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, saltcedar leaf beetles were collected and released for biological control of saltcedar at five sites in north central Texas during June-August, 2010. A total of 81,000 beetles were field collected near Big Spring, TX, transported and released at the five sites. During surveys in October, beetles were abundant and had increased to numbers sufficient to defoliate saltcedar trees at two sites. At the remaining three sites, only a few beetles were present and no tree defoliation had occurred. The lack of high beetle populations at the collection site near Big Spring, TX limited the number of beetles available for release in 2010. Additional beetles will be released at these sites in 2011. Vegetation survey plots were established at two sites to document changes in vegetation as saltcedar declines. Baseline data were collected in October on percent cover, species composition and density and will be collected again in 2011 to monitor vegetation changes.
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. The release site is treated with ant bait to temporarily suppress ants which feed on beetle pupae. Several releases of 15,000-20,000 beetles per release are made during June-August to establish a populations. 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, recovery of grasses and forbs requires 2-3 years. For this reason, two sites where beetles are already established and defoliating trees were selected as changes in vegetation should become evident within the project period.
Beetle Collection, Release and Impact. A total of 81,000 saltcedar leaf beetles were collected from saltcedar trees in the vicinity of Big Spring, TX. Beetles were held in paper bags overnight in a refrigerator and then packaged in coolers and shipped via overnight express to NRCS offices. NRCS personnel released the beetles onto saltcedar trees at each of the five release sites. In October, beetle abundance and tree defoliation by beetles was measured at each site. Ten saltcedar trees spaced about 30 meters apart were numbered and tagged along a transect extending from the release site, with the release trees at the center. Each sample tree was visually searched for 4 minutes and the number of adults and larvae was recorded. The percent of the tree canopy consisting of branches with green foliage, with branches defoliated by saltcedar leaf beetles, and with dead branches was then visually estimated and recorded.
In general, saltcedar beetle populations at Big Spring and surrounding counties did not increase or disperse in 2010 as rapidly as they did in 2009. One explanation is a large proportion of the beetle population, as pupae, may have drown as a result of the heavy and prolonged rainfall that occurred in late June and early July across much of west Texas. The pupal stage occurs on the soil surface for about 5-6 days before the adult beetle emerges. Pupae are therefore susceptible to drowning when low lying areas flood and streams and rivers overflow. Remnants of Hurricane Alex, downgraded as a tropical storm, brought heavy rainfall into the West Texas area in beginning in late June. From June 29 through July 9, rainfall occurred on 8 of these 11 days at Big Spring, TX and totaled 3.34 inches. If a large portion of the beetle population was in the pupal stage at this time, which is likely, these pupae could have drown during this period of rainfall. As saltcedar and therefore beetles occur in areas prone to flooding, this unusual rainfall event may have resulted in an overall decline in beetle populations at many sites. Also, the lack of high beetle populations at the collection site near Big Spring limited the number of beetles available for release in 2010.
Vegetation Monitoring and Impact of Beetles. The vegetation at two sites was characterized by recording the percent cover, species composition and density in four plots. Each plot was 20 m long. Percent cover of each plant species was measured along a 20 m tape stretched along each plot for each of three layers: herbaceous layer 0-0.5 m., shrub layer 0.5-2.0 m and tree layer > 2.0 m. A belt transect was then made to determine species composition and plant density in each of 20 two meter squared sub plots along the 20 m tape. In each plot, the percent of ground cover within the plot occupied by each plant species, bare ground or ground covered by dead plant material was recorded. To measure impact of beetle feeding, ten representative saltcedar trees were selected along the 20 m belt transect for each plot. For each marked tree, the percent of the total canopy that has green foliage, that was defoliated by beetles, and that was dead was recorded.
Impacts and Contributions/Outcomes
Presentations on saltcedar biological control were made at seven conferences, workshops and meetings and attended by 465 participants, of which an estimated 290 were ranchers, farmers and landowners. Two field tours of sites where saltcedar beetles were present were held during the year and attended by about 33 participants.
NRCS Area RC&D
PO Box 1114
Sweetwater, TX 79556-1114
Office Phone: 3252354300