Get reliable rangeland science

Woody plant encroachment on rangeland used for beef cattle production and/or wildlife use in the southwestern United States has been a major problem of ranchers for many decades. Aminocyclopyrachlor premixed with triclopyr-amine was first marketed for use on grazing lands in Texas, Oklahoma, New Mexico, and Arizona in 2020. This herbicide was marketed for control of honey mesquite (Prosopis glandulosa) (NRCS 2025), huisache (Vachellia farnesiana a.k.a. Acacia farnesiana), and associated brush species and broadleaf forbs on grazing lands. Long-term (i.e. four to ten years post-application) honey mesquite canopy evaluations in aerial and ground broadcast-applied trials revealed more than twice the treatment life (i.e. the time from treatment until brush canopy returns to an economic threshold) with aminocyclopyrachlor+triclopyr-amine (ACP+T) treated plots versus plots treated with past industry standard s (Medlin et al. 2019). Similar results were obtained for huisache treated plots evaluated four to six years post-application. Recent research has evaluated picloram and/or chlorsulfuron+metsulfuron-methyl combinations applied with ACP+T to widen the spectrum of activity and address additional undesirable species on rangelands while evaluating impacts on desirable plant species. When evaluated 40 months after application, ACP+T (140+280 g ae ha-1) applied alone was highly efficacious (100% mortality) on honey mesquite, moderately efficacious (66% mortality) on guajillo (Acacia berlandieri), and slightly efficacious (less than 25% mortality) on all other woody plant species present. When ACP+T was applied in combination with picloram (560 g ae ha-1) or picloram and chlorsulfuron+metsulfuron-methyl (10.5+33.5 g ai ha-1) mortality of twisted acacia (Vachellia schaffneri a.k.a. Acacia schaffneri) increased to 25% and 50%, respectively. A tank mix of ACP+T (210+420 g ha-1) with chlorsulfuron+metsulfuron-methyl resulted in 100% mortality of honey mesquite, twisted acacia, and whitebrush (Aloysia gratissima), less than 25% mortality of spiny hackberry (Celtis ehrenbergiana), and 0% mortality of ephedra (Ephedra antisyphilitica), guayacan (Guaiacum angustifolium), and lotebush (Ziziphus obtusifolia).