Caucasian old world bluestem (OWB), seeded for conservation and forage production, has escaped into rangelands in the southern and central Great Plains. Glyphosate, imazapic, imazapyr, imazethapyr, and sulfometuron methyl herbicides were applied at the four- to five-leaf stage and again 8 wk later in 2003 and 2005 to control Caucasian OWB. Glyphosate at 1.14 kg ai/ha at each application was the only treatment that reduced frequency and tiller density of Caucasian OWB, and also controlled over 80% of growth, at 6 wk after the first treatment (WAT) both years. After the first autumn frost, plots treated with glyphosate and imazapyr at 0.28 kg ai/ha at each application had lower frequency and much greater suppression of Caucasian OWB growth than plots treated with other herbicides. Tiller densities and seedhead densities were also less in plots treated with glyphosate and imazapyr compared to other herbicides and the nontreated control. Biomass at the end of the season was near zero for plots treated with glyphosate and imazapyr in 2003, and 26 to 46% of the nontreated control biomass in 2005. Frequency of Caucasian OWB the year following treatment was less than 5% for both glyphosate and imazapyr. Broadcast application of glyphosate and imazapyr also controlled remnant native vegetation in plots, thus different application methods, such as ropewick application, may be useful to avoid native grass injury.

Nomenclature: Glyphosate, imazapic, imazapyr, imazethapyr, >sulfometuron methyl, Caucasian old world bluestem, Bothriochloa bladhii Retz (S.T. Blake) BOTBL