King Ranch bluestem, Bothriochloa ischaemum (L.) Keng, was introduced from China into California, and then onto the King Ranch around 1924. Potential benefits at that time were grazing tolerance, rapid growth and forage quality. The plant is a bunchgrass that grows 18-48 inches tall. The stem turns a yellowish straw color when mature. Each stem produces a loose terminal seed head that is maroon or purple. The warm-season grass flowers in early summer and is winter hardy.
When introduced on the King Ranch, the grass quickly moved out of the ranch and has since invaded most areas of Texas and Oklahoma. In addition to being used for livestock grazing on the ranch, the grass was used for erosion control, which helped it spread. An aggressive grower, it outcompetes many more desirable kinds of grass and has since been considered invasive, as it threatens the abundance and diversity of native grass species.
Coming into the office this week, I noticed the grass all along FM455. In mid-October in Denton County, you can see the grass about 3 feet tall with purple seed heads. The thin stems are very poor forage for livestock, even though it looks tall and abundant. Other concerns related to the grasses’ effect on the rangeland include diminished bird diversity, reduced insect diversity, and rodent populations.
Tilling, herbicide use, prescribed fire and intensive grazing are all management options, but eradication can be tough. If you do decide to manage the grass, it is best to have a multifaceted treatment plan that includes herbicides, disking and the introduction of a new grass species.
One study found the following results to control methods:
“Introduced bluestems can be killed by plowing, applying glyphosate and replanting with native seed. But without follow-up management practices, the nearby introduced bluestem plants repopulated within 1½ years.”
“All treatment combinations temporarily reduced the amount of introduced bluestems, but they typically increased in coverage steadily over the course of a year until it met or substantially surpassed the density before treatment or until dry conditions decreased total plant material.”
Trying to control the grass can be a hard-fought battle, but careful and continual management practices will help. Prevention might be key for growers to keep the grass out. Keeping an eye on your pasture’s grasses is key if you have a small area of growth. Additional prevention measures include spot spraying areas with glyphosate, washing haying or tractor equipment, and maintaining buffers along fence lines.
Many bluestems, including KR bluestem, love soil disturbance. Plowing or disking might temporarily take out the grass, but within a year or two, you will have regrowth if no other management practices are used. If you try to control KR bluestem, plan for a multi-year approach.
ZACH DAVIS is the agriculture and natural resources extension agent with Texas A&M AgriLife Extension. He can be reached at 940-349-2889 or via email at email@example.com.