In a roomful of weed-weary farmers, Marshall Hay preached to the unconverted.

The Kansas State University agronomy graduate student told of how he walks countless fields in the spring where producers failed in their burndown because they were using only glyphosate. For a weed scientist to see farmers make the same mistakes is frustrating.

“Folks, I have a message for you,” he said. “The solution to our herbicide resistance issues is not going to come from a jug. Because, guess what, there are not any new jugs to be had. It’s over.”

The battle to control crop-choking weeds is being fought across almost every farm field across the nation. Fast-growing weeds like kochia and palmer amaranth—or pigweed—are defying even multiple douses of top-selling herbicide Roundup whose primary ingredient is glyphosate.

There are several other herbicides that aren’t as effective today, Hay added, including HPPD and atrazine. For now, producers must look at other options, which includes using integrated strategies to manage weeds.

Pigweed 101

Pigweeds are hardy plants, Hay said, giving the crowd a pigweed 101 lesson.

The pigweed is native to the southwestern United States. It is well adapted to dry conditions.

Pigweeds have a rapid growth rate that peaks in the summer. “When sorghum is shutting down because it is over 100 degrees, pigweed is ramping up,” he said. Palmer amaranth doesn’t reach its maximum level of photosynthesis until 120 degrees Fahrenheit. 

Each pigweed has its own genetic makeup. “Just like we have our own DNA, the same thing goes with pigweeds. They have different characteristics and different strengths,” Hay said. “I can’t think of any weeds more competitive than pigweed.”

He stressed three key takeaways to farmers: How to use cultural practices such as cover crops and row spacing to manage weeds; how herbicide resistance works; and how to develop a management plan regarding herbicide use and weed control. 

Don’t believe everything you hear

While widespread glyphosate resistance is the norm, no herbicide is safe from resistance.

Herbicide resistance, Hay said, results from random genetic mutations. Thus, that weed will survive an application of glyphosate.

Do that a few times and the only ones left in the field are the resistant weeds.

But don’t believe everything you read on Twitter or hear from the neighbor—high pH, drought stress and dust aren’t causing resistance.

“A lot of producers might have a misnomer that herbicides create herbicide resistance,” Hay said. “It’s actually the exact opposite. We create the herbicide resistance by using that herbicide inappropriately. Herbicides don’t cause mutations. Herbicide resistance is always linked to a genetic trait.”

Meanwhile, low dose selection can happen, but for most of the state’s cropping systems, it isn’t at the forefront of the issue.

“It is more about using that repeated selection year after year—to select for those biotypes that have the genes that can confer that resistance genetically,” he said.

Finding a solution

He said farmers should develop a herbicide plan that includes multiple, effective sites of action.

For instance, tank mixing is better than rotating, he said. “We know it is more effective if you can put two effective herbicides together,” he said, adding farmers should scout their fields routinely.

Hay also researched different weed management strategies at three separate locations last year. The study included three different row spacings—30-inch, 15-inch and 7.5-inch rows. Some of the studies incorporated cover crops.

However, planting narrow rows isn’t the solution, either, he said.

“We have to have a herbicide out there to control the weeds,” he said.

Amy Bickel can be reached at 620-860-9433 or

(1) comment


Good Morning, My name is Dave Button, we farm in central Kansas where we have been battling herbicide resistant weeds for several years. Rather than wait for the 'next big thing' in herbicides, (which, by the way, isn't on the horizon, too many $$$s to develop) we decided to take on weed control ourselves and have been quietly developing a machine that we just received a US Patent on to control herbicide resistant seed production. Our Row Shaver is designed to clean weeds from between the rows of any crop planted in 30 inch rows. The machine can be adapted to narrower rows in the future. Our demo unit is mounted on the front of a Hagie 284 sprayer tractor (front mount is a must to prevent the wheels from trampling weeds before the Row Shaver does it's job) and is just about ready for use in the 2019 season. We grow corn, milo and soybeans, so we want to test our demo unit on our crops this summer to be sure it works as designed. To kill grasses and 'micro' weeds that grow between crop rows, we have installed a hooded sprayer on the rear of each row unit where good 'ol glyphosate, gramoxone, ect. can be used. Or, if you need more fertilizer on the crop, drop tubes are installed on the rear of the hood to direct fertilizer where needed.
To control seed production on weeds that grow within the crop rows itself, the Row Trimmer is designed to float just above the crop canopy and cut off seed pods and flowers (sunflowers, velvet leaf, and even pigweeds) that extend above the crop. Again, we are trying to reduce the herbicide resistant seed bank, not necessarily kill the weed itself. After a few seasons of using our system, we feel we can at least get a handle on our resistant seed population in either no-till or organic crop systems.
Our website,, will be populated with photos and videos once the demo unit is up and running, All of the current content on the web site is out of date, but we will be updating soon (whenever it quits raining!). Any questions can be directed to myself at 316-516-2477. Thanks and we hope to be helping farmers soon!

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