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Herbicide to Kill Milfoil Shows Progress in Salmon Lake in Belgrade

October 13, 2009 - BELGRADE -- Early signs are encouraging that a herbicide used last month to kill an invasive milfoil in Salmon Lake is beginning to work.

The chemical, applied in September to kill the highly aggressive Eurasian milfoil, has started to kill the plants, said John McPhedran, invasive aquatic plant specialist for the Maine Department of Environmental Protection.

"When we've gone to those places we've marked with the buoys, we have not seen the milfoil," McPhedran said. "That's been good to see. It's what we expected."

The milfoil, which can form dense mats and congest waterways, was first discovered in Salmon Lake's Kozy Cove in August 2008.

Divers began removing the plant from the 6-acre cove within a week of the discovery, but it continued to swell.

Divers removed 325 plants this summer, more than twice the number removed last year.

The department announced in July it was seeking a permit to spread the chemical 2,4-Dichlorophenoxyacetic acid – better known as 2,4-D and by its trade name Navigate – to control the milfoil in the cove near the Salmon Lake outlet stream.

The department, after two public hearings, applied the chemical Sept. 10.

State officials hope the herbicide will push the milfoil back to a level where it can be controlled through dives or other harvesting methods.

"That's still our hope, but it's still a long-term effort to get this plant under control," McPhedran said. "It's not a one-and-done project."

Exactly how well the herbicide treatment is working remains a mystery because of the yearly algae bloom.

"The water is cloudy and green," McPhedran said. "It makes it difficult to see well. We haven't been able to conduct a thorough survey yet."

The algae is starting to clear with the arrival of cooler temperatures, but time is needed to know how the herbicide worked.

"We won't know the ultimate effectiveness until next year when the aquatic plant begins to grow again," McPhedran said.

The department continues to regularly test water samples from the cove and surrounding area for the presence of 2,4-D. The swimming restriction was lifted three days after the application, but an advisory against drinking and irrigating with lake water remains in place.

Results of testing on Sept. 25, the most recent available, showed 470 to 630 parts per billion of 2,4-D in Kozy Cove, just below the Salmon Lake dam; and in Hatchery Brook, the outlet stream from Salmon Lake into Great Pond.

The sampling showed just 5.7 parts per billion in Salmon Lake and no 2,4-D was detected in Great Pond.

Another sample was taken on Thursday. The monitoring will continue until there is no traceable level of herbicide at any of the locations, McPhedran said.

The herbicide's impact on other nontargeted plants will not be known until next year, McPhedran said. The department expects some damage.

There is no indication the herbicide has harmed wildlife. Fish and other wildlife were visible and healthy during a recent visit to the area, McPhedran said.

"In terms of effects on other organisms, we have not observed any direct negative effects on fish, turtles, and we haven't heard any reports from residents in the area," McPhedran said.

By CRAIG CROSBY, Kennebec Journal October 12, 2009


Lakes: Salmon (Ellis) Pond
Regions: Belgrade


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