re not only relying on herbicides,” Kumar said. “That will extend the viability of the herbicides we do have.”
Among the recommended strategies are planting cover crops, selecting more competitive crop varieties, and cleaning farm equipment between fields to prevent the spread of waterhemp seeds. The team is also exploring innovative solutions, such as seed pulverization post-harvest, to limit waterhemp’s ability to regenerate.
“New York is unique in the sense that we have fewer herbicides label registered than some other states,” Kumar noted. “To sustain the options we have, we need to work outside the box.”
The study was conducted by researchers from Cornell Cooperative Extension, New York State Integrated Pest Management, Cornell AgriTech, the Connecticut Agricultural Experiment Station, and the University of Nebraska, with support from the New York Corn and Soybean Growers Association.
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