Hydrilla verticillata is an aquatic weed that has been in the United States since the 1950s. It is found throughout most of the Southeast and parts of the western United States. Recently, in some parts of Florida H. verticillata is showing resistance to fluridone, the one herbicide approved by the U.S. Environmental Protection Agency (EPA) for systemic control. Researchers with the USDA’s Agricultural Research Service believe the resistance is a result of a gene mutation, making it the first report of herbicide resistance in an asexually reproducing higher plant. Biocontrol options are under investigation.
For the full story: http://www.ars.usda.gov/is/AR/archive/nov05/hydrilla1105.htm