An Overview of the Biological Control of Saltcedar

Authors: Carruthers, Raymond; Herr, John; Deloach Jr, Culver

Submitted to: Weed Science Society of California Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2007
Publication Date: 5/30/2007
Citation: Carruthers, R.I., Herr, J.C., Deloach, C.J. 2007. An Overview of the Biological Control of Saltcedar. Proceedings of California Weed Science Society. 59:128-134/

Interpretive Summary: Saltcedar in a highly invasive shrub that originally was imported from Eurasia to provide erosion control along railroad and streams during the mid-late 1800s. It naturalized and has expanded its range from Northern Mexico to the Canadian border and from the Pacific Coast to the Mississippi River. In these areas it causes extensive damage to agriculture and the natural environment through extensive water use, salinization of soils, and by increasing wildfire frequency. Additional negative impacts reduce rangeland and riparian area productivity, impact grazing potential and thus cause significant economic loss to rangers and other land and waterway managers. I leaf beetles from China and Greece have been successfully used in a Classical Biological Control project to severely defoliate saltcedar and thus provide increasing levels of control in many western states. The leaf beetle was shown to be safe and effective in 15 test sites in 6 western states and has spread effectively to many adjacent areas through USDA implementation efforts. Currently, thousands of acres of saltcedar have been defoliated by this beneficial insect and many more areas will soon be treated using this control insects. This project is expected to save US rancher and the general public many millions of dollars in losses caused by saltcedar and additional saving in pesticide costs that now will not have to be spent.

Technical Abstract: Saltcedar (Tamarix spp.) is a major invasive weed found throughout the Western United States and Mexico. Introduced into North America in the 1800s, this shrub, to small tree, now infests many riparian areas where it displaces native vegetation, increases fire hazards, uses extensive amounts of water, increases flooding during high water events and thus has caused extensive damage to agricultural and natural ecosystems. In 2001, scientists from the United States Department of Agriculture (USDA), Agricultural Research Service (ARS)and cooperators from many other institutions, released a leaf beetle (Diorhabda elongata) from Eurasia into test areas in several states to initiate and evaluate a new biological control program for saltcedar. This leaf beetle established well in most northern sites and has spread rapidly causing extensive defoliation of saltcedar in many release areas. A combination of ground-based monitoring and remote sensing has been used to monitor and document beneficial impacts caused by this biological control program, showing 1000s of acres of defoliated saltcedar and increasing tree mortality through time at various test sites. This program has now been expanded into an implementation phase by USDA-APHIS and others, operating in at least 14 states north of the 38 parallel in the western U.S. Introduction and establishment of these and similar leaf beetles into more southern areas of the western U.S. has proven more difficult both in terms of establishment success, and in documenting and assuring the safety of a wider range of beetle bio-types or species, in respect to feeding on native Frankenia spp. Though a series of laboratory and field cage studies, and open field tests we believe that beetles from Crete, Greece may be suited for release into Southern California (release permits pending) as this beetle is now causing heavy levels of saltcedar defoliation in a test sites in Texas where it was released by USDA-ARS in late 2003. Field releases were initially made at this location as there was no potential jeopardy to Frankenia salina as it is not native in that area. Test sites in Texas were then used to gain further open field host specificity test data on the Crete, Greece beetle preference for ovipositional selection of saltcedar over planted Frankenia. The results of these tests suggest that minimal,but some risk, may be involved in using Greek D. elongata for control of saltcedar in Southern California. Other similar leaf beetles have not yet been tested at this level of detail and thus research is continuing on their efficacy and safety though the efforts of USDA-ARS and others in California and adjacent states. This effort was organized in cooperation with the Saltcedar Biological Control Consortium that is made up of over 60 federal, state and private groups all interested in the widespread reduction of saltcedar in the western U.S.