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Herbicide-Resistant Kochia in N.D. Sunflower Fields
Saturday, February 1, 2025
filed under: Weeds
Greenhouse tests at NDSU-Minot for herbicide effectiveness on resistant kochia.
Obviously, not all of the herbicides here are labeled on sunflower.
— The Challenge Continues —
It’s been said — including by weed scientists such as North Dakota State University’s Brian Jenks — that the best herbicide for kochia “is rain.” That’s uttered with tongue in cheek, of course, but the point is valid: kochia grows best under dry conditions, not wet.
The conundrum for producers is that while droughty conditions may limit kochia emergence and growth, they simultaneously limit crop development and yield — thus the interest in and need for herbicides that hold kochia at bay, regardless of moisture conditions. That’s particularly important when a producer is plagued with herbicide-resistant kochia in his fields, as has become the case in a large swath of North Dakota.
Jenks, who is stationed at NDSU’s North Central Research Extension Center near Minot, has been focused on finding answers to resistant kochia for the past several years. As it thrives in drier conditions, the weed is a particular challenge in central and western North Dakota, where average rainfall is significantly lower than in areas to the east, like the Red River Valley.
Brian Jenks
Another aspect of the kochia challenge, Jenks notes, is its propensity to spread from property to property with the wind (hence the old term “tumbleweed”). “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 fields,” he points out— a reality all too familiar to many growers.
For a number of years, of course, glyphosate was the go-to burndown treatment for kochia control in sunflower fields and other crops. Then kochia populations resistant to glyphosate developed and spread, prompting the need for alternatives.
More recently, sunflower producers have commonly used Aim® and Spartan® to control kochia. These two herbicides proved quite effective in reduced- and no-till systems to control emerged weeds as well as providing residual control. Unfortunately, of late we’ve been experiencing the development of kochia populations that are resistant to these herbicides as well.
“We’ve found that Aim and Spartan are still working for many producers; but they’re not working for enough, to where it’s certainly troubling,” Jenks reports.
In 2023, Jenks and his team ramped up their research on resistant kochia in part with funding from the National Sunflower Association. Along with evaluations of Aim and Spartan kochia control in sunflower, they began looking at crop tolerance and kochia control levels in sunflower with additional herbicides, hoping to find effective alternatives. Some of those products are available for sunflower; others are not currently labeled. This research continued in 2024 and will be conducted again in 2025.
(Sunflower crop injury results have been very encouraging. In 2023 and 2024 trials at Minot, with three different planting dates, there was zero crop injury with any of the herbicides under evaluation.)
So how should sunflower growers dealing with resistant kochia proceed as of the 2025 growing season?
Jenks points out that resistance to Group 14 herbicides (e.g., Aim, Sharpen, Vida®, Reviton®, Valor®) is not present everywhere — but growers and crop consultants still need to monitor for it, regardless of location. He also advises rotating among different burndown products where possible (i.e., Sharpen, Aim, Roundup, Gramoxone and, in certain circumstances where labeled, Dicamba). “Monitor effectiveness three to seven days after treatment,” he says.
If kochia control appears poor, Jenks recommends sending in leaf samples to the National Agricultural Genotyping Center in Fargo for quick and accurate validation. Learn more about the center’s services at www.genotypingcenter.com.
Finally, the NDSU weed scientist urges extra diligence with kochia control in other rotational crops, such as wheat, corn and soybeans, where there are more herbicide options. Effective kochia control in those crops will help keep this weed in check once the field goes into sunflower.