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Recent temps make fate of Candlewood’s pesky milfoil uncertain

February 7, 2019

DANBURY — Candlewood Lake visitors right now are greeted with a bed of dead Eurasian watermilfoil lining the shore — a welcome site for lake users.

But scientists who study the aquatic invasive plant are unsure what the recent cold snap, followed by the few days when temperatures climbed into the 50s and 60s could mean for the plant’s return this summer and next year.

“It’s difficult to get a real deep freeze with those conditions,” said Greg Bugbee, an associate scientist with the Connecticut Agricultural Experiment Station.

Milfoil has plagued the lake for years. It presents a safety risk for swimmers and gets tangled in boat propellers, which spread the plant throughout the lake.

Lowering the lake in the winter to expose the plants to freezing temperatures is a popular way to keep it under control at Candlewood Lake. FirstLight Power Resources, which owns and operates the lake, lowers the water levels each year, alternating between several feet and 10 feet. Right now the lake is 10 feet lower as part of a deep drawdown.

Historically, the deeper the drawdown, the less milfoil the following summer because more plants are exposed and killed by the winter’s deep freeze. But a lot of factors come into play to determine how successful it is, including how dry the sediment is, if the plants are insulated by snow or ice before the freeze sets in and the amount of time the temperatures remain below freezing.

This year, the sudden temperature flux might have meant the temperatures weren’t ideal for a long enough period. It’s also unclear if the milfoil was exposed or under snow.

“There’s no way for us to accurately predict what it will look like in the spring,” said Neil Stalter, Candlewood Lake Authority’s director of ecology and environmental education. “There’s so many variables.”

He said the authority is optimistic the few days of cold weather helped kill at least some of the milfoil.

Bugbee said the surface milfoil will die, but the root system will most likely survive and regrow if not this summer then next summer after a shallow drawdown.

“In most cases, you can assume regrowth,” he said, adding that drawdowns aren’t a long-term solution.

Larry Marsicano, a consultant for the lake authority now, said he worked with Western Connecticut State University when he was the authority’s executive director to determine the ideal climate conditions to kill the milfoil.

In those tests, the plant died when temperatures were at -5 degrees Celsius, or about 23 degrees Fahrenheit for 24 to 48 straight hours. He said that happened in ideal conditions in a lab and generally takes longer in the real world.

Marsicano said the study showed that a gradual thaw damaged the roots more than a quick thaw did. Though the study’s gradual thaw happened at 39 degrees Fahrenheit and the quick thaw happened at 77 degrees, he thinks the same principle applied to this season’s conditions.

The key for a successful freeze is the sediment temperature, which generally is warmer than the air and can be influenced by a warm stream coming in or ice or snow insulating it at freezing despite what the air temperatures get to.

“You’re hoping for a dry and cold soil layer to freeze out those root systems,” Stalter said.

He added the recent warm weather might have helped if it melted the snow and ice covering the roots, allowing for another chance for a deep freeze to set in.

“If we can get a cold snap and some cold nights without snow cover, that would be really helpful,” he said.

Bugbee said the greater mitigation might come from the sterile grass carp that were added to eat the milfoil. The fish are now 24 inches or so with quite an appetite and Bugbee said he wonders if the thousands of larger fish will eat the regrowth.

kkoerting@newstimes.com; 203-731-3345

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