KSU researchers say fall burning impacts weeds

Kansas State University researchers have completed a four-year study that shows late-summer burning dramatically reduces the incidence of the noxious weed sericea lespedeza in the state’s pastures.

As much as one-third of the Kansas prairie is already influenced by sericea lespedeza.

If widely implemented, shifting to late-summer burning could increase cattle-production income by as much as $50 million a year in eastern Kansas.

KC Olson, animal sciences and industry professor who led the study, has data to show incidence of sericea lespedeza is higher in pastures burned in April than those burned in August and September. The findings could change the way ranchers typically manage their pastures. It is a long-held custom to burn pastures in April in Kansas.

“What I do know for sure is that spraying those plants does not work,” said Joe Hoaglund, who manages J&N Ranch near Leaven­worth. He said his operation has been trying to control sericea lespedeza by spraying it for the past 20 years, and it just keeps coming back.

“I saw the research from K-State, and it looked promising,” Hoaglund said. “The big thing is retarding the seed. I’m not so sure that burning has an effect on the plants that you have in the field right now, but it may stop the next generation and eventually those plants will die completely.”

Sericea lespedeza was classified as a noxious weed in Kansas in 2000. The plant is known to out-compete native plants for water and nutrients, and it contains high levels of condensed tannins that make it undesirable for cattle grazing the land—which means they rarely eat it.

Tannins are naturally occurring compounds that bind protein in the gut of ruminant animals, preventing the animal from digesting protein. By reducing the incidence of sericea lespedeza, cattle will be able to graze pastures and more efficiently convert that feed into energy. As a result, they will grow more efficiently.

Olson said recently that the estimated net income from improved cattle growth in the Flint Hills is between $20 million and $50 million annually. Burning in the fall could also reduce the need for herbicide applications, which costs an estimated $2.75 to $82.28 per acre, according to Olson.

Olson said researchers chose to investigate off-season fires because they thought it would be compatible with intensive early stocking, as is practiced in the Flint Hills.

After just one year of burning, sericea lespedeza failed to make seed. After the third year of burning last year, the number of plants in the field fell dramatically, according to Olson.

“That means we are controlling the vegetative spread of the plant,” Olson said.

Hoaglund said he has just completed his second year of late-summer or early fall burning. In 2016, he burned on Oct. 1, but this year moved it up to the first two weeks in September.

Olson is planning to build upon the four-year project with future studies on how best to integrate late-summer fire into cow-calf and yearling production systems.

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