Milfoil in Ossipee Lake
State limnologist recommends 2,4-D treatments
November 19, 2009
OSSIPEE — A state expert on milfoil control this week fielded questions about the safety and effectiveness of a widely used herbicide that targets this aggressive weed.
Amy Smagula, the state's exotic species program coordinator with the NH Department of Environmental Services, spoke at Monday's select board meeting at the invitation of the Ossipee Conservation Commission. Members of neighboring lake associations from Freedom and Effingham also attended the session. While state funding for invasive species control has dried up this year, the town could choose to replenish its milfoil control fund via a warrant article. But the board did not take action at the Monday meeting. Groups such as the Ossipee Lake Alliance has used non-chemical methods to remove milfoil from the late, but state officials believe the extent of the new and rapid spread of weeds requires more aggressive action.
Infested areas of the Ossipee Lake system include 8.7 acres of Pickerel Cove, 4.1 acres of Phillips Brook, a tributary in Leavitt Bay, and an inlet in Broad Bay. New milfoil infestation has been detected in Pickerel Cover and the weed has been spreading from Phillips Brook into Leavitt Bay.
Smagula discussed chemical and nonchemical treatments, and spent much of the time fielding board members' and residents' questions about the safety and effectiveness of the herbicide, 2,4-D.
Select board chair Kathleen Maloney inquired about the safety of this herbicide. "When all the plants are dying what's going got happen with the fish? How far is the herbicide going to spread? How will it affect water quality?" she asked.
Smagula replied that 2,4-D has been used since the 1920s in agricultural settings and on crops around the world; it has been used in aquatic systems since the 1940s, and in New Hampshire since the 1060s. She said the herbicide has been extensively studied.
"Two-four-D and 10 other (herbicides) were reviewed by the U.S. Army Corps of Engineers Environmental Research Center and of those, 11 total, 2,4-D was proven to be the most effective on milfoil, the most selective to milfoil, with no impact to non-target species. 2,4-D doesn't migrate to groundwater. It binds quickly to sediment and doesn't really move through the soil to the wells," said Smagula.
She said the state conducted a study on lower Sunset Lake in Barnstead, which has very sandy subsoil. The state tested a well very close – about 10 feet – to the herbicide application area. "We pumped that well routinely and that well did not draw the herbicide in even though the herbicide was applied adjacent to where the well was. So we no longer have that concern," said Smagula.
She added that other New England states have conducted studies with satisfactory results. Another problem with milfoil is that fragments can float or be blown from one part of a lake to another, or can spread when weeds hitch a ride on the bottom of uninspected boats.
Select board member Harry Merrow questioned nonchemical treatments, such as hand pulling and barriers that seemed to have worked well in other areas.
Smagula said barriers work well in small areas with limited water flows; but in sections of the lake where there is significant flow and shifts in water levels, barriers can be pulled out. She said barriers are most effective in areas no larger than 10 by 20 feet. Another problem is that even though the barriers are netted and weighted down to just above the bottom of the lake, gases released by the vegetation come up and cause the barriers to billow. This billowing creates a navigational and swim hazard.
She noted as well that the state is working with towns and community groups such as the Ossipee Lake Alliance on ways to control the spread of milfoil. Some control work is planned for Danforth Bay in 2010. She said the state might take further action to restrict movement of the weed, such as apply netting to contain fragments. One other issue for Ossipee Lake is that it is a very large, interconnected lake system. "The potential for milfoil spread is still there, and so action is definitely recommended in terms of containment and control," she added.