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Invasive weed may be made tastier

Mary Lou Peter

By A Contributor

Like many ranchers, Bill Sproul experiences the rewards and challenges of ranching on Kansas’ tallgrass prairie. He considers sericea lespedeza the No. 1 long-term threat for ranchers like him.

Sericea lespedeza is an invasive, noxious weed that infests approximately 600,000 acres of native tallgrass prairie in the Kansas Flint Hills. Tannins in the weed hamper protein digestion by beef cattle and cause abdominal discomfort, so cattle learn to avoid it, which renders some land useless for grazing.

“Long term, I feel that it’s the biggest threat to the tallgrass prairie,” said Sproul, who grazes more than 3,000 head of cattle on his Chautauqua County ranch. “The drought is the No. 1 issue short term, but sericea is the No. 1 issue long term.”

He said ranchers have been trying to cope with the problem with chemicals for more than a decade, but that hasn’t worked. “Chemicals are part of the solution but not the whole solution,” he said.

K-State Research and Extension scientist K.C. Olson agrees. He and a team of researchers and extension agents are working with Sproul and others – some of whom are part of an organization called the Tallgrass Legacy Alliance –to control the weed. 

“One plant can produce thousands of seeds annually,” said Olson. One problem with herbicides is that they are not specific. “They kill other valuable plants, plus rugged terrain and the robust tallgrass canopy prevent chemicals from contacting immature plants,” he said.

Sericea’s invasive nature is also attributable to its ability to avoid grazing through its mildly toxic tannins. Since it isn’t eaten, it reproduces unabated.

Wildlife biologist Jim Minnerath said Olson focuses on using the weed rather than simply killing it. “His approach is probably the only long-term feasible approach,” Minnerath said.

The key is to find a safe, inexpensive supplement that could be fed to cattle to counteract the negative effects of sericea. Researchers have identified corn steep liquor (CSL), a non-alcoholic byproduct of corn sweetener production, as having strong anti-tannin properties. At the time of the study, CSL sold at about $5 per ton.

“In a series of five studies, cattle readily consumed it,” said Olson of the supplement. He said they suffered none of the digestive disorders characteristic of tannin consumption.

“If we can remove the negative consequences of tannin consumption through strategic supplementation, we can probably apply significant grazing pressure to sericea lespedeza and achieve a measure of biological control using the most economically relevant herbivores in the Flint Hills – steers and cows,” he said.

The writer works for KSU’s research and extension service.

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