ARS | Publication request: Diorhabda carinulata and tamarisk control

Submitted to: Western Society of Weed Science
Publication Type: Abstract Only
Publication Acceptance Date: October 27, 2011
Publication Date: March 15, 2012
Citation: Clements, C.D., Harmon, D.N., Young, J.A., Knight, J. 2012. Diorhabda carinulata and tamarisk control [abstract]. Western Society of Weed Science. 64:8.

Technical Abstract: Tamarisk (Tamarix ramosissima) also referred to as salt cedar, 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. Tamarisk was brought to the United States in the early 1800s as an ornamental and later planted for windbreaks and stream bank stabilization. Tamarisk escaped cultivation and spread in riparian and adjacent communities which negatively affected native plant and animal communities. In an effort to control tamarisk, 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 carinulata), formerly Diorhabda elongata, the United States Department of Agriculture was permitted to start field tests on the leaf beetle and the potential control of tamarisk. 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 tamarisk. Prior to the release in 2001, we marked 100 tamarisk trees at three release sites in northwestern Nevada 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 of 2001 we marked 100 tamarisk 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], beetle presence and primary vegetation directly under and at the edge of the canopy. These measurements were taken the last week in May from 2001 through 2011. Previous reports suggest that following the release of the leaf beetle, defoliation of tamarisk trees 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. Saltgrass (Distichlis spicata) increased in density and percent cover from 2001 to 2011 at the Lovelock site, whereas the invasive weed tall whitetop (Lepidium latifolium), which was present in 47% and 38% of the quadrats beneath and at the edge of the canopies in 2001, was not recorded in any quadrats in 2011. The interpretation of a dead tamarisk tree has clouded the reality concerning on-the-ground discussions. A defoliated tamarisk 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 tamarisk.