• Economics and Optimal Frequency of Wyoming Big Sagebrush Control With Tebuthiuron

      Torell, L. Allen; McDaniel, Kirk C.; Ochoa, Carlos G. (Society for Range Management, 2005-01-01)
      The optimal frequency of tebuthiuron (N-[5-(dimetylethyl)-1,3,4-thiadiazol-2yl]-N,N9-dimethylurea) treatments was investigated for Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) when added forage for livestock and wildlife are considered to be the economic benefit of the treatment. Data collected at 8 northwest New Mexico study sites were used to define key relationships for the economic analysis. This long-lived sagebrush control practice was found to be a viable investment for landowners who participate in available cost-share programs. At productive sites, where average herbaceous production increased to over 700 kg/ha following big sagebrush control, the economic value of added forage justified the total cost of the herbicide treatment. Tebuthiuron rates higher than 0.5 kg active ingredient/ha lengthened the expected life of the brush control treatment, but the extended life did not justify the added cost. The threshold abundance of sagebrush needed for economical control was found to be variable, depending on treatment cost, study site, and the economic value of forage. With a 50:50 cost-share arrangement and with forage valued at 7/AUM, the economic sagebrush canopy threshold from the livestock grazing perspective was estimated to range between 6% and 14%, depending on site productivity. A second brush control treatment would optimally be implemented before forage production was fully depleted by the recovering brush canopy. Because some native fauna are closely tied to big sagebrush plant communities and benefit from the shrubs’ presence, the trade-off in the desired abundance of big sagebrush must be weighed between economic considerations and other resource values of interest.  
    • Wyoming Big Sagebrush Recovery and Understory Response With Tebuthiuron Control

      McDaniel, Kirk C.; Torell, L. Allen; Ochoa, Carlos G. (Society for Range Management, 2005-01-01)
      Field data collected over a 20-year period at 8 sites in northwestern New Mexico was used to determine Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle and Young) recovery following control with tebuthiuron (N-[5-(1,1- dimethylethyl)-1,3,4-thiadiazol-2-yl]-N-N9-dimethylurea) and to relate understory perennial grass yield to overstory canopy cover. Tebuthiuron killed between 80% and 95% of mature Wyoming big sagebrush plants within 18 months of chemical treatment, but through recruitment plant numbers equaled or exceeded pretreatment density (plants/m2) at 3 of the 8 sites and were increasing at other locations near the study’s end. Wyoming big sagebrush canopy cover averaged <2% the first 10 years after herbicide treatment but had returned to near pretreatment levels (>15%) at 2 sites, to between 5% and 10% at 4 sites, and to less than 3% at the remaining 2 sites. Treatment life was projected to exceed 35 years for 6 of the 8 study sites. Higher rates of tebuthiuron generally extended treatment life. Annual average perennial grass yield increased on treated areas relative to untreated rangeland at all study sites over the 20-year study period. Grass yield was highly variable between years, with pronounced increases when weather and environmental conditions were favorable for grass growth. A nonlinear S-shaped curve best described overstory-understory relationships and also defined the time path of Wyoming big sagebrush recovery, which differed by study site.