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Research at Kansas State University has found that sheep will voluntarily graze, and therefore could help sustainably control, sericea lespedeza, a noxious weed in parts of Kansas and neighboring states.
MANHATTAN, Kan. – A costly situation in the Kansas Flint Hills could become a scenario for profit, but it would require beef and sheep producers to work together to sustainably manage a noxious weed problem plaguing the area.
KC Olson, a beef cattle scientist for K-State Research and Extension, said sericea lespedeza is on the short list of noxious weed species people have thrown up their hands over, particularly those who own land in the Flint Hills. In the past, it has taken costly herbicide application to get rid of the weed.
“We have yet to learn to live with it, and we have yet to demonstrate that we can extinguish it on a large scale,” he said.
Sericea is a tannin-rich perennial legume, and cattle grazing in the Flint Hills aren’t lining up to eat it, Olson said. His latest research that examines ways to control sericea in Kansas grasslands involves two cost-effective grazing approaches: supplementing grazing cows with a corn steep liquor byproduct to prompt them to eat sericea and using sheep as "clean up" grazers on sericea once stocker cattle are removed from pastures mid-summer.
Olson said both of these methods have worked to combat the spread of sericea, although he is in the initial stages of the research. The aim is to develop additional tools for the landowner’s toolbox to help deal with this problem in cheaper ways.
A costly nuisance
Sericea lespedeza is a durable weed that costs a lot of money to get rid of with herbicide, Olson said. Sericea has been labeled a noxious weed in Kansas the last 15 to 20 years, but landowners today are no closer to making it disappear.
If a person applies chemical to it immediately, it’s possible to make it go away for a short time, he said. But, sericea is a durable plant and is allelopathic, meaning as it grows it produces chemicals in the soil that prevent the germination and growth of native plants. It’s also canopy-dominant, meaning it can shade out its plant competitors and take over a field. Landowners usually don’t notice sericea until it is out of control.
“Any airily applied herbicide will probably kill adult plants at the top of the canopy,” Olson said. “Because the tallgrass prairie has such a robust canopy structure, that herbicide does not filter down to ground level to get those juvenile plants, and it certainly doesn’t kill seed.”
The amount of seed sericea produces is another major problem, he said. One adult plant can produce massive amounts of seed, and that seed has respectable durability in the soil. Even seed that has been in the soil for several years has potential to germinate.
Supplementation for cows
Olson has been studying ways to prevent sericea lespedeza from taking over fields in the Flint Hills since 2008. To cut down on costs, he has aimed to provide more grazing pressure on the plant.
“When a plant has been grazed, the rules of nature dictate that the plant directs its nutritional resources away from seed production and toward restoration of leaf area,” Olson said. “That would be a small way we could cut into the reproductive capacity of that plant and get some control over it.”
Most of the Flint Hills’ beef stocker producers use short-season grazing where they double the stocking rate for half of the grazing season, he said. The stocker cattle begin grazing in late April to early May and are gone by mid to late-July.
Although that model has been successful for producers, it hasn’t helped control sericea, which ramps up its growth cycle about the time the stocker cattle leave, Olson said. Putting grazing pressure on sericea in August and September must be done to reduce seed production.
Olson has used supplementation of corn steep liquor, a byproduct of wet corn milling, with sericea to make it more palatable to cows that graze after the stocker cattle leave. Corn steep liquor is inexpensive and reasonably rich in protein and a compound called proline. Those two things can make animals more tolerant of high-tannin diets.
In several experiments, Olson found that this method of supplementation increased voluntary consumption of sericea lespedeza. He said downside of this method is that corn steep liquor is not available at every feed store, and it is a high-moisture product. A person must have a liquid feed handling system to use it.
The sheep method
Although sericea is not appreciated in eastern and central parts of Kansas, Olson said, in the western part of the state there is a fairly robust sheep industry. Most producers in western areas are constantly looking for available grazeable forage during the late summer months.
“We started thinking about the biology of those sheep,” he said. “They graze differently than cattle. They prefer in their diet hierarchy forbs (broadleaf plants) first, grass second and then browse (woody plants) third.”
This begged the question if mature ewes could be used in the Flint Hills to custom graze during that late season interval and help control sericea lespedeza. K-State’s Bressner Pasture in Yates Center, Kansas, consists of eight, 80-acre pastures that are routinely stocked with steers from April to July. Last year when the stocker steers left, Olson grazed ewes on half of those pastures for 60 days, from August to the beginning of October.
“We wanted to stock them at a fairly high rate, 2.5 ewes per acre for that 60-day period,” he said. “We wanted to see what they would do to that forb community during the late season grazing episode.”
Olson said three key forb species were monitored in this study, including sericea lespedeza, ironweed and western ragweed. The grazing was strictly voluntary—no supplementation was used.
“In two separate analyses during that 60-day period, between 85 and 95 percent of the sericea plants we observed showed evidence of grazing,” he said. “Not only that, but the sheep also went after the ironweed in a very big way and defoliated essentially 100 percent of the ironweed plants in those treated pastures.”
After the sheep grazed the ironweed and sericea, they turned their eyes toward the western ragweed, Olson said, and cleaned up about half of that during the 60-day interval.
When Olson went back to the pastures after the grazing interval to look at seed production on individual sericea plants, the grazed plants in the treated pasture had made little to no seed. That, he said, is crucial to controlling it. The sericea population in the untreated pastures took advantage of the late-season rains last fall and exploded in population.
This is year No. 1 of a four-year study, Olson said, so more data will be collected in the future to learn more about the sheep grazing control method.
More information about the history, characteristics and identification of sericea lespedeza is included in a publication Sericea Lespedeza: History, Characteristics, and Identification through K-State Research and Extension. Another publication explains stocking rate and grazing management for various livestock and is also available online, Stocking Rate and Grazing Management.
A video about controlling sericea lespedeza is available on the K-State Research and Extension YouTube page.