Great Plains yucca is a native species that competes with forage plants for space and water and at high densities may warrant control. The objective of this study was to determine the efficacy of seven herbicides applied in the spring or fall for Great Plains yucca control. Six foliar herbicides applied by ground application at 187 L ha-1 spray volume, one herbicide applied to individual plant whorls, and a nontreated check were established in June and September of 2009 and 2011. Percent mortality was determined 12 to 16 mo after herbicide application. Most herbicides gave similar control between the 2 yr, with triclopyr in diesel applied to individual plant whorls at 10 g L-1 providing the greatest control at 83%. Most herbicides applied in June near the blooming stage of Great Plains yucca were more effective than September treatments. June treatments providing the greatest reduction in yucca densities were metsulfuron + dicamba + 2,4-D amine + 2,4-D low volatile ester (LVE) at 21 + 113 + 325 + 431 g ae ha-1, metsulfuron + aminopyralid + triclopyr at 49 + 9 + 227 g ha-1, metsulfuron + chlorsulfuron + 2,4-D LVE at 34 + 11 + 431 g ha-1, and metsulfuron + aminopyralid + 2,4-D LVE at 49 + 9 + 431 g ha-1. A single application of a foliar herbicide provided a maximum of 72% mortality of Great Plains yucca, suggesting that repeat application may be necessary to achieve optimum control.
Nomenclature: 2,4-D; aminopyralid; chlorsulfuron; dicamba; metsulfuron; triclopyr; Great Plains yucca, Yucca glauca Nutt.