A July 5 letter to the editor questioned spending $565,000 to relocate a public boat ramp on Messalonskee Lake instead of eliminating its invasive Variable milfoil infestation directly with herbicides as other states do. Here's the answer.

Herbicides can be effective in controlling as well as reducing plant infestations. They allow recreation and other lake uses without the nuisances caused by invasive plants.

But such relief is only temporary.

Herbicides are one option the Maine Department of Environmental Protection (DEP) evaluates when addressing any of Maine's infested lakes, but they're not for Messalonskee. There is no practical evidence that shows this choice is feasible for large water bodies like this lake.

Indeed, states with aggressive herbicide programs for plant control commit significant resources that include the regular re-treatment of lakes, a regimen DEP is not prepared to undertake on Messalonskee.

Herbicides can address a target spectrum of plants, but they aren't plant-specific, which means many "good" native plants in a given ecosystem will be hurt along with the "bad" invasives when they're used. We need to protect native plants that provide a lake with defenses necessary to compete for habitat against an intruding invasive plant species. If native plants are removed, more aggressive invasive plant species will have the competitive advantage when they return ... and they will return. In time, a bad problem becomes worse.

While $565,000 seems like plenty for herbicides, the math shows spot treatments would be required along Messalonskee Lake's perimeter, and a substantial portion of the south end as well as Belgrade Stream would have to be treated -- repeatedly. Messalonskee alone is 3,691 acres, and herbicide costs range between $200 and $600 per acre. Even repeated herbicide treatments would not eliminate the source of plant fragments that infiltrate the now-closed Route 27 ramp.

The one-time cost for the new boat ramp and closure of the old, heavily infested one is a bargain.

Of course, prevention is the most cost-worthy option. Significant volunteer efforts reported in these pages include rampside boat inspections, surveying of lake shores, and rapid removal of newly found plants. These efforts are proving effective in preventing infestations.

Also effective is limiting the opportunity for contact between people and offending plants. That's just what will be accomplished by the Maine Department of Conservation in its decision to close the Route 27 ramp.

Recent years showed that 49% of boats leaving this ramp have had plants hitchhiking on boat props, boat trailers and other gear. Boat traffic directed away from a site as risky as the Route 27 boat ramp will prevent spreading Variable milfoil throughout Messalonskee and into neighboring lakes.

Paul Gregory, is an environmental specialist with Maine Department of Environmental Protection Invasive Species Program.