Saltcedar Areawide Pest Management in the Western United States

Authors: Carruthers, Raymond; Deloach Jr, Culver; Herr, John; Anderson, Gerald; KNUTSON, ALLEN - TEXAS A & M UNIVERSITY

Submitted to: CABI(Council of Applied Biology International, Oxford, United Kingdom
Publication Type: Book / Chapter
Publication Acceptance Date: 11/1/2007
Publication Date: 4/15/2008
Citation: Carruthers, R.I., Deloach, C.J., Herr, J.C., Anderson, G.L., Knutson, A.E. 2008. Saltcedar Areawide Pest Management in the Western United States. In: Koul, O., Cuperus, G., Elliott, N., Editors. Areawide Pest Management: Theory and Implementation. Wallingford, UK; Cambridge, MA: CABI. p. 271-299.

Interpretive Summary: Saltcedar is a highly invasive and destructive shrub to small tree that was introduced into the US from Europe and Asia. It causes damage to large areas of the western US by destroying native ecosystems, inducing fire and using excessive amounts of water. At the request of many land and water agencies and several farm and environmental groups, USDA implemented a biological control project to aid in its management. This manuscript provides a comprehensive overview of the 15 year project and its results in damage to this pest in over 15 western states. The project has been highly successful and now is producing areas all across the west where saltcedar is on the decline. Beneficial insects from China, Kazakhstan and Greece were first safety tested, approved for field release by authorized state and federal agencies, and then released into the open environment. The beetle now has established, reproduced effectively and spread widely producing lost cost control of saltcedar. All aspects of this project have been summarized in this manuscript providing a complete overview of this effort.

Technical Abstract: Saltcedar (Tamarix spp.) is a group of exotic shrubs to small trees, that have invaded many riparian areas across western North America. Ten species of saltcedars have been introduced into the United States primarily from their countries of origin across Europe and Central Asia. Introduction of saltcedars began in the early to mid-1800's (first noted in 1823) when these species were used extensively for wind and water erosion control along railroads and waterways. In many areas where they were planted, saltcedars naturalized, became well established and spread throughout riparian areas of the west. It is now estimated to infest more than 800,000 hectares (ha) of highly valued riparian land. Saltcedars are deep-rooted, facultative phreatophytes that can use ground water, soil moisture or surface waters. Thus once established, they can occupy areas further from the stream banks and may consume more water across a floodplain than shallow-rooted native phreatophytes. Saltcedars further have the advantage of being facultative halophytes that can use saline groundwater by excreting excess salts through leaf glands. This excretion results in increased salt levels in adjacent soils that may be highly limiting for other less salt-tolerant plant species. The resulting high soil salinity inhibits many native competitors and often leads to extensive monocultures of saltcedar. Saltcedars are also tolerant of fire, drought, inundation, livestock or wildlife browsing (although herbivory is quite limited in North America) and thus have reproduced and spread widely with few natural controls. North American native insects and other wildlife did not evolve with saltcedar and thus rarely use it as a food resource. Since native insects do not feed on the vegetation, roots, boles, flowers or seeds of saltcedar, they exert no noticeable level of natural control. Saltcedars are further tolerant to mechanical damage, and readily resprout from underground lateral buds after heavy scouring or other above ground physical injury. The lack of herbivory coupled with saltcedar's innate ability to withstand adversity and regrow under harsh conditions, has further led to its high densities and an expanding range over the past several decades. This paper describes a highly successful classical biological control program for saltcedar and presents summary data from its control in 15 western states. Biological control insects from Europe and Asia, specifically a leaf beetle (Diorhabda elongata), were used for its control which now covers 100s of thousands of acres. The program is described in detail including cooperative linkages between USDA-ARS and many other cooperating organizations.