AUGUSTA, Maine - A herbicide treatment to help eradicate an invasive weed from Milton Three Ponds appears to have been successful after much of the weed was found turned brown and had sunk to the bottom just days after its application to 41 acres in Northeast Pond.
The chemical application of diquat was performed by SOLitude Lake Management on July 26. Maine DEP collected water samples for diquat concentration analysis on July 26, 27, 28 and 31, showing the herbicide concentrations had diminished rapidly since the treatment. The latest diquat concentrations are still above the reporting limit, meaning there will be at least one additional sampling round, a press release announced on Friday.
The effect of the herbicide was evident on July 28 as most of the floating-leaved vegetation (much of it is little floating heart) within the treatment area had turned brown. By July 31, some of the beds of little floating heart had sunk to the bottom. John McPhedran of Maine DES said he expected this to happen with other beds as well.
This result was expected since diquat is not selective and kills both submerged and emergent plants, McPhedran said, adding it causes rapid die-off of the shoot portion of the plant it contacts but is not effective on roots, rhizomes or tubers.
The objective of the treatment was to kill European naiad before it sets seed. Officials are not concerned about the roots because the entire plant dies back each winter.
New England Milfoil began removal on July 31 of smaller patches of European naiad in other areas of Northeast Pond, the press release noted.
Many of the European naiad plants NEM is finding are still relatively small and are mixed with natives, making for challenging removal.
Lake surveyor Dennis Roberge of Shapleigh continues to assist by surveying and marking patches for removal.