It’s the basic tenet of ranch management. The healthier and more diverse the pasture ecology, the more grass that is grown. More grass grown equals an increase in carrying capacity of the pasture.

Battling invasive species such as sericea lespedeza with fire is one way to put that pasture ecology back on track for balance, according to KC Olson, Kansas State University professor of range beef cattle nutrition and management. And making sure you time that prescribed burn correctly is key.

Olson spoke about rethinking pasture burning plans at the 2024 K-State Stocker Field Day in September, held at the Beef Stocker Unit, Manhattan. Kansas producers raising cattle in the tallgrass prairie ecosystem have been battling invasive sericea lespedeza practically since its introduction in the 1930s as a fix for strip-mined ground in the southeast.

Today in Kansas, about 450,000 acres are affected by sericea lespedeza in the eastern half of the state, Olson said. Nationally, it can be found all through the eastern half of the U.S., from Florida to Ontario and from the Great Plains to the Atlantic Coast. And where sericea lespedeza grows unchecked, choking out beneficial forbs and grasses, biodiversity suffers.

Take Greenwood County, Kan., where the Kansas Department of Agriculture reports that 82,000 to 103,000 acres of the county’s 740,000 acres are drastically affected by sericea lespedeza infestation.

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“If sericea lespedeza was not in Greenwood County, there would be room for 27,000 to 34,000 more 90-day yearlings on grass,” Olson said. “On a gross income basis, that’s $2.7 million to $3.4 million per year taken out of our communities.” If you run the numbers for a cow herd in the same footprint, Olson added, you could run up to 7,300 more cows, for a net of $500 per pair, or a total of upward of $3.7 million given up per year in Greenwood County.

That’s just one county in one state. Sericea lespedeza’s cost to cattle producers across the prairie states and the eastern half of the U.S. is magnified. But so far, control has been hit or miss.

Fall burns

“We’ve tried herbicides, cattle supplements, even sheep and goats to graze it,” Olson said. “They’ve worked to some degree, but they aren’t commercially feasible.”

Then he had the spark of an idea — controlled burns in the late summer and early fall. The data from a 17-year study shows that fire can work.

“If we put fire on sericea lespedeza at the right time, we take away its competitive advantages,” Olson says. Those advantages include:

Related:Be wary of overgrazing pastures this fall

The average stem can produce 711 seeds, which are so durable they can last in the seed soil bank for 70 years, and can be spread by rain and human interaction.

Cattle producers in the Flint Hills have long adopted spring burns in late April to rejuvenate the tallgrass prairie in time for the grazing season. What Olson proposed was a burn treatment in early August and again in early September. The initial findings were significantly better than expected. By burning in early August, the plant was down to just 3 seeds per stem, and that number dropped to zero with the early September burn treatment. Even better, the individual plants that remained after those August and September burns were smaller and less able to reproduce, he said.

By burning between Aug. 1 and Sept. 15, Olson found other invasive species were controlled as well, including caucasian bluestem, yellow bluestem, ironweed and perennial ragweed. That allowed beneficial legumes and wildflowers to increase up to threefold. “All those little plants needed was an opportunity, a sericea lespedeza-suppressed environment, and they took it,” he explained.

DIFFERENT: Unlike a typical prescribed fire in the spring, a summer or fall burn will move more slowly and leave more residue.

The native and cultivated warm-season grasses and their root carbohydrate stores are unaffected by the fall burn plan, and cool-season grasses aren’t stimulated by fire. However, the higher ambient temperatures of the fall fire timing can more easily kill woody-stemmed plants.

Related:6 ways to reduce summer slump on pasture

A fall prescribed burn takes some planning. First, you need to defer the spring fire to ensure there’s enough fuel. The surface litter should cover 30% to 40% of the soil surface, Olson advised, to carry the flame. Expect to use more ignition fuel and to repeat the treatment several times, and the smoke may be dense because of the higher possible water content in the plant material. Also, and this cannot be stressed enough, follow all safety rules you would follow in a spring practice.

Olson said you should expect significant plant material to remain after a late burn, unlike what you’d see in a spring burn. What’s left, he said, will generally top-kill in two days and begin regrowth.

SMOKE: The timing of a later fire application can help cattle producers recover their pastures from invasive sericea lespedeza, and improve overall rangeland health.

Cattle response

But what about carrying capacity and timing of grazing with a fall burn? That can be an initial trade-off. Olson said there is about a 10-pound reduction in stocker cattle weight gains by the time short-season stockers are shipped in August on a fall fire plan compared to an April plan.

But consider the time and money spent spraying herbicide that isn’t as effective, Olson added. The average cost to apply herbicide, depending on the product used, can be from $17 to $62 per acre. Using data from the KSU Beef Stocker Unit, with a target of 250 pounds of live weight from stockers grazing pasture, he figures a revenue loss of about $5.50 per acre from the reduced weight gains. Even with the revenue loss from reduced gains, the savings from not applying herbicides were roughly $11 to $56 per acre, he said.

Saving money and time, plus improving the biodiversity and long-term health of the range may be worth considering a change in strategy for some cattle producers in the fight against invasive species.