• Comparison of Herbicides for Reducing Annual Grass Emergence in Two Great Basin Soils

      Hirsch, Merilynn C.; Monaco, Thomas A.; Call, Christopher A.; Ransom, Corey V. (Society for Range Management, 2012-01-01)
      Reducing seed germination and seedling emergence of downy brome (Bromus tectorum L.) improves the success of revegetating degraded shrubland ecosystems. While pre-emergence herbicides can potentially reduce these two processes, their impact on germination and emergence of downy brome and revegetation species in semiarid ecosystems is poorly understood and has not been comprehensively studied in soils with potentially contrasting herbicide bioavailability (i.e., residual plant activity). We designed a greenhouse experiment to evaluate the effects two pre-emergence acetolactate synthase-inhibiting herbicides (rimsulfuron and imazapic) on germination and emergence of downy brome and two revegetation grass species (crested wheatgrass [Agropyron cristatum {L.} Gaertn.] and bottlebrush squirreltail [Elymus elymoides {Raf.} Swezey]) that were grown in representative soils from salt desert and sagebrush shrublands. Pre-emergence herbicides significantly (P<0.05) reduced seedling emergence and biomass production of downy brome and crested wheatgrass and increased mortality more so in sagebrush compared to salt desert soil, suggesting that these common Great Basin soils fundamentally differ in herbicide bioavailability. Also, germination and emergence of the two highly responsive species (crested wheatgrass and downy brome) were clearly more impacted by rimsulfuron than imazapic. We discuss these results in terms of how the specific soil physiochemical properties influence herbicide adsorption and leaching. Our results shed new light on the relative performance of these two promising herbicides and the importance of considering soil properties when applying pre-emergence herbicides to reduce germination and emergence of invasive annual grasses and create suitable seedbed conditions for revegetation./Reduciendo la germinación y emergencia del pasto bromo velludo (Bromus tectorum L.) mejora las practicas de re-vegetación en los ecosistemas de matorral degradados. Mientras que los herbicidas de pre-emergencia puede potencialmente reducir estos dos procesos, sus impactos en germinación y emergencia en pasto bromo velludo y re-vegetación de especies en ecosistemas semiáridos no está bien entendido y no ha habido estudios profundos en suelos con potencial de contrastar la bio-disponibilidad del herbicida por ejemplo en la actividad residual en la planta. Se diseño un experimento en invernadero para evaluar el efecto depre-emergencia de acetolactate inhibidor de herbicida (rimsulfuron e imazapic) en la germinación y emergencia del bromo velludo y dos especies de pasto para re-vegetación (triguillo crestado [Agropyroncristatum {L.} Gaertn.] y escobilla cola de ardilla [Elymuselymoides {Raf.} Swezey]) los cuales fueron sembrados en suelos representativos de desierto salado y matorrales de artemisa. El herbicida de pre-emergencia reduce (P<0.05) significativamente la emergencia de plántulas y producción debió masa de bromo velludo y triguillo crestado y aumenta mas la mortalidad en artemisa comparado con el suelo salino del desierto, sugiriendo que estos suelos típicos del Great Basin difieren bastante en bio-disponibilidad del herbicida. Además, la germinación y emergencia de las dos especies altamente responsables (triguillo crestado y bromo velludo) fue más impactado por el rimsulfuron que el imazapic. Discutimos estos resultados en términos de cómo las propiedades fisicoquímicas del suelo influyen en la absorción del herbicida y escurrimiento. Nuestros resultados ofrecen nuevos senderos con respecto al desempeño de estos dos prometedores herbicidas y la importancia de considerar las propiedades del suelo cuando se vayan a hacer aplicaciones de herbicidas pre-emergentes para reducir la germinación y emergencia de pastos anuales invasores y crear un banco de siembra adecuado para la re-vegetación.
    • Invasion of Broom Snakeweed (Gutierrezia sarothrae) Following Disturbance: Evaluating Change in a State-and-Transition Model

      Thacker, Eric T.; Ralph, Michael H.; Call, Christopher A.; Benson, Brock; Green, Shane (Society for Range Management, 2008-05-01)
      Broom snakeweed (Gutierrezia sarothrae [Pursh] Britt. Rusby) is an aggressive native invasive species that thrives after disturbance in semiarid rangelands of the western United States. A 5-yr (2002-2006) study was initiated following grazing and fire disturbances on an Upland Gravelly Loam ecological site in the sagebrush steppe of northern Utah, to evaluate broom snakeweed invasion in different plant communities. The study site originally had two plant communities: a sagebrush/ bunchgrass community that received alternate-year, fall cattle grazing, and was dominated by bluebunch wheatgrass (Elymus spicatus) and an open stand of Wyoming big sagebrush (Artemisia tridentata subsp. wyomingensis), and a sagebrush community that received continuous, annual, spring cattle grazing that removed the bunchgrasses, leaving a dense stand of Wyoming big sagebrush with an understory of Sandberg bluegrass (Poa secunda). Portions of these two plant communities were burned in a wildfire in 2001, removing the sagebrush, and creating two additional communities. The burned portion of the sagebrush/bunchgrass community became a bluebunch wheatgrass-dominated community, and the burned portion of the sagebrush community became a snakeweed-dominated community. Foliar cover, aboveground biomass, and sagebrush and snakeweed densities were compared among the four communities. Mature snakeweed plants that existed in the sagebrush/bunchgrass community were eliminated in 2003, because of drought conditions. Snakeweed was eliminated in the bluebunch wheatgrass community by the wildfire in 2001, and there was no reestablishment. Snakeweed density and cover remained constant in the sagebrush community. Snakeweed cover increased from 2% to 31% in the snakeweed community, despite the presence of Sandberg bluegrass. The data were used to evaluate and update the current Upland Gravelly Loam (Wyoming big sagebrush) ecological site description in the Great Salt Lake Major Land Resource Area and its state-and-transition model to reflect vegetation changes associated with snakeweed invasion.