While scouting a no-till field adjacent to his East Troy, Wis., research plots in 2021, independent research agronomist Jim Stute made a concerning discovery.
“A giant ragweed plant survived the first-ever application of Enlist on my farm,” Stute says. “Its neighbors were twisted, turning yellow and dying. Its response was to turn darker green, and the leaf margins, instead of being deeply lobed as I'd see in a typical plant, were fused.”
Stute took this photo of the plant to document its reaction:
METABOLIC RESISTANCE? Independent research agronomist Jim Stute took this picture of a giant ragweed plant that survived an initial Enlist application, despite neighboring ragweed plants turning yellow and dying. Note the fused leaf margins. “There’s some kind of reaction going on in this plant,” Stute says. “My fear is that this is not just resistance to Enlist but overall metabolic resistance.”
Based on the fused leaf margins and deeper green leaf color, Stute feared the plant had developed overall metabolic resistance, not just resistance to Enlist. Weeds with metabolic resistance are able to break apart the chemistry of herbicides across herbicide groups triggered by exposure to just one herbicide. This renders the herbicide inactive and keeps the weed healthy.
The concern stemmed from recent confirmation of glyphosate resistance within a group of plants sampled from within the same area by University of Wisconsin-Extension weed scientists. Other plants, while not resistant to glyphosate, showed resistance to either cloransulam or fomesafen.
“If we develop metabolic resistance, suddenly the plant can metabolize everything,” Stute says. “If that's the case, it's game over as far as chemical weed control.”
In a future where metabolic resistance threatens mix-the-mode weed control, cover crops could become a critical tool to combat herbicide-resistant weeds. In 2024, Stute concluded a 4-year trial assessing if cereal rye could be used to suppress herbicide-resistant marestail, waterhemp and giant ragweed, and the best time to terminate the cereal rye cover to maximize weed suppression while also minimizing yield.
“It’s a tool to supplement the traited packages and to prevent the development of widespread resistance,” Stute says.
If you'd like to watch Stute’s presentation from the 2025 National Cover Crop Summit about the termination "sweet spot" and more, register for the 2026 National Cover Crop Summit All-Access to receive full access to the video archives!
