MAPLE VALLEY — The banks of the Cedar River are lush and verdant. A patchwork carpet of soft green biodiversity. Just within a couple of yards of the water’s edge, the species are abundant, the nomenclature mellifluous: buttercup, foxglove, leopard’s bane, nipplewort, forget-me-not, large-leaf aven, fringe cup, sticky willy.

But there is an intruder in the midst.

A swath of bright-green, veined leaves, kidney-shaped around a central stem, with rounded, saw-toothed edges. It’s early in the season, so they’re still short. But they’ve spread broadly.

This is garlic mustard, a Washington state Class A noxious weed. Left to its own devices, it will take over this riverbank. It will spread like wildfire. It will win the battle for soil, for nutrients, for light, for space. It will exude phytochemicals, disrupting the relationship between the roots of other plants and beneficial fungi in the soil, making it even more difficult for other plants to grow.

Its seeds, which can survive for 10 years, will spread farther, carried by foot, by wind, by floodwaters.

It will choke out the harmonious ecosystem that thrives here.

Washington has 38 species of Class A noxious weeds — invasive plant species that have gained a toehold in the state and, if allowed to spread, would threaten local crops, ecosystems and habitats. Washington has laws to control noxious weeds that were passed before Washington became a state. All but one county has its own noxious weed control board to monitor for new weeds and help limit their spread.

King County spends around $4 million a year trying to control these invasive plants as part of the King County Noxious Weed Control Program.


Farmers, orchards and ranchers spend millions more trying to control noxious weeds, and they lose millions in potential production.

It is a never-ending battle, not quite futile, but one where victories are usually temporary and unsung, while losses are permanent and showcase themselves on every available inch of soil across the state.

“Unkillable ghosts”

The story of Washington’s first declared noxious weed is emblematic of the difficulty in controlling their spread.

Canada thistle, a spindly purple-flowered weed native to southeastern Europe, likely came to North America in the 1600s in a batch of contaminated seed or in the ballast of a ship.

It spread quickly. Its roots can spread up to 12 feet a year, each plant can produce up to 5,000 seeds and seeds can survive for 22 years. It creates dense clusters that crowd out native plants and crops.

In 1881, Washington’s territorial government passed its first noxious weed law, to try to control the spread of Canada thistle.


Today, 140 years later, Canada thistle is a Class C noxious weed in Washington. The lower class does not mean it spreads slower or is less harmful than Class A or Class B weeds. Rather, it basically means the battle has been lost.

All noxious weeds are invasive and harmful. Class A weeds are still very limited in their spread, so to try to keep it that way, they are given highest priority. Counties and private landowners are required by law to eradicate Class A weeds. Class B weeds are widespread in some parts of the state, but still limited in others. Counties try to contain them. Class C weeds are everywhere.

“It’s counterintuitive, you see, ‘Oh my gosh they’re everywhere, we need to do something,'” said Janet Spingath, the Western Washington representative on the state Noxious Weed Control Board. “We’d love to eradicate those, but it’s just not possible.”

The board updates the state’s list of noxious weeds each year, with suggestions from the public, review by scientists, debate and votes. There are currently 155 state-designated noxious weeds across the three classes.

Some are tasty. The blackberry bushes clogging the alley with an impenetrable thicket of thorns? Noxious weed.

Some are pretty. The scotch broom, lighting up highway hillsides with blazing yellow blooms? Noxious weed.


Some are stately. The English Ivy elegantly but ominously engulfing that brick house? Noxious weed.

Some conjure images of vernal tranquility. Fragrant water lilies, white daisy, common fennel. Noxious weed, noxious weed, noxious weed.

All are invasive. All pose an economic or environmental hazard if allowed to spread too widely.

Scotch broom, with its vivid sweet pea-shaped yellow flowers, forms dense stands of brush. It outcompetes saplings and can be poisonous to livestock. In 2017, the state estimated it as the second-costliest noxious weed in Washington, with the potential to cause $143 million in annual losses for agriculture and timber if allowed to spread unabated. It is a Class B weed and is widespread throughout Western Washington.

Each plant produces thousands of seeds and each seed can remain viable for decades. Once it’s got a foothold, it’s awfully tough to displace.

“I tell people, if you’ve got it, your kids will have it,” said Sayward Glise, a noxious weed specialist for King County.


Washington weed warriors vanquish Scotch broom

The noxious weed estimated to be costliest, with a potential for $149 million in annual losses, is rush skeletonweed, a wiry, branching plant with little yellow daisy flowers. It is widespread in eastern Washington, where it threatens wheat, potato and hay crops.

But there are success stories too.

Kudzu, the so-called “vine that ate the South,” was discovered in Clark County in 2005. This was a five-alarm fire in the noxious weed community.

“Everyone was like, ‘Noooooo,'” Glise said.

Kudzu can grow up to a foot a day, notoriously engulfing parked cars and pulling down power lines. And, as the climate warms, Washington will only become more hospitable.

“Green, mindless, unkillable ghosts,” the poet James Dickey wrote of the vine. “In Georgia, the legend says / That you must close your windows / At night to keep it out of the house.”

But in Clark County, it was quickly controlled with herbicides, eradicated and hasn’t been reported in Washington since.

It remains a Class A noxious weed.

“If something’s just at one location, it’s just showing up, we’re going to make that the top priority to get at because we probably have a good chance of not letting it spread in the state,” Spingath said.


It’s Sisyphean

For Glise, noxious weeds have a way of seeping into even her non-work hours.

On a trip to New York, she went for a walk in Brooklyn’s Prospect Park, the 150-year-old Olmsted-designed urban oasis. Uh oh, she thought to herself, there’s a patch of garlic mustard.

Years ago, a friend told her he was thinking of honeymooning at a spot on the Raging River, a tributary of the Snoqualmie.

“I was like, ‘Don’t go there, there’s knotweed everywhere,'” she said.

Glise leads a nine-person King County riparian team, scanning the banks of the Lower Cedar, Upper Snoqualmie, Green, Duwamish and the South Fork of the Skykomish rivers.

They fan out in a search-and-rescue-style grid, eyes down, scanning the natural mosaic for leaves that don’t belong. On these King County riverbanks, they’re mostly looking for garlic mustard (in the spring and early summer) and Japanese knotweed (later in the season).


They carry spray bottles of imazapyr, a bright blue chemical herbicide. Imazapyr works by blocking production of a necessary plant enzyme, one that’s not found in animals. It’s thought to be relatively low risk. Still, it’s an herbicide. The team has to weigh the risks of using it versus the harm from allowing garlic mustard to proliferate or the potential erosion caused by digging up vast sections of riverbank.

“Herbicide can be the gentlest tool in the toolkit,” Glise said. “We’re trying to disturb the environment as little as possible.”

If the plants are still young, they’ll get an herbicide spritz; if they’re bolting (producing seeds) they have to be pulled by hand and stuffed in a garbage bag.

The team will map where they’ve been and what they’ve found in smartphone apps, both so they don’t duplicate their efforts and so they’re able to check back on problem spots in future years.

A mile or so down river from where the team is working, Glise points to the opposite bank, a bucolic scene: willows, a rocky beach, gently flowing water.

Ten years ago, it was all knotweed.

The team will cover 150 river miles this year, arriving at some tough-to-reach spots by inflatable kayak.


Since the weed control program started looking for garlic mustard in 2000, the total acreage of the weed has been reduced by 64%, according to the county’s most recent annual report.

But it’s Sisyphean.

In 2010, there were 242 active garlic mustard sites in the county. In 2020 there were 590.

“People are always being like, ‘When will the knotweed be gone?'” Glise said. “‘When will the garlic mustard be gone?'” she trails off. She shrugs her shoulders.