Ask Mr. Smarty Plants

How to control or eliminate the invasive, non-native, King Ranch (KR) Bluestem (Bothriochloa ischaemum var. songarica) is a question that has been asked many times.  Some questions are from people wanting to get it out of their non-native St. Augustine (Stenotaphrum secundatum) grass lawn and some wishing to control it on a large scale in their grass pastures many of which are non-native Coastal Bermuda (Cynodon dactylon).  There is no quick and easy way to do it.  (By the way, despite its nutritional benefits to cattle, bermudagrass is also considered invasive.)  You can read the answer to a previous general question about controlling it on a large scale in pastures.  Some of the references listed in the previous question are no longer available online.  However, there are other references that you can find.  You can read a study from Texas Wildlife about controlling KR bluestem and other exotic grasses in South Texas.

Let's consider the different options:

Herbicide:

 The paper by Gerald W. Hobson, Tools for Managing Yucca, Sandbur and KR Bluestem in Native and Introduced Range and Pastures, suggests that the nicosulfuron herbicide used "has proven effective with sequential applications to manage or suppress K. R. bluestem in bermudagrass pastures."  The Bayer documentation for this herbicide does not list KR bluestem as a target species, but the Whitney Consulting Group in Georgetown, Texas has published an assessment of its effectiveness against KR. Although this herbicide is recommended for bermudagrass pastures, some varieties of bermudagrass are susceptible to the herbicide according to the Bayer brochure.

Disking or disking + herbicide:

In their paper Evaluation of Herbicide and Disking to Control Invasive Bluestems in a South Texas Coastal Prairie, (Rangeland Economy and Management 65(3):277-285. 2012), Marvin Ruffner and Thomas Barnes found that herbicide alone and herbicide followed by disking were ineffective in reducing the KR bluestem cover.  Disking followed by herbicide did have some effect in reducing KR bluestem.  (The herbicides used were glyphosate, imazapyr and imazapyr + glyphosate.)  Since after treatment the KR bluestem cover eventually returned to pre-treatment levels, they determined that follow-up treatments would be necessary.

Controlled burn:

The late Mark Simmons of the Lady Bird Johnson Wildflower Center and others reported in Selective and Non-Selective Control of Invasive Plants: The Short-Term Effects of Growing-Season Prescribed Fire, Herbicide, and Mowing in Two Texas Prairies [Restoration Ecology 15(4):662-669 Dec. 2007] that prescribed burns during the growing season (summer) were "effective at reducing the abundance of B. ischaemum" while dormant season (winter) burns encouraged KR growth.  Also, the advantage of growing season prescribed fire over tilling/herbicide is that many native grasses can tolerate fire, hence this technique is selective rather than wholesale.  The University of Florida IFAS Extension reports that "Winter Burns Benefit Bermudagrass Hay Fields" with the exception of some varieties such as "Tifton 85, Tifton 78, and Coastcross, may be damaged by fire, especially a backfire, so it may be safest not to burn these particular varieties of bermudagrass. Most other varieties including Coastal, Alicia, Russell and others seem to tolerate fire very well."

How will these control methods affect your coastal bermudagrass and your decision to employ the method?

• Herbicide—The limited information about how the nicosulfuron herbicide will affect various varieties of bermudagrass is a factor to consider.  Cost may also be an important consideration, especially if several applications are necessary.
• Disking + Herbicide—Disking alone does not seem to be effective against KR bluestem, but disking your coastal bermuda will probably require that you reseed after disking whether you use herbicide or not.
• Controlled burn—Coastal bermuda seems to tolerate fire and should regrow after a burn.

Finally, studies by Bob Harms, Competition between KR Bluestem (Bothriochloa ischaemum var. songarica) and Little Bluestem (Schizachyrium scoparium) and Thirty years of King Ranch Bluestem (Bothriochloa ischaemum var. songarica) in N. Hays County, suggest that the native grasses—in particular, Schizachyrium scoparium (Little bluestem)—can out-compete KR bluestem.  This, of course, is not a quick fix, but you can, perhaps, consider sowing native grasses that have good nutritional value for cattle along with your coastal bermuda.  Here are links to reports of the nutritional value of several native grasses:

• Schizachyrium scoparium (Little bluestem)
• Sorghastrum nutans (Yellow Indian grass)
• Andropogon gerardii (Big bluestem)
• Bouteloua curtipendula (Sideoats grama)
• Bouteloua gracilis (Blue grama)