Integrated management of aquatic invasive plants to improve flows and water quality in the Rio Grande, Texas

E. Chilton¹ and T.L. Arsuffi².¹Texas Parks and Wildlife Department, 4200 Smith School Road, Austin, TX 87844, ²Field Station, Texas Tech University, Junction, TX 76849

The Rio Grande provides water for agriculture and municipalities along the South Texas border with Mexico. In 1997–1998 water hyacinth and hydrilla infestations below McAllen, Texas began to interfere with water transport downstream. The Rio Grande Water Master reported the need to release up to 30% more water than demand called to push water through weed beds. At times the Mexican city of Matamoras was unable to get adequate drinking water, and by 2001 the mouth of the river closed. Bi–national jurisdiction made use of herbicides difficult and mechanical techniques were initially the primary form of vegetation management. Use of triploid grass carp and herbicides in 2003, and increased rainfall drastically reduced exotic plant infestations in the lower 175 miles of the river. However, hydrilla has now become a problem in the Rio Grande from McAllen upstream to International Falcon Reservoir–2005 surveys/estimates showed 100 river miles with 50–100% hydrilla coverage. Hydrilla flies have been stocked, and use of triploid grass carp is again planned. Cooperation and planning among federal, state, local, and Mexican officials has been vital to management efforts, and will be necessary to deal with growing aquatic and riparian vegetation problems of the Rio Grande.