Herbicide-resistant weeds aren’t just a here-and-there nuisance in the Midwest anymore. From herbicide-resistant waterhemp to Palmer amaranth (pigweed), ragweed and ryegrass, more farmers are seeing them and finding they can shrug off nearly anything sprayed to control them. That’s the reality the new HERMON project is built around.
HERMON stands for Herbicide Resistance Monitoring Network. It’s a multi-state effort funded by a United Soybean Board grant and led by Eric Patterson, Michigan State University weed geneticist.
The idea is to connect farmers, university weed scientists, and diagnostic labs in a way that finds herbicide resistance in weeds sooner, figures out what’s contributing to it, and turns those insights into useful recommendations to help farmers address the problem in their fields before it gets totally out of hand.
Moving Beyond The Gold Standard
Patterson says that until now, the way resistance was confirmed has been slow and clunky. It usually starts when a farmer spots a patch of weed escapes and suspects something more than a sprayer skip.
“You’re looking at plants coming [into a lab] in the fall, getting screened all winter long, and growers not having the results until the spring,” Patterson says. “Growers [are] already putting out pres when they’re learning about what resistance they have in their field.”
Patterson calls that traditional “whole-plant greenhouse work” the gold standard for the industry, and he’s not looking to throw it out. But HERMON is providing faster testing methods and results in addition to that, so farmers aren’t always waiting months for answers.
One of the big tools weed scientists are leaning on is DNA testing. Any time a weed evolves resistance, there’s some sort of change in its DNA. If researchers know what mutation to look for, they can test for that directly.
“If we can do enough research and know what all of those mutations are, we could technically just screen for those mutations and use that as a proxy or as a marker that that plant is likely to be resistant,” Patterson explains.
The DNA testing already works well for certain types of resistance, he adds, like for Group 2 ALS (acetolactate synthase) inhibitors and a lot of glyphosate-resistant waterhemp and Palmer amaranth.
“We know that target site for pretty much every major weed, so we can just sequence up that gene and it either comes back ‘yes or no,’” Patterson says.
However, DNA tests aren’t a perfect solution.
“We can usually confirm that something would be resistant, but we cannot confirm that it would be susceptible,” he says.
There can always be a new mutation or a different mechanism, especially with more complicated metabolic resistance. Still, DNA-based tests can often get an answer back in three or four weeks.
HERMON researchers are also working on other practical lab tests. One promising approach is called a leaf-disk assay.
“You take a little bit of a leaf [called a disk] and soak it in a herbicide, and then you can kind of monitor the health of that leaf, and you can compare that to a leaf disk that was not put in the herbicide,” Patterson says. Researchers use a camera or scanner to measure how green the disks stay. For contact herbicides like glufosinate and many PPOs, this can give a good read on whether a specific weed population is resistant.
“This is kind of the intermediate between going fully into DNA, but still being able to do something in the lab that helps you monitor things quickly,” Patterson says.
Breaking Down The Walls
HERMON bridges 10 land-grant universities across states like Illinois, Indiana, Kansas, Arkansas, and Mississippi. The goal is a transparent exchange of data and weed populations.
“We’re trying to share those resources with each other and not hoard them or sit on them,” Patterson notes. “I think there’s been many, many walls between different groups that if we can reduce those barriers, we can have better monitoring.”
Joe Ikley, North Dakota State University Extension weed specialist, has already seen the value of collaboration. By working with industry partners like BASF on a rapid test for PPO-resistant kochia, his team identified many resistant populations in a fraction of the time it might have taken before now.
“If we’d had to do this the old-fashioned way to find the mutation two years ago, we might be talking only 10 populations we know of versus a couple hundred,” Ikley says.
Proactive Management for the Future
Looking ahead, Patterson sees HERMON as a starting point for something that could be used across the U.S. “I kind of see HERMON as a test balloon to see if there is interest in a fully nationalized project where resistance monitoring becomes kind of an established thing that every state and every land-grant university contributes to,” he notes.
Sarah Lancaster says the opportunity to have a platform where weed specialists can share information across a state or area about resistant weed populations and their location could be a game changer for farmers.
As she puts it, if a Kansas farmer in one county knows there’s confirmed resistance just a county or two away, “[they’re] going to be more vigilant and more proactive” with herbicide selection, trait choices, and overall weed management, says Lancaster, Extension weed scientist at Kansas State University.
While HERMON offers hope that resistance can be addressed better and faster in the future, no one involved in the project is expecting to develop a miracle product that resets weed control. As Ikley jokes, “Silver bullets are for werewolves, not for weeds.” Instead, the goal is to tighten the loop between what farmers see in the field and what scientists can confirm in the lab, so growers get earlier warnings and better information to protect the herbicides they still have available.
Patterson notes that in corn, there are still several chemistries for farmers to move between. But soybeans don’t have that luxury.
Growers end up “putting a lot more pressure on PPO inhibitors, as well as some of the new traits that are coming out,” Patterson says. The scary question he and other researchers ask is, “What happens when there are no viable herbicides left, and how do you manage that?”
With help from HERMON, researchers hope to not have to answer that question anytime soon.
For additional insights on HERMON, check out the War Against Weeds podcast, featuring Patterson and hosts Sarah Lancaster and Joe Ikley. The podcast was promoted by GROW (Getting Rid of Weeds), a scientist-led network coordinating research to help farmers across the U.S. fight herbicide resistance.
