Knotweed battle keeps growing

By Brian Mittge
The (Centralia) Chronicle

BRIAN MITTGE / THE (CENTRALIA) CHRONICLE : Kathy Jensen holds a stalk of Japanese knotweed, an aggressive, nonnative plant, at her home in Chehalis.

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Barely six months later, she is a battle-hardened soldier in a war against Japanese knotweed.

She joins a growing statewide battle against the aggressive, nonnative plant.

Jensen growls when the subject of knotweed comes up. She calls it a hostile invading force.

"I swear you can sit there and watch it grow," she said.

Some thickets of knotweed are already 16 feet tall this year, she said.

Knotweed's red segmented stalks resemble bamboo, but it only looks as if it could feed pandas or be made into a fishing pole. The plant actually is a member of the buckwheat family.

Knotweed dies back every winter to red skeletons and quickly becomes brittle when cut down. It grows back with gusto.

Jensen, who once was an organic farmer in Buckley, now uses herbicides to control knotweed.

"It galls me to have to use chemicals, but it's the only way we can control it," she said. "We want our property nice, and this is such an invasive and fast-growing weed."

Knotweed has been looming on the radar screen recently for people who worry about nonnative plants such as English ivy, Himalayan blackberry and the lake-choking Brazilian elodea once sold for aquariums.
 
Like those alien plants, knotweed has a knack for dominating almost any place it touches down.

Though knotweed plants thrive in summer, they leave shorelines bare and open to erosion when they die back in the winter.

Knotweed, introduced from Japan and Asia, continues to spread and is on track to become one of the dominant plants on the planet, experts say.

In its native habitat, knotweed colonizes bare volcanic slopes, according to Brad Archbold, knotweed program coordinator with the state Department of Agriculture.

"In Washington, these knotweed species lack any natural predators and can invade large areas of important habitat," crowding out native willows, cottonwoods and conifers such as Douglas fir, he said in a letter to landowners.

In England, Archbold said, some river corridors are nothing but thick, nearly impenetrable walls of knotweed.

Introduced to Great Britain as an ornamental plant in 1825, knotweed was brought to America in the late 1800s.

It can grow almost anywhere, but it thrives along riverbanks and streams.

The Department of Agriculture has given out grants this year to attack knotweed in entire river systems, from the top down. In Lewis County, the focus is on the upper Cowlitz River south of Mount Rainier.

Eradicating the weed entirely from an area would take a decade or more, if it's even possible, said Sara Carter, a weed-management specialist with the Lewis County Noxious Weed Control Board.

Still, many landowners are signing on for the program.

"So far, there's been good response from people anxious to do some control work," said Bill Wamsley, head of the county's weed board.

A property near the Cowlitz River in Randle has a patch of giant knotweed, a related species that can grow 20 feet tall each year.

"It's this crazy-looking type of plant with these leaves that are 18 inches long," Carter said.

The plant is flowering this time of year with delicate yellow-white strings of flowers dusted across its large oval- or heart-shaped leaves.

Until now, the plant has mainly spread when pieces are moved around by humans, floods or in contaminated soil.

"Root and stem fragments as small as one inch can produce a new plant," according to a guide from the Nature Conservancy. "As a result, even one patch can produce dozens of new populations."

The plant has tough underground rhizomes that can spread 25 feet to each side of the above-ground plant.

"It has as much biomass underground as above," Carter said.

Digging breaks up that root system and encourages the plant to spread.

So does mowing or weed-whacking it, unless all the pieces are allowed to dry completely, or are buried more than 10 feet down.

Simply cutting knotweed and dumping it in a compost pile is like carefully planting it in a new location, Carter said.

The most effective method of control, experts say, is applying a glyphosphate chemical such as Roundup. Around water, a chemical called AquaMaster is the best bet.

This is the time of year to use herbicides on knotweed because the plant is flowering and preparing to send energy back down to its roots.