Description:
Hydrilla verticillata is a member of the Hydrocharitaceae family. It closely resembles other members of this family such as Elodea canadensis (native to Washington) and Egeria densa (native to South America, though established in several Washington lakes). Several members of this family are popular with the aquarium and nursery industry because they are hardy, tolerant plants. Consequently, some have become severe pest problems where introduced to waters outside their native range.

• Mechanical: Because this plant spreads readily through fragmentation, mechanical controls such as cutting and harvesting should be used only when the extent of the infestation is such that all available niches have been filled. Using mechanical controls while the plant is still invading, will tend to enhance its rate of spread.
• Biological: Worldwide surveys for natural hydrilla enemies were begun in 1981 in a cooperative study between the University of Florida, the United States Department of Agriculture, and the United States Army Corps of Engineers. A number of insects were identified, quarantined and tested, and eventually released in Florida and other states. Results from these insect releases are still being evaluated. However, most of these insects were collected in tropical areas of the world and it is doubtful that populations could establish in Washington.
• Herbicide: There are three EPA-registered herbicides effective against hydrilla growth that are permitted for use in Washington. These are fluridone (Sonar®), endothall (Aquathal®), and copper compounds. Fluridone is a systemic herbicide that has proven effective against hydrilla in Florida and other states. The drawbacks to using fluridone include its high cost, slow-action, and non-selectivity toward other macrophyte species. However, it is the herbicide of choice. Endothall, a fast-acting contact herbicide, is used when immediate control of vegetation is needed. Copper compounds are often used in conjunction with endothall applications, although copper by itself exhibits herbicidal action against hydrilla. Copper is also used for its algicidal properties when heavy periphytic growth on the hydrilla may interfere with herbicide uptake. These herbicides do not affect hydrilla seeds, tubers, and turions and repeated applications are needed to control hydrilla regrowth. Refer to the State Noxious Weed Control Board site

For More Information:
Detailed information about Hydrilla is available at the Washington State Noxious Weed Control Board Web Site.