PARENT SESSION
Poster Session: Invasive Plant Management in Different Habitat-Case Studies and Models of Success
Wednesday, November 5, 2003, 5:00 PM to 7:00 PM
Global Ballroom

Case study: Survey and eradication of Hydrilla verticillata in Clear Lake, California.

Dechoretz, Nathan ^*,1, Leavitt, Robert¹, ¹ California Department of Food and Agriculture, Sacramento, CA, USA

ABSTRACT- Biologists from the California Department of Food and Agriculture (CDFA) and the Lake County Department of Agriculture discovered hydrilla [Hydrilla verticillata (L.f.) Royle] in Clear Lake during a routine survey in August 1994. (Clear Lake is the largest freshwater, natural lake completely within California. It has approximately 43,000 surface acres and an average depth of approximately 26 feet.) Plant specimens were identified as hydrilla by the CDFA Plant Pest Diagnostic Center, Botany Laboratory, and confirmed to be the monoecious form by the United States Department of Agriculture, Agricultural Research Service, Exotic and Invasive Weed Unit. The CDFA and the Lake County Agricultural Commissioner put Lake County under quarantine because of the high risk that plant fragments, tubers, or turions could be spread by human activities associated with the lake. The CDFA began a hydrilla survey of the entire lake, and started eradication treatments with copper-based aquatic herbicides within two weeks of the first detection. The CDFA convened a Scientific Advisory Panel (SAP) in late 1994. The SAP recommended that hydrilla be eradicated from Clear Lake, found eradication to be feasible, and outlined an eradication program. The CDFA began to use fluridone in 1996 after it was registered by the California Department of Pesticide Regulation. The CDFA divided the lake into 82 management units. The number of infested management units peaked at 54 in 1998 and has decreased to six in 2002. Starting in 1997, it became feasible to count individual hydrilla plants and plant mats (finds). In 1997 there were 208 finds in the lake; this has decreased to 12 in 2002. Starting in 2000, some management units have been hydrilla-free for over three years.

Key words: california, hydrilla, fluridone