Public Meeting - Milfoil Control with Herbicide

posted Apr 12, 2017, 5:44 PM by Lake Iroquois Association   [ updated Apr 12, 2017, 5:53 PM ]

Vermont Agency of Natural Resources

Aquatic Nuisance Control Public Informational Meeting Notice

The towns of Hinesburg and Williston have requested the Department of Environmental Conservation hold a public information meeting on the draft decision for Aquatic Nuisance Control draft permit 2240-ANC, which pertains to the proposed use of an aquatic herbicide, Sonar AS, in Lake Iroquois.

The public information meeting will be held at the Hinesburg Town Hall:

10632 VT-116, Hinesburg, VT 05461

Thursday May 4, 2017

6 PM – 8 PM

Written comments may be submitted to Comments received by the Department of Environmental Conservation during the public notice period, which expires on 4/21, or at the public information meeting shall be taken into consideration in the decision, which will be formalized in a Response Summary that shall be issued with the decision.


The mission of the Lake Iroquois Association (LIA) is to maintain and enhance water quality and a healthy ecosystem in Lake Iroquois. LIA has been working for many years to control and prevent the spread of Aquatic Invasive Species (AIS) into the lake. However, even with all of these efforts, which are ongoing, the infestation of Eurasian Water Milfoil (EWM) has spread to the point that it has severely impacted the use of the lake, squeezed out many native species, and has in some areas become so dense and matted that it has caused algae blooms on the lake surface. With no natural limitations, this serious infestation could continue to spread and destroy large portions of the lake ecosystem. After discussions with many lake associations around the state, state Department of Environmental Conservation officials, and other experts, the LIA decided to pursue a lake-wide use of herbicides. The LIA in partnership with the Town of Williston applied for a state permit to use Sonar A.S.  (active ingredient fluridone). Eurasian Water Milfoil is a broadleaf plant and is sensitive at very low concentrations of 5-8 Parts Per Billion, well below the drinking water levels set by the US EPA (150 PPB) and the State of New York (50 PPB). Sonar has been widely used in Vermont and around the country and it has been tested and studied for many years. 

For more information please visit:  

What is Eurasian Water Milfoil(EWM) and why is it a problem now?

      EWM is an invasive aquatic plant. It is spread by fragmentation. EWM forms thick mats that prevent swimming, paddling, sailing, fishing and motor boating.

      If uncontrolled the problem could worsen and existing infested areas could increase in density.

      Milfoil has become the dominant aquatic plant in the lake, creating a monoculture of EWM in some areas, causing the native aquatic plant species to disappear (1984 45 species, 2012 35 species, 2014 33 species)

Why use an herbicide and is it safe?

      Using the herbicide Sonar is the most cost effective technique that will least disrupt the lake ecosystem, allowing for control of this lake-wide infestation.

      Diver Assisted Suction Harvesting is very expensive, removes native plants and disrupts the lake bottom.

      Benthic barriers are very expensive, block all plants from growing and need to be removed annually.

      Weevils were tried but couldn’t be procured in sufficient numbers to be effective.

      Sonar is safe, it will be used in concentrations(5-8 Parts Per Billion) below the drinking water levels set by the US EPA(150 PPB) and State of New York(50 PPB).

      The application will be done by a professional application company and will be monitored independently.

      Sonar breaks down in the environment and doesn’t accumulate in plants or animals.

Will this one treatment remove all Eurasian Water Milfoil from the lake?

      Unfortunately, once EWM is in a water body, it is almost impossible to completely eradicate it. The goal of this program is to control EWM in the lake, so it isn’t a nuisance.

      In subsequent years, Benthic Barriers will be installed at the fishing access to maintain a clear channel and prevent fragmentation and spread by boats entering and leaving the lake.

      Regular surveys of the lake will be done to monitor the situation and track any recurrences.

      Another herbicide treatment may be needed in 4-5 years but will depend on recurrence and effectiveness of lake monitoring and mechanical removal before it spreads.

Pat Suozzi                                Jamie Carroll                                                     Chris Conant

LIA President                           LIA Director & Milfoil Chair                 LIA Secretary and Fundraising Chair


Lake Iroquois Association

PO Box 569 Hinesburg, VT 05461