Treatments

Treatment of Variable Milfoil

Management methods currently include mechanical removal, drawdowns, and herbicides. No known biological controls exist.

Harvesting

Although harvesting can greatly reduce the Variable Milfoil biomass in a water body, harvesting also causes fragmentation, and fragments are capable of producing new plants. Some fragments may drift down stream or attach to boats and wildlife and create new infestations elsewhere.

BLIMP hires certified divers to pull milfoil in Maine, where chemical treatment is not allowed. Divers also pull in isolated areas of New Hampshire.

Herbicide Treatments

Most recently on Balch, (June 13, 2007) we have chemically treated infested areas in NH. including the river and all the way into Woodman Lake. Read the News section for details.

Benthic Barriers

This will be new for Balch in 2007 or 2008. Benthic ("bottom") barriers involve covering selected milfoil-infested areas with impermeable sheets that, when left in place for 60 days, kill the plants, roots & all.

There are different types of barriers now in use.

For areas that are heavily infested, he has been using 10 ft x 10 ft pieces of geotextile material (used in construction under rip rap, etc) weighted with 6 pieces of 10 ft rebar. The material is rolled up, placed on a boat, and unrolled in place by a diver. After 60 days they are removed & can be placed in a new location - so 2 locations/ mat can take place for each barrier in one summer. In Lily Brook, 80 mats were placed & killed all the milfoil in a 8000 sq ft area. They have been so successful that they have mats available for rent for other lakes that want to test the method. In 2007, a new system will be tried for large infestations, that involved using 10 ft x 40 ft of 6 mil plastic sheeting & rebar. This may be faster & more efficient than the smaller barriers.
For individual, isolated milfoil plants, a 5 ft x 5 ft "clamshell" barrier tcan be put in place by a single person from a boat - left in place for 60 days & removed, resulting in one dead plant. The advantages over pulling that plant are - only one person is needed, and no fragments are produced.

Jim Chandler, who has performed control projects on Bryant Pond, Shagg Pond & Lily Brook, recommends that no more than 10% of a lake be covered with barriers at one time - this won't be a problem for Balch. Monitoring has shown that 1-2 years after using barriers, native plant species return fully within 1-2 years with no return of the milfoil.

If we sound enthusiastic about this method, well - we are. We think that we should rent a few barriers & try them out this summer - if successful we could build our own - the current estimated cost from Jim is $0.10/sq ft or $40/ large mat.

Drawdown