Weevils get to work in Capitol lake

OLYMPIA - A three-year pilot project using an aquatic beetle to tackle a milfoil infestation in Capitol Lake is off to a good start.

On Wednesday, a team of scientists from Ohio-based EnviroScience surveyed a 3-acre lake lagoon where, in mid-August, they released about 12,000 weevil eggs and larvae in hopes they would bore into the stems of the milfoil plants and mature into weed-munching adults.

The pond next to the Capitol Lake Interpretive Center has the densest pockets of milfoil left in the 250-acre lake since it first was infested in 2001.

“I’m happy to see there is damage on the plants,” said Nancy Cushing, an EnviroSciences aquatic biologist.

EnviroSciences specializes in biological control of milfoil invasions in lakes by capturing and rearing native aquatic weevils that feed on milfoil, then releasing them by the thousands where milfoil invasions occur.

The $75,000 Capitol Lake project financed primarily by the state Department of Ecology is the first large-scale use of milfoil weevils in Washington, company President Martin Hilovsky said.

One of the first things the scientists discovered is that the milfoil in Capitol Lake is a hybrid variety of Eurasian water milfoil and native North American water milfoil. It originally was thought to be all Eurasian water milfoil, an aggressive, invasive weed.

Either way, the milfoil in the lake, left unchecked, can choke out other native aquatic plants, hinder recreational use of the lake and serve as a platform for floating mats of algae.

The weevils spend most of their life span, which is roughly 30 days to 90 days, submerged in the water, Hilovsky said.

The weevil larvae bore into the stem of the plant, causing the plants to collapse and sink to the lake bottom. As adults, the weevils eat milfoil leaves and stems.

“It’s an environmentally friendly, self-sustaining form of biological control,” Hilovsky said. “The downside is that it is not a quick fix.”

After milfoil was detected in the lake eight years ago, it quickly spread to cover large sections of the lake.

In July 2004, the state Department of General Administration hired a contractor to spray the herbicide triclopyr in the middle and south basins of the lake to kill the pesky aquatic weed.

But as expected, the chemical treatment did not completely rid the lake of milfoil. In subsequent years, crews have been hired to hand-pull spot infestations of the weed.

The most persistent infestation has been in the pond next to the interpretive center.

In 2007, the pond was drained and the weeds were pulled, but they completely rebounded within one month, General Administration senior planner Nathaniel Jones recalled.

The state agency decided to try biological control in lieu of more hand-pulling, Jones said.

“We’re trying to avoid reinfestation of the lake,” Jones said. “We’re also really trying to further the science of milfoil control.”

John Dodge: 360-754-5444

jdodge@theolympian.com