MANHATTAN, Kan. -- Like many ranchers, Bill Sproul experiences the rewards and challenges of ranching on Kansas" tallgrass prairie. And 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.
"It's a major, major issue. Long term, I feel that it's the biggest threat to the tallgrass prairie. The drought is the No. 1 issue short term, but sericea is the No. 1 issue long term," said Sproul, who grazes more than 3,000 head of cattle on his Chautauqua County ranch.
"We've been working on it for 10 to 12 years with chemicals, and it's only gotten worse," he said. "Chemicals are part of the solution but not the whole solution."
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 – in looking for ways to control the weed.
"One reason for sericea's invasive nature is its capability to reproduce. One plant can produce thousands of seeds annually. We address that currently with herbicides," said Olson. But herbicides are not specific – they kill other valuable plants, plus rugged terrain and the robust tallgrass canopy prevent chemicals from contacting immature plants.
"Another reason for sericea's invasive nature is its ability to avoid grazing through its mildly toxic tannins. Without grazing pressure, sericea continues to reproduce unabated."
"[Olson's] work stands out because he's trying to figure out how to live with sericea. His approach is probably the only long-term feasible approach. If he succeeds, ecologists will be so thankful," said wildlife biologist, Jim Minnerath, who is retired from the U.S. Fish and Wildlife Service, but remains involved in the issue.
In looking for a safe, inexpensive supplement that could be fed to cattle and might counteract the protein-binding effects of sericea, the researchers 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, "and suffered none of the digestive disorders characteristic of tannin consumption."
He noted that beef cattle displayed increased acceptance of and tolerance for sericea lespedeza by supplementing with two to four pounds of CSL per day.
"That's significant," Olson said. "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. Benefits may include improved rangeland health, improved animal welfare, reduced herbicide usage, and an inexpensive and manageable control method for this plant."
More information about the research is available at http://www.ksre.ksu.edu/bookstore/ and search for ‘Cattlemen's Day sericea lespedeza."