First phase of 2024 hydrilla treatment underway at East Twin

SALISBURY — Targeted hotspots of the invasive aquatic plant hydrilla around the marina and in the northeast cove of East Twin Lake were treated on Monday with a controlled release herbicide known as Sonar One.

Subsequent dosing with the herbicide, used for the first time at Twin Lakes, will be repeated at intervals of about three weeks for the remainder of the summer and into the fall, according to Twin Lakes Association (TLA) officials.

“Sonar is the preferred herbicide for hydrilla,” Russ Conklin, Vice President of Lake Management for the TLA, had reported during the lake association’s recent membership meeting in June.

The TLA worked with scientific advisors from the U.S. Army Corps of Engineers (USACE) and the Connecticut Agricultural Experiment Station (CAES), as well as the TLA’s limnologist, George Knoecklein, founder and principal of Northeast Aquatic Research (NEAR), regarding which herbicides have proven most effective in the management of hydrilla.

The group recommended Sonar One, a slow-release version of Sonar, which contains fluoridone as its active ingredient. Fluoridone is absorbed by hydrilla’s roots and shoots and is then transported throughout the plant, disrupting photosynthesis and preventing the plant from producing pigments that protect it from sunlight, causing the plant to bleach and die over time.

The TLA, through its contracted herbicide applicator, The Pond and Lake Connection, has received a permit for treatment specifically with Sonar from the state Department of Energy and Environmental Protection (DEEP).

The first dosing of slow-release Sonar by The Pond and Lakes Connection took place Monday. Signs of plant damage may appear within seven to 10 days of application, but it may take 30 to 90 days of continuous application to kill hydrilla.

Sonar has no labeled restrictions on swimming, watering or fishing when used as directed, according to TLA officials. The herbicide was approved for use by the U.S. Environmental Protection Agency in 1986 and has been widely used since then.

“From the literature we have reviewed including product label, and based upon the recommendation by our scientific experts, and given the decades of wide use in the United States including on lakes that are battling hydrilla, we believe this is the appropriate choice for our lakes at this time,” said TLA president Grant Bogle.

NEAR, the firm hired by the TLA to conduct water quality testing and aquatic plant surveys, recently conducted an aquatic plant survey of the entire Twin Lakes system and, as expected, found numerous beds of hydrilla around O’Hara’s Landing Marina.

Last fall a four-acre area was spot-treated with a different herbicide, ProcellaCOR, just before the hydrilla started to naturally die back and overwinter, but the noxious weed resprouted this summer.

“Last fall’s treatment did not occur until mid-September and, as such, was late,” Bogle explained. “You want to catch hydrilla as it is emerging and in the growth phase. That said, ProcellaCOR did have an impact on the standing crop but did not appear to kill the plant to the roots. We fully expected it to come up again this spring.”

One stray patch of hydrilla, identified north of the marina, was not targeted for treatment last year, or this year, because a state-listed protected native species, water marigold, grows in the area. The patch is currently blocked off with barriers to keep unsuspecting boaters from chopping off hydrilla fragments, which can then contaminate other areas of the lake.

East Twin was identified late last June as the first lake in Connecticut infected with the non-native plant, even though TLA’s Conkln said he believes it may have gone unnoticed in East Twin for several years. Since then, the strain has also been discovered in six additional lakes in the state.

“We know it’s on the move, so it’s very concerning,” said Gregory Bugbee, associate scientist with CAES and scientific advisor to the TLA in its battle against hydrilla. Bugbee and other environmentalists said there are still a lot of “unknowns” surrounding the non-native weed and the effectiveness of treatment efforts to date.