Sheep grazing may clean up sericea

Sheep grazing may clean up sericea

Research finds that sheep will voluntarily graze and could help sustainably control noxious weeds.

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 Kansas State University Research & Extension, said sericea lespedeza is a hard-to-manage noxious weed species, particularly for people who own land in the Flint Hills. In the past, it has taken costly herbicide applications to get rid of the weed.

Sericea lespedeza is a durable weed that has been labeled a noxious weed in Kansas for the last 15-20 years, but landowners today are no closer to eradicating it, Olson said.

"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.

If chemical is applied to the weed immediately, it's possible to make it go away for a short time, he said. However, sericea is not just durable but allelopathic, meaning that as it grows, it produces chemicals in the soil that prevent the germination and growth of native plants. It's also canopy dominant, meaning that it can shade out its competitor plants and take over a field.

Sericea is a tannin-rich perennial legume, but cattle grazing in the Flint Hills aren't lining up to eat it, Olson said.

His latest research into ways to control sericea in Kansas grasslands involves two cost-effective grazing approaches: (1) supplementing grazing cows with a corn steep liquor byproduct to prompt them to eat sericea (2) and using sheep as "cleanup" grazers on sericea once stocker cattle are removed from pastures in midsummer.

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 landowners can use to help deal with this problem in cheaper ways.


Grazing trials

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 put 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 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 at about the time the stocker cattle leave, Olson said. Grazing pressure must be applied to sericea in August and September in order to reduce seed production.

Olson noted that there is a fairly robust sheep industry in the western part of Kansas, and most sheep producers in western areas are constantly looking for available forage for grazing during the late-summer months.

Noting that sheep graze differently from cattle, Olson wondered if mature ewes could be used to custom graze in the Flint Hills during that late-season interval and help control sericea lespedeza.

Kansas State University's Bressner Pasture in Yates Center, Kan., consists of eight 80-acre pastures that are routinely stocked with steers from April to July. Last year, after 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, so no supplementation was used.

"In two separate analyses during that 60-day period, between 85% and 95% 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% of the ironweed plants in those pastures."

When Olson went back to the pastures after the grazing interval to look at seed production on individual sericea plants, the grazed plants had made little to no seed, which he said is crucial to controlling it. The sericea population in the non-grazed pastures took advantage of the late-season rains last fall and exploded in population.

This is the first year 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.

Volume:86 Issue:23

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