A John Deere Publication

Closeup of hands holding blue stem grass reed

Caucasian and Yellow Old World bluestem plants are invading High Plains pastures, crowding out beneficial grasses.

Agriculture, Education March 01, 2024

Outsmart Old World Bluestem

Summer burns and timely herbicide application can beat back this problem weed.

by Bill Spiegel

Every summer, Bill Edwards spends days on a tractor, patrolling the native tallgrass prairie pastures surrounding his Olsburg, Kansas, ranch. He has one objective: eliminate Old World bluestem, a non-native, invasive grass species that is quickly overtaking beneficial native grasses.

"I think we're doing a better job of controlling it here than in most places," Edwards says. "But I think we're losing the battle."

The High Plains is home to two dominant species of Old World bluestem: Caucasian bluestem is a two- to three-foot tall, warm-season bunch grass with thin, yellow-green leaves and stems that turn white in the fall. Yellow bluestem, or King Ranch bluestem, also is light green during the summer but has fine hairs emerging around the leaf base and the yellow stems may have brownish-purple nodes. It's seedhead branchers are mostly even in length, and longer than that of Caucasian, says Keith Harmoney, range scientist at Kansas State University's Western Kansas Agricultural Research Center in Hays, Kansas.

Old World bluestem was introduced more than a century ago as a potential new forage species, and some land-grant universities planted it for research. Its ability to withstand drought quickly made it a popular choice in early Conservation Reserve Program (CRP) seed mixes in Texas and Oklahoma, Harmoney says.

When growers began to put CRP grass up for hay, the spread of Old World bluestem seemingly exploded. Seeds from the unwanted species matriculated to native grasses via wind, animals, hay bales, and vehicles. Ranchers no doubt noticed a grass that "looked a little different, but I don't think they knew exactly what it was," Harmoney says. What started as small patches of plants steadily grew. "Now we're seeing a rapid expansion of Old World bluestem," he adds.

Control measures. Research conducted by Harmoney and his KSU colleagues, Walt Fick and K.C. Olson, show three ways to suppress Old World bluestem using herbicide.

A half-pound rate of imazapyr herbicide applied at the four- to five-leaf stage, or a quarter-pound per acre at that stage and again about eight weeks later—or when the plant just begins to form a head—is effective. Imazapyr, the active ingredient in Arsenal® herbicide, will control Old World bluestem but may suppress beneficial native grasses like blue grama and buffalograss.

Or, use glyphosate at a rate of one to two pounds per acre when the plant has four to five leaves, which could be followed by another application of the same product and rate just when the plant begins to head, about eight weeks later. At these rates, glyphosate will likely kill Old World bluestem, but also beneficial grasses the herbicide contacts, Harmoney says.

Under the right conditions—low humidity and a good breeze—late growing season fire can reduce Old World bluestem, provided there is enough old residual grass dry matter to sustain a fire. In his pasture, Edwards points to an area where Old World bluestem once thrived, but a hot fire burned crowns of the plants. Native grasses now fill that space.

Above. Keith Harmoney, range scientist at Kansas State University, says herbicides can suppress Old World bluestem. Yellow bluestem is noted for its height and purple-tinged seedhead in the fall.

Grazing OWB. In some southern states, Old World bluestem is a fine forage option. "The initial growth is actually pretty high quality," Harmoney says, "but the window of quality is very short lived."

Edwards agrees, noting ranchers must stock Old World bluestem pastures at a denser rate to keep the grass short and lush. If the stocking rate is too light, the stems begin to elongate and the plants become unpalatable.

Animals tend to avoid those stemmy plants and instead concentrate on native species. Like a ripple effect, the Old World bluestem eventually proliferates.

That, according to Edwards, is the rub.

Pastures that have a little Old World bluestem—say 10-15%—and the remainder in native grass must be managed differently.

"In that case you can't stock it high enough to keep the Old World short. And then, the native grass is over-grazed," Edwards explains. "The only choice is to stock cattle at the rate you would native pasture, and then do what you can to reduce Old World bluestem with herbicides or fire.

"If it wasn't so invasive, I think it would be a wonderful grass to plant in some places, because you can graze it," he adds. "But it just doesn't stay put. That's why it is so bad." ‡