A quick drive down most any South Texas highway will reveal a sea of waving stems from introduced bluestem grasses, namely King Ranch and Kleberg bluestem, which look nearly identical to the naked eye. Once brought over from China and South Africa, these plants were researched and released for commercial production as solutions for soil erosion control and forage grasses for livestock.
Reports have indicated these grasses were not only planted on the sides of the highways, but also along riparian areas and steep slopes. These invasive grasses did not stay in the right-of-way. They have encroached into productive rangelands and pastures and even neighborhood backyards.
The plant characteristics desirable in Texas – hardy, fast to produce seed, establishing quickly from seed, early to green-up, withstanding many environmental conditions, and thriving on a variety of soil types – has now made it difficult to control its aggressive spreading onto land where it’s not welcome.
The biggest downfall to King Ranch bluestem is that it outcompetes other grasses and forbs, creating a monoculture of just that one grass. Wildlife thrive on lands with plant diversity, providing plenty of food to eat and plants for cover throughout the year as each plant species grows, matures and produces seeds at different times. Native plant communities have co-existed for a long time and for the most part maintain a plant balance, whereas a field full of thick King Ranch bluestem provides little for wildlife to eat or even to maneuver through.
From a livestock perspective, some say that “even a poor grass is better than no grass!” Understandably, these introduced bluestems do provide livestock forage, but because of their quick growth and production of stems and seed heads early, they are not palatable for long in the spring. Consequently, livestock will seek out other plants in the pasture before being forced to eat the stemmy King Ranch or Kleberg bluestem.
This increased pressure on more desirable plants leads to overuse, reduction in root growth, and eventual death of the better grazing plants. You guessed it – the bare soil left is quickly overtaken by King Ranch bluestem (remember it was largely avoided by livestock and allowed to contribute new seeds to the soil) and over time the plant community will shift to a monoculture of these invasive grasses. Ranchers have even found hardy forage grasses, such as buffelgrass, to be overtaken by King Ranch bluestem.
In this age of technology and advancement, our first thought might be to “Google” how to control these plants. This should be simple enough, right? Unfortunately, researchers have spent an enormous amount of time trying to manage these invasive grasses and thus far, are best at identifying what not to do to encourage them. King Ranch bluestem thrives on disturbance, which means that shredding/mowing, disking and burning favor their quick growth and spread. Mowing can change the grass’ growth form so that it begins to grow parallel to the ground and seed out at shorter heights. Disking and burning create bare ground, which is quickly recolonized with King Ranch bluestem.
Deep plowing can uproot the grasses and turn the soil over to bury potential new seed, but if not combined with intensive glyphosate applications, reseeding and elimination of King Ranch bluestem on the pasture borders, the invasive grasses can move back in within months, after a high financial expense to the landowner.
Glyphosate (trade name of Roundup
®) has been used at high rates to control these green, growing grasses. Unfortunately, glyphosate will also control most other growing plants as well because it is not selective, and it does not sterilize the King Ranch bluestem seed already added to the soil. Applying glyphosate in combination with plowing or multiple disking events may reduce the amount of King Ranch bluestem, at least short-term.
Before investing in an intensive control and replanting effort, it would be helpful to know how long the King Ranch bluestem seeds waiting in the soil are viable for germination. Texas A&M AgriLife Extension Service has an active King Ranch/Kleberg bluestem research program near Corpus Christi investigating seed germination rates, the rate of glyphosate needed to control established grasses, pre-emergent herbicides that will sterilize the existing seedbank in the soil, and potential grasses for replanting these areas once they are clean.
In the meantime, there are several practices to prevent King Ranch bluestem from becoming established on a property or to reduce spread. As previously mentioned, any type of disturbance, such as disking, mowing or burning, will encourage the spread of these grasses. If a land manager is not prepared to intensively manage the grass, many times they are better off leaving it alone.
Trucks or equipment can bring in these invasive bluestem seeds, so care should be taken to reduce traffic or request a “weed wash” before entering. Monitor land near roads and exterior fences to identify any new King Ranch bluestem recruits and treat immediately, before they become a nuisance.
Without a silver bullet answer for controlling invasive bluestem grasses, landowners should become familiar with how common land management techniques will impact the grass and what active role they can play in reducing their spread. For more information on the history and management of King Ranch and Kleberg bluestem, download “Introduced Bluestem Management” from the SouthTexasRangelands.tamu.edu website under the “Publications” tab.
— by Megan Clayton, Ph.D., associate professor, Texas A&M College of Agriculture and Life Sciences Department of Soil and Crop Sciences, and Texas A&M AgriLife Extension Service range specialist, Corpus Christi