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The Challenge of Resistant Kochia

Thursday, February 1, 2024
filed under: Weeds

This photo shows kochia control, or lack thereof, in greenhouse testing at the NDSU Minot station. The kochia were planted and sprayed on February 22 with either Spartan or Valor — plus untreated check — with the photo taken 20 days later. The kochia samples came from five central and western North Dakota locations (two at Mohall), along with a susceptible kochia population. (Photo courtesy Brian Jenks)

North Dakota producers are all too familiar with kochia. It’s been one of the top three worst weeds in the state since the 1970s. Kochia is a highly competitive weed that emerges throughout the production season during cool periods in early spring or later with warm temperatures and good moisture. Kochia can significantly impact sunflower yields and, if left uncontrolled, will take over entire fields. Each plant produces thousands of seeds, and often those plants become tumbleweeds and blow across fields, spreading seeds the entire time.
“You can be the very best farmer and have your weeds under control; but if your neighbor has resistant kochia, it can blow right across the road and into your field,” says Brian Jenks, weed scientist with the NDSU North Central Research Extension Center at Minot. He adds that because the weed thrives in drier conditions, it is especially a problem in western North Dakota.
For about two decades, sunflower producers have used Aim® and Spartan® to control kochia. These herbicides have been effective in reduced and no-till systems to control weeds that are emerged and also to provide residual control. But now, Jenks affirms, some kochia has become resistant to these herbicides.

       “Some of the kochia plants have a genetic mutation that is causing the herbicide to no longer control it,” Jenks explains. “We’ve found that Aim and Spartan are still working for many producers; but they’re not working for enough that it is certainly a cause for concern. The way kochia spreads, with its tumbleweed characteristic, it’s very concerning in the coming years that it will spread very quickly.”
        Jenks and his team ramped up their research on this issue in 2023, with funding from the National Sunflower Association. They’re looking at crop tolerance and kochia control in sunflower with herbicides other than Aim and Spartan, hoping to find an alternative that will work for kochia control.
        Of course, all that research takes time. Jenks says they’ll repeat the research again this year and add a few more facets to their work. But even if they find viable alternatives, it could still be several years before new herbicides are labeled and approved for use in sunflower.

        In the meantime, Jenks says producers should stay diligent and keep a close eye on kochia in their fields. If kochia is resistant, he says it might be best to go back to the old chemistry herbicides.
        “Before Spartan, we used products like Treflan, Sonalan and Prowl,” he points out. “The problem with Treflan and Sonalan specifically is that they need to be incorporated through tillage — and most producers in western North Dakota have gone to no-till, which means they can’t be used or must be incorporated another way. However, they are available in granules that could be applied in the fall once temperatures drop below about 55 degrees. Those granules get incorporated into the soil over the winter. This method doesn’t provide perfect control, but it’s better than nothing.”
        Prowl can be applied in the spring, but also won’t provide 100% kochia control. Jenks says the problem with spring-applied Prowl is that it needs a lot of rain to activate before the weeds emerge. If the weeds emerge before the rain, the herbicide will not work.
        “I’m telling farmers: ‘The sky isn’t falling,’ but you need to be aware of this potential problem and monitor how effective your kochia burndown is in the spring,” Jenks emphasizes.
        The NDSU weed scientist is also telling producers to be extra diligent with controlling kochia in other crops, noting that there are more herbicide options available for crops like wheat, soybeans and corn than there are for sunflower. Jenks says getting kochia under control in those crops could set fields up better when the rotation calls for sunflower.

As any farmer in ‘kochia country’ knows, the tumbleweed effect can result in weed seeds from a neighbor’s field being deposited on your ground. If they’re resistant to commonly used herbicides, that becomes ‘your’ problem. (Photo: Phil Westra)

And there is work being done at the National Agricultural Genotyping Center in Fargo that Jenks says could soon offer help to producers. Researchers there are developing a rapid test that will determine whether kochia has the mutation that makes it resistant to Aim and Spartan. The idea is that a producer could send in two leaves from a kochia plant, and within just a couple of weeks the genotyping center would be able to tell them if it is resistant. The center has already developed similar testing for waterhemp and Palmer amaranth, Jenks is hopeful the kochia test could be ready by this spring.
“That would be a pretty great deal,” Jenks says. “It would cut down significantly on the time farmers wait to find out if they have resistant kochia. Right now, it takes several months. Soon, we could have answers within just a few weeks. That could be a game changer for producers as they fight this weed.” — Jody Kerzman