ARS | Publication request: Diorhabda elongate and saltcedar control: 10 years later

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: August 4, 2011
Publication Date: February 1, 2012
Citation: Clements, D.D., Harmon, D.N., Young, J.A., Knight, J. 2012. Diorhabda elongate and saltcedar control: 10 years later. In: Proceedings Society for Range Management, January 29-February 3, 2012, Spokane, Washington. 65:24.

Technical Abstract: Saltcedar (Tamarix ramosissima), native to Central Asia, is a shrub or small tree that has invaded more than 1.9 million hectares of habitat in southwestern and western United States. Saltcedar was brought to the United States in the early 1800s as an ornamental and later planted for windbreaks and stream bank stabilization. Saltcedar escaped cultivation and spread in riparian and adjacent communities which negatively affected native plant and animal communities. In an effort to control saltcedar, the USDA-Agricultural Research Service started investigating a number of potential control insects in the 1970’s. Following the identification of the leaf beetle (Diorhabda elongata), USDA was permitted to start field tests on the leaf beetle and the potential control of saltcedar. In 1999 we constructed three biocontrol cages at three separate locations in western Nevada; Lovelock, Stillwater and Walker, Nevada. Following quarantine testing, the leaf beetle was brought to field cages in Nevada as well as five other states for testing in 1999. In 2001 the leaf beetle was released in an effort to biologically control saltcedar. Prior to the release in 2001, we marked 100 saltcedar trees at each of the three release sites to monitor vegetation changes over-time. The leaf beetle did not sufficiently populate at the Stillwater site therefore, Lovelock and Walker sites will be reported on. In the spring (last week in May) of 2001 we marked 100 saltcedar trees at each location and set up permanent quadrats to measure plant morphology [e.g. height, diameter, densitometer conditions (percent), foliage (green, senescing, dead foliage/defoliation, dead wood, regrowth), and flowering status], and beetle presence. Also measured were nearest shrub and the primary vegetation directly under the canopy as well as on the edge of the canopy. These measurements were taken the same time of year (last week in May) from 2001 through 2011. Previous reports suggest that following the release of the leaf beetle defoliation of saltcedar tress is significant and that death of the tree can occur within 3-5 years. After measuring defoliation for a decade, complete defoliation (96-100%) reached a high of 54% in 2004 at the Lovelock site and a high of 18% at the Walker site in 2007. By 2011, complete defoliation was recorded at 41% and 14% for the Lovelock and Walker sites, respectfully. In 2001 the percent vegetation cover directly under the saltcedar tree was 10.51% compared to 13.52% on the trees edge. Saltgrass (Distichlis spicata) and tall whitetop (Lepidium latifolium) were the two major species; saltgrass 47% of the quadrats with an average percent cover of 9.26 beneath the canopy while the trees edge quadrat had a 26% occurrence and 6.42% cover. Tall whitetop was present in 47% of the quadrats beneath the canopy and 38% on the trees edge with an average percent cover of 12.68 and 10.26, respectfully. By 2011 tall whitetop was not present in the quadrats and saltgrass had increased to a presence of 50% beneath the canopy and 54% on the trees edge and an average percent cover of 48.46 and 45.19, respectfully. At the Walker site in 2001, 42% of the quadrats beneath the canopy had vegetation while 65% did on the trees edge. The average percent cover was 2.99 beneath the canopy and 4.5 on the trees edge. Cheatgrass (Bromus tectorum) and Tansy mustard (Descurania piñata) were the most frequently recorded species with cheatgrass occurring in 42% of the quadrats beneath the canopy (percent cover = 7.14) and 65% of the quadrats on the trees edge (percent cover = 6.92). Tansy mustard was present in 19% and 22% of the quadrats, respectfully, with an average percent cover of 1.95 beneath the canopy and 1.55 on the trees edge. By 2011 there had been a significant decrease in vegetation beneath the canopy, 2% presence and 0.01% cover. Yet, on the trees edge even though there was a decrease in the presence of vegetation in the quadrats, 28%, there was an increase in percent cover at 6.85. This was due to an increase in rabbitbrush (Chrysothamnus nauseosus), 0 in 2001 to 12% occurrence in 2011 with an average percent cover of 47.92. The interpretation of a dead saltcedar tree has clouded the reality concerning on-the-ground discussions. A defoliated saltcedar tree that looks gray and dead actually has tremendous potential to re-grow redish colored branches that are followed by leaf development and eventually flowering. Also of concern is even though defoliation is occurring, biomass removal in these dense stands remains a problem. The use of heavy equipment and herbicides are most likely tools that will ultimately be used to control saltcedar.