Control Studies


Preventing invasive aquatic plants from reaching Connecticut lakes and ponds is the preferred method of control. People can move plants from one body of water to another on boats and trailers. Recent legislation (Connecticut Public Act No. 03-136) imposes fines on individuals found transporting invasive non-native plants in this way. Posting signs at boat launch ramps detailing what the plants look like and the importance of checking and cleaning boats and trailers can be helpful. Plants liberated from aquariums or water gardens are another way non-native aquatic plants are introduced into freshwater ecosystems. Properly disposing of aquarium plants and isolating water gardens will help reduce these risks.  Public Act No. 04-203 restricts the sale of most invasive aquatic plants in Connecticut.

Unfortunately, the spread of invasive non-native aquatic plants in Connecticut is likely to continue because large numbers of lakes and ponds already contain the plants and natural movement by flowing water and aquatic wildlife is largely uncontrollable. Eradication of new infestations is more likely to be successful than elimination of large areas of established plants. Volunteer monitoring programs can be initiated to routinely check water bodies for new plants. The Connecticut Agricultural Experiment Station Invasive Aquatic Plant Program (CAES IAPP) can offer assistance to volunteers on how to survey and identify aquatic vegetation.

Many techniques are available for controlling unwanted aquatic vegetation. Regardless of the method, knowing the potential harmful effects on non-target organisms is important. Mechanical control includes hand-pulling, machine harvesting, hydroraking, benthic barriers and dredging. Typically, these methods are used in localized areas. Dredging requires permits from local, state and federal agencies. Water drawdown, particularly during the winter, when freezing temperatures can damage plants, is a low-cost weed-control option. The Connecticut Department of Energy and Environmental Protection (DEEP) must be notified before any drawdown. Chemical aquatic weed control involves applying a herbicide to decrease the population of a plant. Invasive plants are rarely eliminated, but the recreational value of a lake or pond can be improved, and the spread of the invasive plant can be slowed. Selecting the proper herbicide and the time of application requires accurate information on the life cycle of the invasive plant. A permit from the state DEEP is required before an aquatic herbicide can be used. Experts at CAES IAPP and the DEEP can answer questions on the use of aquatic herbicides. Biological control agents, including beneficial insects and microbes, may someday be viable aquatic weed control alternatives. To date, the only biological control used successfully in Connecticut is a plant-eating fish, the grass carp (Ctenopharyngodon idella). This fish is not native and must be certified as sterile (triploid) to assure it will not reproduce in the environment. The DEEP monitors the release of this fish, and a permit is required before they can be purchased. Typically, grass carp are used in small ponds. Containment of grass carp to the body of water where they are introduced is required, and special screens are needed at inflows and outflows.  CAES IAPP started a project in 2006 to assess the distribution and abundance of biological control agents for Myriophyllum spicatum.  (Follow this link for more information on the biological control study.)

Because plants need nutrients to proliferate, reducing the nutrients reaching the water body may inhibit the growth of invasive aquatic plants. Maintaining unfertilized shoreline buffer zones and minimizing the misapplication of fertilizer to paved areas can reduce the amount of fertilizer that reaches lakes and ponds. CAES offers soil tests that determine fertilizer amounts based on plant needs.



1.  Control of Potamogeton Crispus and Myriophyllum Spicatum in Crystal Lake, Middletown, CT, 2009 (2.8 MB, 26 pages, PDF format*)

2.  Control of Variable Watermilfoil in Bashan Lake, CT with 2,4-D: Monitoring of Lake and Well Water(10.6 MB, 8 pages, PDF format*)

3.  Control of Milfoil in Bashan Lake, 2003 (493 KB, 14 pages, PDF format*)

4.  Control of Milfoil in Bashan Lake, 2001 (775 KB, 23 pages, PDF format*)

5.  Control of Aquatic Weeds in Lake Quonnipaug, 2003 (6.6 MB, 73 pages, PDF format*)

6.  Control of Cabomba, Eurasian Milfoil and water Lily in Lake Quonnipaug with Herbicides and Hydroraking, 2002 (682 KB, 17 pages, PDF format*)

7.  Control of Cabomba and Eurasian Milfoil in Lake Quonnipaug with Fluridone and 2,4-D, 2001 (511KB, 14 pages, PDF format*)

8.  A Diagnostic Feasibility Study of Moodus Reservoir, East Haddam, CT: Water Chemistry, Aquatic Vegetation Survey and Management Options, 2002 (2MB, 24 pages, PDF format*)