A brief overview of the biological control of saltcedar

Authors: Carruthers, Raymond; Herr, John; KNIGHT, JEFF - NEVADA DEPT. OF AGRIC.; Deloach Jr, Culver

Submitted to: Proceedings of the California Conference on Biological Control
Publication Type: Proceedings
Publication Acceptance Date: 2/15/2007
Publication Date: 3/30/2007
Citation: Carruthers, R.I., Herr, J.C., Knight, J., Deloach, C.J. 2007. A brief overview of the biological control of saltcedar. In: Hoddle, M., Johnson, M., editors. Proceeding of Fifth California Conference on Biological Control, University of California, 2006, Riverside, California p. 71-77.

Interpretive Summary: Saltcedar is an invasive riparian bush to small tree that infests many waterways throughout the Western United States. USDA-ARS scientists in cooperation with many cooperators have successfully used biological control to manage this weedy plant at many locations is several states from Texas in the south, Montana in the north, from eastern Colorado in the east and along the Pacific Coast in California. Our most successful efforts were implemented in Nevada and Utah where a leaf beetle from China has highly defoliated thousands of acres of invasive saltcedar at multiple locations, and since 2001 has begun causing heavy saltcedar mortality through repeated defoliations. The program has been so successful that several state and federal agencies now are redistributing these beneficial insects across wide areas where control seems a very likely possibility at extremely low cost. This biological control project is not only cost effective but also environmentally sound as it is only known to attack the target plant under field conditions and in areas where native plants were available, these beneficial species are now positively rebounding. Difficulties have arisen in more southern areas of the US where the beetles from China did not seem to work well. However, these problems have now been overcome by importing and safety testing similar beetles from Greece that are better adapted to warm conditions. These beetles are now well established in California and Texas and are beginning to cause heavy defoliation to saltcedar in these locations. We believe that this biological control project will be highly successful across the full range of the saltcedar infestation and save agricultral producers, wildlife managers and thus US taxpayer millions of dollars in control cost and many more benefits that are derived from controlling this invasive pest plant.

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.