Response of Range Vegetation to Grid Placement and Aerial Application of Karbutilate

Abstract

Karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxypheny)-1, 1-dimethylurea], formulated as a ball 1.34 cm in diameter, was applied to brush-infested rangeland with fixed-wing aircraft and in a grid pattern by hand at an average density of four balls/12.4 m2 (1.83-m spacing). Control of woody plants with karbutilate applied by hand in an exact grid pattern was not different from aerial applications at the same rate. Based on evaluations at least 24 months after application, karbutilate at 0.56 or 1.12 kg/ha did not control honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell] in the subhumid Post Oak Savannah or semiarid Rolling Plains of Texas. At 2.24 kg/ha, canopy reduction of honey mesquite averaged 70% with 20 to 25% of the population killed. Post oak (Quercus stellata Wangenh.), blackjack oak (Quercus marilandica Muenchh.), yaupon (Ilex vomitoria Ait.), or winged elm (Ulmus alata Michx.) in Post Oak Savannah were not killed by 2.24 kg/ha. Karbutilate eliminated all vegetation in a 25 to 45-cm diameter circle, depending on concentration of active ingredient in the ball, the year of treatment regardless of vegetation region. The bare areas were revegetated within 2 yr following application in the Post Oak Savannah. However, bare areas in sodgrasses, primarily tobosa [Hilaria mutica (Buckl.) Benth.] and buffalograss [Buchloe dactyloides (Nutt.) Engelm.], where 1.12 and 2.24 kg/ha were applied averaged 20 to 30 in diameter, respectively, 32 months after application to sandy clay loam in the Rolling Plains.