Evaluation of herbicides for restoring native grasses in buffelgrass-dominated grasslands

Buffelgrass (Pennisetum ciliare) is an exotic grass that threatens arid and semiarid ecosystems. The objective of this study was to determine effectiveness of several herbicides at reducing competition from buffelgrass to enhance establishment of planted native grasses. In Duval County, Texas, plots were delineated in two experiments in a buffelgrass-dominated pasture and mowed on 2 September 2002. On 18 September 2002 and 7 October 2002, a 41% glyphosate (N-(phosphonomethyl) glycine) herbicide was applied to all plots. A mixture of three native grasses-green sprangletop (Leptochloa dubia), plains bristlegrass (Setaria leucopila), and four-flower trichloris (Chloris pluriflora)-was planted on 8 October 2002. On 9 October 2002, 1.12 and 2.24 kg/ha of a 80% tebuthiuron (N-[5-(1,1-dimethyethyl)-1,3,4-thiadiazol-2-yl]-N,N'-dimethylurea) herbicide was applied preemergence to the first experiment, and all other herbicides were applied postemergence on 27 July 2003 to the second experiment. Percent canopy cover of vegetation was estimated with a 20 x 50-cm sampling frame during April, June, and October 2003 and August 2004. Postemergent herbicides had no significant effect on canopy cover of buffelgrass or planted species (p >= 0.05). Canopy cover of native grasses did not exceed 8% on any treatment or sampling date, and buffelgrass cover returned to pre-treatment conditions in less than 1 year; however, the 2.24 kg/ha rate of tebuthiuron suppressed (p < 0.05) canopy cover of buffelgrass compared with controls and increased (p < 0.05) native grasses almost 2 years past application. Tebuthiuron may have potential value in reducing buffelgrass canopy cover and increasing cover of native grasses, particularly Chloris spp.