Failure to control weeds in cropland can reduce crop yields by 20-40 percent or more. K-State researchers are identifying Kansas locations with herbicide-resistant weeds. They say that knowing the extent of the problem will help them develop production strategies to help Kansas farmers.
PHOTO: Jeff Fulmer, Fields (Kan.), inspects a weed test plot.
Researchers Battle Herbicide Resistant Weeds
In an ever-present fight against weeds, Kansas farmers are pondering a future without two of their favorite tools.
The nastiest foe in western Kansas is kochia, an annual weed that has become resistant to glyphosate, the active ingredient in Roundup and many generic products. In eastern Kansas, marestail, waterhemp, giant ragweed, and common ragweed have been found to be glyphosate-resistant and frequently grow in soybean fields.
Studies at Colorado State University suggest that kochia is showing resistance to dicamba, the active ingredient in such products as Banvel, Clarity, and Vanquish.
Homeowners dislike weeds because they make landscapes unsightly, but for farmers, it’s much more. Weeds steal nutrients and moisture from the soil, cutting yields and reducing profits.
"Once a species of weeds develops resistance to an herbicide, you can't control them with that herbicide," said Phil Stahlman, weed scientist at the Agricultural Research Center–Hays. "You'll have to rely on other herbicides that may not be as effective and likely will be more expensive."
Vance Ehmke notes that some of the newer herbicides may cost as much as $30 per acre. He farms with his son, Tanner, near Dighton.
"When you start hitting a field several times a year, you just absolutely kill your profitability," Vance Ehmke said. "But the consequences of not killing these weeds are even worse than that. You could easily be looking at 20 to 30 bushels less on corn and milo. Higher inputs, lower productivity — both are bad."
By fall 2011, K-State researchers had identified numerous Kansas locations with glyphosate-resistant kochia.
"The problem is widespread throughout western Kansas," Stahlman said. "Knowing the extent of the problem will help us develop production strategies to help farmers."
"I’m really interested in what they're doing," said Jeff Fulmer who farms near Shields, Kan., and provided an acre of his land for the K-State research. "I think with the research that Stahlman did last year and with what we learned, I have a clearer plan for next year. I'm heading in a totally different direction from what I had been doing."
K-State weed scientist Curtis Thompson says certain mixes applied in very early spring (March) followed by pre- or post-emergence will control kochia, but the crop must be planted in a weed-free seedbed.
Thompson said farmers should control kochia while it's small. Once it reaches 6 inches tall, it's more difficult to control. In the case of marestail, some farmers should consider applying herbicides in fall.
"When fall weeds take off, they use a lot of moisture and become more difficult to control," he said. "Tillage may be effective; however, it thrusts some farmers back into a practice contrary to no-till, which has been very beneficial to crop production in western Kansas."
"We easily lost two decades of progress this year," Tanner Ehmke said. "For the first time in two decades, we had to till stubble. It's pretty serious."
"Herbicide-resistant weeds represent a major setback to modern farming and a major hike in costs," said Vance Ehmke. "Thankfully, we have K-State and other land-grant universities to help find answers to this problem."