How often have you mowed your lawn over the weekend only to find tall weeds growing up to your knees seemingly overnight? You could be dealing with fast-growing King Ranch (KR) Bluestem, an invasive bunchgrass known to grow as much as two to three feet in a week. The City of Denton Parks and Recreation Department is responsible for mowing not only city parks, but also all city properties, rights-of-way, and medians across the entire city. We also deal with KR-related frustration! This article explains what KR Bluestem is, how it was introduced to North Texas, its negative ecological impact, and the very real challenges individuals (and Parks Departments!) face trying to manage the growth of KR Bluestem.
Lawn Mowing and KR Bluestem
Parks and Recreation maintain a regular mowing schedule for parks, city properties, and rights-of-way/medians. Unfortunately, our rigorous mowing schedule cannot keep up with a grass-like KR Bluestem which has the ability to grow as much as three feet in seven to ten days. This means that even mowing on a weekly basis will not entirely diminish the presence of new KR Bluestem growth. Unfortunately mowing more often than once a week is both financially and logistically unfeasible.
What does KR Bluestem look like and where did it come from?
KR Bluestem (or if you want to be technical, Bothriochloa ischaemum var. songarica) is a bunchgrass, a grass that grows in clumps, that can reach heights of one to four feet and is characterized by stems that end in a starburst of purple-tinted seed heads (see image at left). Although KR Bluestem is a bunchgrass, it is the specific characteristics of the grass – its dense growth, large quantities of seeds, and the ease with which it expands over new territories – that make it an invasive species. Not all bunchgrasses are invasive species. In fact, Texas is home to over two-dozen species of native bunchgrasses.
The history of King Ranch Bluestem is a global one. Most experts agree that King Ranch Bluestem originated in the steppe climates of Asia and Europe, with some scientists specifically pointing to China as a point of origin for this specific grass. The grass was purposefully introduced into Texas by ranchers who were looking for a livestock grass that would have an extended growing season, remain drought-resistant, and support larger herds.
Even with its exotic origins deep in the Eurasian steppe, there is also a distinctly Texan connection in King Ranch Bluestem’s history. King Ranch Bluestem gets its name from its introduction as a pasture grass at King Ranch in 1938 by Nico Diaz, a staff agronomist at the ranch. Once introduced to the Texas landscape, King Ranch Bluestem took hold and expanded rapidly, and now it is found in counties in all four corners of the State.
Why is KR Bluestem a problem?
The establishment of KR Bluestem in Texas proved wildly successful. It was widely implemented as a pasture grass as well as an anti-erosion measure in rights-of-ways. The grass successfully prevented erosion in most applications, but as a livestock feed, KR Bluestem failed to provide adequate nutrition for livestock. In fact, most livestock preferred other grazing grasses to KR Bluestem. As an unintended consequence, livestock often depleted a pasture’s native grasses leaving more space for KR Bluestem to establish itself in monocultures: large and dense areas that have limited diversity and often feature only one dominant plant. Monocultures, by their very nature, restrict opportunities for native species to flourish. Agricultural scientists have determined that monocultures of KR Bluestem crowd out other native prairie grasses and support a diminished local ecology with far less diversity in native bird and rodent species.
What are the options for managing KR Bluestem?
KR Bluestem is a difficult grass to manage because it grows at an incredible rate – as much as two to three feet in as little as seven or ten days. Even mowing on a weekly basis will not entirely diminish new KR Bluestem growth. In fact, of the five major interventions for handling invasive agriculture – mowing, plowing, discing (similar to plowing but more mechanically demanding), grazing, and setting it on fire (seriously) – none adequately manages the perpetuation of KR Bluestem. Mowing is inadequate because it is difficult to match the grass’s growth interval and mowing too often only encourages the entrenchment of bluestem monocultures. Plowing and discing both require the removal of surface grass or lawn – a pretty severe intervention. Discing appears to work somewhat on dry soils but only when the process is used repeatedly. Plowing may bury some Bluestem seeds deeper in the soil, but it does not work when conducted as a single treatment because of the resilience and sheer quantity of KR Bluestems’ seeds.
Using livestock herds to graze away KR Bluestem is difficult to do because, as we indicated above, cattle and other grazing livestock prefer tastier grasses. If too large a herd is used the result will be overgrazing of native grasses and more KR Bluestem monocultures. Finally, giving up and setting it all on fire also doesn’t work, because fire can spread KR Bluestem and only proves, at best, a temporary solution. Additionally, implementing a controlled burn for KR Bluestem is difficult to do in certain contexts, such as parks and cemeteries.
Most landscaping and pasture management experts suggest that the best alternative may be passive management: learning to live with KR Bluestem and limiting any actions that might encourage the spread of the grass into areas that are currently unaffected. The City of Denton Parks Department will continue to mow parks properties, city facilities, cemeteries, and rights-of-way on a regular interval to minimize the aesthetic impact of KR Bluestem.
Additional Reading:
“King Ranch Bluestem,” from Texas Invasive Species Institute
http://www.tsusinvasives.org/home/database/bothriochloa-ischaemum-var-songarica
“Introduced Bluestem Grasses: Management on Native Lands,” M. K. Clayton, et. al.,
https://southtexasrangelands.tamu.edu/files/2011/11/ERM036-Introduced-Bluestem-Grasses.pdf
“Red-Streaked Leafhopper and King Ranch Bluestem: Evaluating the Relationship Between Two Invasives”
https://earthzine.org/red-streaked-leafhopper-and-king-ranch-bluestem-evaluating-the-relationship-between-two-invasives/