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. In cooperation with local ranchers and NRCS personnel, about 80,000 saltcedar leaf beetles were collected and released for biological control of saltcedar at five sites in north central Texas in 2010. During surveys in October, 2010, beetles were abundant and had increased to numbers sufficient to defoliate saltcedar trees at two sites. This initial success was stymied by record-setting cold weather in early February, 2011, which apparently killed leaf beetles at these and other sites and as a result no beetles could be found in 2011 at four of the five sites. There was no source of beetles to collect and re-establish these populations in 2011. Also, due to the record-breaking drought in 2011, there was little plant growth observed in the vegetation study sites. Due to these weather extremes, a one-year no-cost extension was requested and approved to allow this work to continue in 2012. An extension publication titled “Biological Control of Saltcedar” was written by Knutson et al. and published by Texas AgriLife Extension Service and two issue of the Beetle-Mania newsletter were written and distributed to about 125 land owners and land managers.
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 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. In late 2010, leaf beetle populations were established at the release sites in King County on the Wichita River and in Mitchell County on the Colorado River. A survey of the King County site in early October, 2010 found that beetles had defoliated an average of 29% of the canopy of sampled trees and that leaf beetles had dispersed along 0.3 miles of the saltcedar along the Wichita River near the release site. These results suggested the beetle population was well established, dispersing and had increased to numbers sufficient to significantly defoliated saltcedar trees. At the Mitchell County site, leaf beetles had defoliated ca. 45 acres of saltcedar by late fall and were dispersed across an area of about 6 square miles. At the Kent County site, very few beetles were present and no trees were defoliated in October. At the Garza County site, leaf beetles were abundant in October and the average canopy defoliation was 26%, suggesting this population would likely establish and increase in 2011.
Despite this promising results at the close of 2010, a late spring freeze in early February, 2011, apparently killed most of the leaf beetles at these and other sites throughout west Texas. Record-breaking cold swept through west Texas and high temperatures were below freezing for 2-4 consecutive days as far south at the Pecos River. Surveys of these five sites in the summer of 2011 found no beetles at any site. Late in the summer, the owner of the site in Mitchell County found a remnant population of beetles that later increased. It is possible that some beetles also survived at the King County site but went undetected. The large leaf beetle population at Howard County was also lost so there was no source of beetles from which to collect and release beetles again at the project sites during 2011. If the source populations recover in 2012, beetles could be collected and released again at these sites.
Vegetation Monitoring and Impact of Beetles. The vegetation study at King County was discontinued following the loss of the beetle population there. The vegetation study at Mitchell County was sampled in 2011 but due to the record-breaking drought in 2011, very little plant growth was recorded in the study plots. If rainfall returns, this study will be continued in 2012 since the leaf beetle population recovered late in 2011.
Impacts and Contributions/Outcomes
Educational Resources. An extension publication titled “Biological Control of Saltcedar” was written by Knutson et al. and published by Texas AgriLife Extension Service. This five page bulletin is available on-line at https://agrilifebookstore.org/. This bulletin was distributed at Extension educational programs dealing with brush control and invasive species. Outcomes of this project were also reported by Knutson at the Texas Invasive Plant and Pest Conference and the annual meeting of the Saltcedar Biological Control Consortium. A spring and summer issues of the Beetle-Mania newsletter on biological control of saltcedar were written and distributed to about 125 land owners and land managers and posted on the website: http://bc4weeds.tamu.edu.
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