King Ranch (or KR) Bluestem is a perennial grassy weed and its presence in Abilene has been confirmed by theTexas AgriLife Extension Service of Taylor County; there is currently no chemical labeled for its control. Please read below for more information on this invasive weed.
King Ranch (or KR) Bluestem (Bothriochloa ischaemum var. songarica), introduced from Europe and Asia, has greatly increased its range by cultivation for livestock forage and as an inclusion in seed mixes used to stabilize roadsides by highway departments. When it was introduced in the 1920s and 1930s it was seen as a desirable species for erosion control since it is drought resistant and quickly establishes itself. It is now considered invasive and its presence threatens the abundance and diversity of native species. You are well advised and should be congratulated for attempting to control it.
Simply mowing it is not going to get rid of it, however. It will, of course, curb the spread somewhat if the mowing is done before it flowers and sets seed; however, keeping it mowed short is likely to extend its spread by sending out stolons.
The recent 2007 Texas Invasive Plant Conference had a special one day symposium devoted to the discussion of Old World Bluestems and the problems concerning their effective control. You can read abstracts of papers presented there and find that there is no single, surefire method for control of KR bluestem. The methods under investigation are:
1) Herbicides alone—The conclusion of several of the papers is that herbicides alone are not an effective control for KR bluestem.
2) Tilling (disking or harrowing) alone—Here is the recommendation from the Native Prairies Association of Texas in their article, "Want to Plant a Prairie?" by Lee Stone and Arnold Davis
"You've got K-R Bluestem? Plow deeply enough to turn the roots up in the early summer. Do everything you can in the early summer to kill those roots. If you get fall germination of K-R, till your land two inches deep. Don't ever go below this two inch depth. If you go more deeply, you'll just be bringing up more seed. The minute you see any germination at all, use a spring tooth harrow or a section harrow, but never below two inches.
Bank on at least one more germination occurring. Get them too. You won't be planting your prairie until May. But live with that fact. Get the seed to germinate, then kill them with tillage or herbicide. This exotic seeds well, is aggressive, and spreads under conditions of grazing and mowing."
Another study, KR Bluestem Management in Bermudagrass Pastures by Paul Baumann and Ron Leps from the Williamson County Texas Cooperative Extension Service concluded that "What is evident from these
studies is that tillage has a significant impact on KR Bluestem." Their study shows tilling alone is more effective than any of the herbicides alone or herbicides in combination with tilling.
3) Tilling in conjunction with herbicides—One of the papers delivered (Restoration of Native Subtropical Forest in Abandoned Cropland Dominated by Kleberg Bluestem in Cameron County, Texas by Chris Best and Mick Castillo of U. S. Fish and Wildlife Service) reported that "the most effective treatment has been disking followed by 1 year of glyphosate treatment."
Another study, Invasive Ecology of Old World Bluestems and Insights for Management by Marvin Ruffner and Lynn Drawe agreed that "Disking followed by herbicide treatments provided the most effective long-term control of Old World bluestems."
4) Prescribed burns—Mark Simmons of the Lady Bird Johnson Wildflower Center reported in Selective and Non-Selective Control of King Ranch Bluestem: The Short-Term Effects of Growing-Season Prescribed Fire, Herbicide, and Mowing in Texas Prairie 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.
So---given the fact that it isn't practical to pull or dig up all the clumps of KR on your 1/2 acre (that would be the MOST effective way of getting rid of it), the least expensive and most environmental friendly option would be tilling up the roots and/or a prescribed burn during the summer growing season. This may take multiple tillings and you will need to be vigilant for new germination.
from Ask Mr. Smarty Plants, a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.