|Deloach Jr, Culver|
Submitted to: Sustainable Agriculture International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/20/2007
Publication Date: 10/20/2007
Citation: Deloach Jr, C.J., Knutson, A.E., Moran, P.J., Michels, G.J., Thompson, D.C., Carruthers, R.I., Nibling, F., Fain, T.G. Biological Control of Saltcedar (Cedro salado) (Tamarix spp.) in the United States, with Implications for Mexico. 2007. In: Lira-Saldivar, R.H., editor. Bioplaguicidas Y Control Biologico. International Symposium of Sustainable Agriculture, 24-26 October 2007, Saltillo, Coahula, Mexico. p. 142-172.
Interpretive Summary: The invasion of western North American riparian ecosystems by saltcedars (Tamarix spp.) small, deciduous, cold-tolerant trees from central Asia and the Mediterranean area are causing one of the worst ecological disasters in the recorded history of that region. Classical biological control offers good potential for permanent, inexpensive and control that does not harm any plants outside the genus Tamarix using an introduced leaf beetle, Diorhabda spp. from China and Kazakhstan (for northern areas) and from Greece (Texas, New Mexico). However, athel (T. aphylla), large, evergreen, cold intolerant, probably introduced from North Africa, is of moderate value in northern Mexico as shade trees and windbreaks. The beetles damage athel moderately in caged tests but a series of outdoor, uncaged tests in Texas at Big Spring in 2005 and 2006 demonstrated that the Diorhabda females laid only 8-14% of their eggs on athel in side-by-side tests and at Kingsville, TX they never established when released in mixed saltcedar/athel stands or on athel-only roadside stands, all indicating the probability of only small or no damage to athel. In view of these results, a committee of Mexican scientists and officials agreed not to oppose releases along the Rio Grande in Texas upstream form Presidio. Therefore, we released the Crete beetles at 7 sites on 29 June; monitoring during the summer indicated that some sites may become established.
Technical Abstract: The ever increasing invasion by exotic organisms from other continents poses one of the greatest threats to the well-being of North American native ecosystems. Among the worst of these is saltcedar (Tamarix spp.). These are shrubs to small trees introduced from Asia and the Mediterranean area into the western United States from the 1820s as garden ornamentals and to prevent streambank erosion. Their populations exploded after the late 1920s and today they have invaded ca. 800,000 ha of highly valuable riparian areas, and form dense, monotypic thickets form the central Great Plains to the Pacific and from Montana into northern Mexico. These thickets have displaced native plant communities, degraded wildlife habitat (including that of many rare, threatened and endangered species), use large quantities of scarce groundwater, reduce stream flows, enhance wildfires, alter stream channels and reduce recreational values. Classical biological control, is ideally suited to these conditions, and has been much used and proven effective. It has been used against over 135 weeds worldwide since 1865 and against ca. 40 exotic weeds of North America since 1945. USDA-ARS began biological control of saltcedar at Temple, TX in 1986 with risk analyses and explorations for overseas natural enemies. The first of these, a leaf beetle, Diorhabda sp., from NW China and E. Kazakhstan defoliates the trees in both the larval and adult stages and has 2 to 5 generations per year. Intensive testing at Temple, and after 1998 also at Albany, CA, demonstrated that they beetles could feed and complete their life cycle only on saltcedars (mostly Tamarix chinensis and T. ramosissima), much less on athel (T. aphylla) and slightly or none on the 4 native Frankenia spp. tested. They were released at 10 sites in 6 western states in May 2001. They established at 5 of 6 sites in Nevada, Utah, Wyoming and Colorado (all north of the 38th parallel) but not at the 4 sites south of the 38th parallel in Texas and California. By 2007, they had defoliated from 36,000 ha at Lovelock, NV to 3,200 ha at Lovell, WY to 2,000 ha at Schurz, NV and Delta, UT and 162 ha at Pueblo, CO. We discovered a more southern adapted ecotype of D. elongata in Greece, tested it extensively in quarantine, and released it at Big Spring in NW Texas in April 2004. The rate of saltcedar defoliated there is increasing ca. 10 fold per year, and to 10 ha in October 2006. We have redistributed beetles from the Big Spring site to ca. 25 other sites in NW Texas, 2 near Ft. Stockton, and 4 between Presidio and Candelaria, TX. Beetles from Uzbekistan have been released near Seymour, TX and are established at Lake Meredith, and Fukang, China beetles at Artesia, NM. Crete beetles (from a culture at Albany, CA) are established at Cache Creek, CA. Biological control seems well on the way to providing efficient, safe, permanent, inexpensive and environmentally friendly control of saltcedar in the United States. We do not anticipate damage to native Frankenia plants (also in the order Tamaricales) and only slight to moderate, and only transitory damage to beneficial, exotic athel (T. aphylla) trees, and only if located adjacent to defoliated saltcedars.