Curly leaf pondweed is native to Asia and escaped into American waterways in the late 19th century. A century later, it has invaded bodies of water all across the continental United States, with the exception of Maine. Although it is difficult to eradicate, there are several effective methods available to bring it under control and minimise its spread. These include aquatic herbicides, physical cutting of the weeds and modification of their growing environment. A combination of these techniques can minimise the weed's impact.
Prevent the spread of pondweed, by demonstrating high standards of boat hygiene. Be sure your boat and trailer are free of any traces of vegetation before placing them in a given body of water. This will help curtail the spread of the weed.
Treat affected areas in early spring, when pondweed has emerged but indigenous species have not. Use a formulation of diquat or endothal, two herbicides with demonstrated effectiveness against curly pondweed. Fluridone is also effective but works more slowly.
Cut or pull up the weeds manually early in the season, before their reproductive cycle is in full swing. Take at least the top 5 feet of each plant for best effect.
Rake the plants at the lake's bottom to uproot and kill them. Some companies manufacture machines to do this automatically through the summer. Their primary purpose is to keep swimming areas clean, but they work just as well for pondweed control.
Reduce the pond's water level in fall to expose the pondweeds and their rooting buds, or turions. The combination of drying out and freezing kills them effectively.
Dredge the bottom to deepen it past the 15-foot limit of the pondweed's habitat. This is a drastic step that also prevents the growth of local species.
Consult with your county extension agent before applying any herbicide or taking any action to dredge a pond or lower its water level. Any or all of these actions may require special permits, and the application of herbicides may require specialised advice from the extension agent or other local authorities.