Hydnlla Management in Lake Conroe, Texas: A Case History

摘要

Lake Conroe has long been synonymous with the controversy surrounding control of the exotic plant hydrilla Hydrilla verticillata. By the time hy-drilla was first identified in Lake Conroe in 1975 (2 years after impoundment), the plant covered 470 acres. By 1979, hydrilla increased to 4,500 acres and was causing problems for boaters, skiers, and swimmers. As a result of efforts by the Lake Conroe Association and its supporters and despite objections by Texas Parks and Wildlife Department (TPWD) staff,the Texas Legislature directed the Texas Agricultural Experiment Station and TPWD to conduct a study to determine the ability of grass carp Ctenopharyngodon idella to control hydrilla and the effects of hydrilla removal on fish populations, the fishery,and the limnology of the reservoir. Between September 1981 and September 1982, 270,000 diploid grass carp were released into Lake Conroe. By October 1983 hydrilla and all other aquatic vegetation had disappeared from the reservoir. Hydrilla growth was suppressed in Lake Conroe for the next 13 years; however, in 1996, approximately 3 acres of hydrilla were discovered. For the next 8 years (1997—2004), herbicide treatments funded primarily by the San Jacinto River Authority (SJRA) and conducted by SJRAand TPWD successfully limited hydrilla expansion. At the same time, native vegetation establishment by TPWD, U.S. Army Engineer Environmental Research and Development Center's Lewisville Aquatic Ecosystem Research Facility, and several angling groups ledto diversification and expansion of the native aquatic plant community in Lake Conroe and provided an alternative to a monoculture of hydrilla for fish habitat. However, by 2005, herbicide treatments alone were unable to control hydrilla expansion. As aresult, TPWD and SJRA determined the need to develop a comprehensive hydrilla management plan for Lake Conroe. Therefore, a plan based on the principles of Integrated Pest Management was developed with the cooperation of angler organizations, property owner associations, local businesses, and other user groups. The plan integrated use of ecological, biological, chemical, and mechanical strategies for control of hydrilla while promoting diversity of the aquatic plant community. The stated time line of the plan was to reduce the surface coverage of hydrilla at Lake Con-roe to less than 40 acres by spring of 2008, while preserving a diverse aquatic plant community.