By Blake Jackson
Cornell University researchers have confirmed that waterhemp, a highly destructive weed, has developed resistance to glyphosate in New York state.
This finding, published in Weed Technology on January 13, 2025, highlights a significant challenge for U.S. growers.
The study revealed that waterhemp samples from Seneca County soybean fields were five to twelve times more resistant to glyphosate than control samples.
Researchers also identified other effective herbicides and evidence of resistance to additional chemistries.
“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. “Along with Palmer amaranth, waterhemp is one of the worst species in the country right now, and we already have reports from midwestern and southern states of resistance to many different herbicides. We need to educate folks and get ready in terms of management.”
This research marks the first confirmed case of glyphosate-resistant waterhemp in New York, where 75% to 80% of soybean farmers rely on glyphosate for weed control.
Waterhemp, known as a “superweed” for its rapid proliferation and resistance evolution, has spread to 23 New York counties since its discovery in 2014, posing a threat to soybean and corn yields.
Kumar and his team are now educating growers about the need to move beyond glyphosate, through meetings, publications, and consultations. They also found evidence of resistance to mesotrione, atrazine, and chlorimuron plus thifensulfuron, while dicamba, glufosinate, lactofen, and 2,4-Dichlorophenoxyacetic acid remain effective.
Given waterhemp’s ability to develop multiple resistances, Kumar advocates for an integrated weed management strategy. “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,” he said. “That will extend the viability of the herbicides we do have.”
Strategies include planting cover crops, using competitive crop varieties, and cleaning equipment to prevent seed spread. Researchers are also exploring new techniques, like pulverizing waterhemp seeds post-harvest, and monitoring resistance across the state.
“New York is unique in the sense that we have fewer herbicides label registered than some other states,” Kumar said. “To sustain the options we have, we need to work outside the box.”
Categories: New York, Crops, Education