From a distance, purple loosestrife brightens up aquatic landscapes with its vibrant purple flowers. With a height of 10 feet tall and spanning five feet wide, this plant can form a dense carpet through which mazes can be formed.
And producing over 2.5 million seeds once mature allows purple loosestrife to outcompete native vegetation and take over a site once it becomes established. The loss of native vegetation negatively impacts nesting habitat for birds, and purple loosestrife doesn’t provide as good of erosion control as native vegetation.
Grays Harbor County is one of three counties with more than 1,000 acres of this Class B noxious weed; the Washington State Noxious Weed Control Board defines Class B noxious weeds as “nonnative species whose distribution is limited to portions of Washington state, but may be widespread in other parts.” A native of Northern Africa, Australia, Europe and Asia, purple loosestrife was listed in 1988 and is on the state’s quarantine list.
Earlier in July, the Grays Harbor Noxious Weed Control Board and partners led a concerted effort to begin reducing the acreage of purple loosestrife. Over four days, the team treated 50 acres on a section of the Chehalis River between Montesano and Cosmopolis.
Of this accomplishment, “that’s pretty impressive,” said Danika Davis, the Grays Harbor County Noxious Weed Control Board coordinator, and one of the staff involved in the treatment.
That this accomplishment came together on a relatively quick turnaround also adds to its being impressive because there is a narrow window during the summer to treat purple loosestrife.
“[Purple loosestrife] has look-alike plants that are difficult to distinguish when in early stages of growth,” Ben Doan, a crew supervisor with the Washington state Department of Ecology shared via email. “Purple loosestrife also has higher chemical uptake while flowering. Due to all of these factors, the window for treating purple loosestrife is often quite small.”
The imputes of this project began in the summer of 2024. Lauren Kuehne, owner of Omfishient Consulting, was contracted to survey the main stem of the Chehalis River for purple loosestrife, Brazilian elodea, knotweed and parrotfeather, all aquatic noxious weeds.
“[Kuehne] identified this section on the main stem Chehalis, right around Montesano, as huge hotspot and that’s where the most amount of purple loosestrife was observed between, just up from Montesano down to upstream of Cosmopolis,” said Sofia Sherman, the Chehalis Basin noxious weeds coordinator and an employee of the Confederated Tribes of the Chehalis Reservation.
This hotspot had “been known about for a while, but it was brought to my attention last year,” Davis said, adding that as for when the purple loosestrife first arrived on that site, can’t be determined but “based on its size, it’s definitely been around for a while.”
Davis, along with an employee with Washington Department of Fish and Wildlife (WDFW) and Kuehne, visited the site and decided it was doable to treat it, but her staff of three and a rowboat couldn’t do it alone. When Sherman began her position in March 2025, she promptly began the discussions to pull the project together.
“She really put her heart and soul into it,” Davis said. “Most of the time when we’re doing projects like this, what takes the most time is getting a hold of landowners [because] we got to get written permissions from every single person.”
The project would involve private landowners, and local and state agencies, the latter which included WDFW, Washington state Department of Natural Resources, the city of Montesano, Grays Harbor County and the Port of Grays Harbor. Although not all the private landowners signed onto the project, most did, and those landowners who chose not to participate had their parcels skipped.
The team consisted of 13 people who worked for DNR, WDFW, and Grays Harbor Noxious Weed Control Board staff, and a Washington Conservation Corps (WCC) crew; Sherman secured a donation from the 10,000 Year Institute, a nonprofit based out of Forks, for their WCC crew. WCC is a program within the Department of Ecology with a mission “to conserve and enhance the natural resources of Washington while providing meaningful service opportunities to young adults and military veterans.”
“There’s no way we would have been able to get half done with what we got without [this crew],’ said Davis.
Treating the purple loosestrife took four days and required a combination of airboats, because sites further down the river could only be accessed by boat, and on foot. Once on the shoreline, the crew members would walk into the patches.
Given the maze-like conditions the team encountered, Davis said they had to have a lot of communication between crew members and they would orient themselves with a visual, such as a line of willow.
Sherman recalled being shocked by how much purple loosestrife there was.
“I saw Lauren’s survey points and was like, ‘Yeah, I thought I had an understanding of what we were getting into,’” Sherman said.
Being surrounded by the purple loosestrife felt “unreal,” Sherman said. “There were places where we had our backpacks on and there’s purple loosestrife in all directions surrounding us, above our heads.”
Of the methods to control purple loosestrife – mechanical, biological and chemical – a foliar application of herbicide was selected given the difficulty to access the sites with equipment and for the treatment to be cost-effective. The airboats carried tanks filled with an herbicide mixture, and crew members would return to the boat to refill their four-gallon backpack.
Doan wrote via email that this was the first time the WCC crew treated purple loosestrife.
“Compared to other sites of loosestrife that I have seen in Western Washington, these sites were more infested due to this being the first year they were treated. Other sites we have seen have been treated previously and are being monitored and retreated when necessary,” Doan said.
Treating the purple loosestrife in this section of the Chehalis River will be ongoing.
“This is going to require several years of treatment, and we definitely didn’t get it all,” Davis said. “Next year, I’m hoping that we can get back out there.”
In reflecting upon what was accomplished this year, Sherman said what makes this type of work feel so important is the cascading effects.
“Every place that was once shaded or was once a complex mosaic of native plants, that being reduced [by the purple loosestrife] has impacts [on] temperature, on waterfowl, on habitat complexity for juvenile salmon,” Sherman said. “It’s just all very, very interconnected.”
