For many farmers, glufosinate quietly became the last dependable post-emergence option to control tough broadleaf weeds like waterhemp in fields where glyphosate, ALS, PPO, and HPPD herbicides had already slipped in performance. Glufosinate’s “last herbicide standing” status is why what’s happening in Illinois now should grab your full attention.
University of Illinois weed scientist Patrick Tranel and his colleagues announced in December that they have confirmed several glufosinate-resistant waterhemp populations in Carroll County, in northern Illinois.
That confirmation is a big deal. Boiled down, what this means for Illinois farmers is stark: Every post-emergence herbicide available to control waterhemp in the state—seven different herbicide groups—is now compromised to some degree.
Tranel adds that some preemergence chemistries are also declining in efficacy. How that plays out in fields: he says pre herbicides that might once have provided four weeks of residual control now keep weeds in check for only three weeks.
“Let that set in for a moment,” he says. “That means we can’t just go out there and say, ‘Oh, I’m going to use this herbicide to control waterhemp.’ You might not have resistance in your field yet to that particular herbicide, but it’s out there in the state, and if you rely on that single post product, you are going to get resistance.”
Farmers in states outside Illinois aren’t off the hook, either. The problem of glufosinate-resistant waterhemp is suspected in at least six other states including Missouri, Indiana, Iowa, Nebraska, Ohio and Tennessee.
“Missouri farmers are facing declining control of waterhemp with two of our most common post products—glufosinate and 2,4-D—and that continues going into 2026,” says Kevin Bradley, University of Missouri Extension weed scientist.
Why Waterhemp is a Driver Weed
Waterhemp is considered a “driver weed” for many row crop growers across the Midwest and South due to its ability to severely impact yields.
- Yield Losses: Uncontrolled populations can cause extensive yield losses—up to 74% in corn and 56% in soybeans—according to research by Larry Steckel, University of Tennessee Extension weed scientist.
- Dominance: In the 2025 Weed Science Society of America (WSSA) broadleaf crops weed survey, waterhemp surpassed Palmer amaranth (pigweed) as the most problematic weed.
- Biological Challenge: The reasons for waterhemp’s dominance include prolific seed production (up to 1 million seeds/plant), season-long germination, rapid growth, dioecious nature (male/female plants for high genetic diversity), and widespread resistance to multiple herbicide sites of action (SOA).
One Of The Challenges: Subtle Resistance and Regrowth
Tranel calls what Illinois researchers are seeing the early stages of resistance evolution. Critically, what they observe isn’t the obvious kind of resistance where the herbicide does nothing. This low-level resistance makes it difficult to detect in the field.
“It looks the same as what the symptomology looks like on a glufosinate-sensitive plant, except not as severe… you’re going to see that burning, but you’re not going to see the continued progression of that control,” Tranel says. “You’re going to start seeing regrowth.”
In Illinois field trials, resistant plants were sprayed small, with full rates, under near-perfect conditions (hot, humid, sunny, with ample soil moisture), and still, some waterhemp survived.
Tranel’s research suggests some resistant plants may be able to detoxify glufosinate faster at higher temperatures:
“We saw actually worse control of the resistant population under higher temperatures… we think that’s because the resistant population is able to metabolize or detoxify the glufosinate, and at higher temperature it’s able to do that faster,” he says.
Bradley agrees, reporting similar scenarios in Missouri. This low-level resistance can be easily confused with application issues, which makes confirmation difficult. Farmers often report poor glufosinate control due to weeds that were too big, poor spray coverage under a canopy, or less-than-ideal temperature and humidity.
“It can be difficult to distinguish between, ‘Do I really have a resistant population, or was my application not quite right?'" Tranel explains.
The Harsh Reality: No Chemical Safety Net Left
The urgent message for farmers is that they can no longer rely on any single product to deliver control of waterhemp and other tough weeds. Furthermore, the old rule of simply rotating sites of action is no longer sufficient.
“Fifteen years ago, almost all our resistance was due to target site change,” Tranel explains. “All the new mechanisms we’ve discovered in the last 15 years have been due to mechanisms other than a target site change.”
This shift in the plant’s biology means that merely switching group numbers will not keep growers ahead of waterhemp for long.
“You can’t manage chemical resistance with chemicals,” Tranel says. “We cannot exclusively rely on herbicides like we have been able to do in past decades.”
Strategies for the Long Haul: Don’t Cut Weed Control Rates
Farmers face going into the 2026 season with paper-thin margins. During a recent farmer panel discussion, Kevin Bradley asked several high-yield Missouri growers what keeps them up at night.
“Every single one of them said input prices,” he recalls. “Many of our growers are just doing what they believe they have to do to be able to stay on their land and farm. The problem is we are just seeing more performance failures with our post herbicide products that we rely on now,” he adds.
Bradley and Tranel are concerned about farmers choosing to trim herbicide programs. They both strongly recommend that farmers use full rates of herbicides, especially in fields with tough weed issues. Cutting herbicide rates will save few if any dollars.
“With glufosinate, we’re talking pennies between lower and full rates. It’s not going to be a whole lot of money to get better control of weeds and prevent them going to seed,” Bradley says.
Diversify and Aim for Zero Seed
Glufosinate must be treated like a valuable resource. The weed scientists encourage farmers to protect it by making every application as effective as possible and reducing the number of weeds it has to kill. Key practices they recommend include:
- Use Multiple Products: Tranel advises against leaning on a single post-emergence herbicide. Instead, “use two or more, either tank mixed or in sequence,” and use an overlapping residual.
- Integrate Non-Chemical Tools: Practices like using cover crops that produce significant biomass can suppress waterhemp and other weeds, reducing the number of weeds that ever see a spray pass. New technologies such as weed zappers, harvest weed-seed management products, and weed flamers are also gaining traction. As these options prove viable, they give producers additional tools to the current chemical options for weed control, notes Matthew Woolard, WSSA Science Policy Fellow and Texas Tech University graduate assistant.
- Have a ‘Zero-Seed’ Goal: The ultimate long-term strategy is to deplete the soil seed bank. “At the end of the growing season, if you don’t have a weed going to seed, you’re not going to get evolution of resistance,” Tranel says. Achieving this goal will reduce pressure on your herbicide program.
Tranel says he sometimes ponders where the farming community would be today with regard to weeds if glyphosate had been stewarded better. It’s a lesson he hopes row crop growers take to heart.
“Glufosinate might be the best thing we have for the next 10 years. How can we make sure we can keep using it for the next 10 years?” Tranel says.
The answer is not more glufosinate use on its own. Better systems—using multiple SOA products, more crop diversity, more scouting, and allowing fewer escapes to go to seed—can help keep the chemistry in play.
Bottom line: The clock on glufosinate is already ticking down, and how fast it runs out is now largely in farmers’ hands.
