Management methods currently include mechanical removal, drawdowns, and herbicides. No known biological controls exist.
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.
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.
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.
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.
Drawdowns can be an effective mode of Variable Milfoil control if the drawdown is extensive enough to prevent re-growth from seeds. Drawdowns may impact fish, aquatic organisms, reptiles, amphibians and downstream conditions. This type of drawdown would be more extensive than the typical drawdown we do on Balch each year. It is not a method we use to control milfoil.