BIOLOGICAL CONTROL OF SALTCEDAR ON WEST TEXAS RANCHES CONSERVES FORAGE AND WATER RESOURCES
Saltcedars (Tamarix spp.) are exotic and invasive small trees or shrubs which commonly form dense stands along rivers, streams and riparian areas of west Texas and degrade water and land resources. Little or no forage grass survives beneath these dense stands due to the canopy shading by saltcedar and competition for water. Saltcedar thickets also interfere with gathering cattle. Several species of leaf beetles were introduced into the US for the biological control of saltcedar. These beetles and their larvae consume saltcedar leaves. Defoliated trees transpire less water and allow sunlight to reach the soil, favoring growth of grasses and other plants. In cooperation with local ranchers and NRCS personnel, saltcedar leaf beetles were collected and released for biological control of saltcedar at five sites in north central Texas in 2010-12. In 2012, large populations of beetles defoliated extensive areas of saltcedar trees at three of these locations. Beetles are well established at these sites and are expected to continue to suppress saltcedar growth and naturally disperse. Beetle numbers were low or absent at the two remaining sites. Recovery of forage grasses and other vegetation following slatcedar defoliation was evaluated at one release site. Educational efforts during 2012 included writing two issues of the Beetle-Mania newsletters and co-organizing the annual Saltcedar Biological Control Consortium for Texas, New Mexico and Mexico.
Objective 1. Establish Self-Sustaining Populations of Saltcedar Leaf Beetles.
Release sites are located on properties with large saltcedar infestation and on major river systems in north central Texas. Once beetle populations are established, releases are discontinued and beetles naturally reproduce and disperse throughout the county.
Objective 2. Document Recovery of Grasses and Forbes Following Saltcedar Defoliation.
Once beetles begin to defoliate trees, competition for sunlight and water should be reduced and grasses and forbs should increase beneath the canopy of defoliated saltcedar trees. Vegetation will be sampled along permanent transects to measure this recovery.
Establishing Self-Sustaining Populations of Beetles. Following release efforts in 2009, leaf beetles populations were established at King County and Mitchell County sites in 2010. However, beetle numbers were very low or absent in 2011. This is believed due to very cold weather, a blue northerner, during early February, 2011, that apparently killed most of the overwintering beetles. The winter of 2011-2012 was very mild with no late spring freeze. As a result, beetle populations rapidly recovered during 2012.
At the King County site, all of the saltcedar along about ten river miles was entirely defoliated by leaf beetles by late July. The beetle population at the Mitchell County site also recovered and again defoliated about 45 acres of large saltcedar trees. Many of these trees now have very little green canopy as a result of repeated years of defoliation and grasses and other plants are increasing beneath the saltcedar canopy. Beetles at the Motely County site also increased dramatically and defoliated saltcedar trees along more than 50 miles of the Pease River. The NRCS cooperator reported that ranchers had decided to delay and possibly forgo herbicide spraying for saltcedar due to the impact of the beetles. No beetles were present at the two release sites in Kent and Garza Counties. An additional 17,500 leaf beetles were released at the Garza County site in 2012.
Vegetation Monitoring and Impact of Beetles. A series of plots were established at the Mitchell County site to document recovery of grasses and other vegetation as the saltcedar is defoliated. Due to the record-breaking drought in 2011, very little plant growth has been recorded in the study plots. Vegetation cover and plant species data were collected at this site in 2012 to continue to monitor vegetation changes.
Educational and Outreach Efforts. Spring and summer issues of the Beetle-Mania newsletter on biological control of saltcedar were written and distributed to about 150 land owners and land managers and posted on the website: http://bc4weeds.tamu.edu. I co-organized with Sul Ross University the annual Texas/New Mexico/Mexico Consortium for Biological Control of Saltcedar held in El Paso, TX. About 45 people attended. Represented at the meeting were two international agencies, five federal agencies ARS, NRCS, U.S. Fish and Wildlife Service, National Park Service and Bureau of Reclamation, four Texas state agencies two state universities, and two nonprofit organization The program included presentations by 18 speakers, breakout sessions and reports by four subcommittees (Science, Wildlife/Environment, Federal, State and Private Liaison, and Mexican Cooperative Relations).
Impacts and Contributions/Outcomes
Saltcedar leaf beetle populations are now well established at three of the five ranches and are widely and naturally dispersing to new saltcedar infestations. As beetles repeatedly defoliate saltcedar, the trees dieback, cease flower and seed production, and becomes less competitive, allowing grasses and other vegetation to return. The process requires several years, and beetle populations can be temporarily reduced due to cold winters. Results show that biological control has the potential to provide a very inexpensive, target-specific and sustainable method of suppressing saltcedar infestations on ranches in many regions of west Texas.
NRCS Area RC&D
PO Box 1114
Sweetwater, TX 79556-1114
Office Phone: 3252354300