King County's hydrilla eradication project seeing good results, but still ongoing

King County’s Pipe and Lucerne lakes are the only waterbodies in the Pacific Northwest where the tenacious aquatic weed hydrilla has been found, and the King County Lake Stewardship Program hopes to wipe out the fast-growing plant before it can spread elsewhere.

King County has scheduled a public meeting for Nov. 6 to talk with the community about the hydrilla infestation, past efforts to eradicate the weed, plus future management options, at a Nov. 6 meeting in Maple Valley. The meeting is set for 7 p.m. at the Lake Wilderness Lodge, 22500 SE 248th St.

“We want to eradicate this hydrilla infestation before it gets a chance to get into other water bodies,” said Beth Cullen, a water quality planner in King County’s Lake Stewardship Program. “Once this plant gets established, it can be very difficult – and very expensive – to deal with. For instance, the State of Florida spends more than $11 million a year on hydrilla eradication – just to keep waterways open and navigable.”

Hydrilla has several ways of reproducing, including fragmentation, in-ground tubers and above-ground trailing shoots. Tubers can lie dormant and unaffected by herbicides in the sediment for up to four years before sprouting.

King County has been treating the hydrilla infestations in Pipe and Lucerne lakes since 1994. A new treatment approach was taken in 2003, when a slow-release herbicide, Sonar PR, was applied to the infested areas. Low levels of the herbicide were continually applied during the hydrilla growing season to kill the plants as they sprouted.

The new approach worked: In 2003, King County crews counted 240 hydrilla plants in the two lakes; This year, just two plants were found in Pipe Lake, while no hydrilla plants have been found in Lucerne Lake since 2004.

“We’re working hard to get hydrilla out of Washington,” Cullen said. “We don’t want to deal with the large-scale ramifications if this weed were to colonize in other lake systems.”

More information about King County’s hydrilla eradication project is available at http://dnr.metrokc.gov/wlr/waterres/smlakes/stophydrilla.htm on the Internet.