ed here from Asia for sale as an ornamental. The fast growing 4- to 12-foot-tall false bamboo perennial with bright green foliage and showy white blooms was an easy sale to homeowners looking for screening from neighbors. But later there were discoveries of uninvited canes coming up in lawns and clumps showing up on nearby properties.

Nothing to worry about? We are sadder, but wiser now.

Not just seeds can germinate and grow, but also cut or broken stems and roots will sprout if left on moist soil, put directly into water, moved by beavers or earth moving equipment, or spread in contaminated landfill material.

Thus, like an invasive malignancy, knotweed has found a way to wet places far upstream on the banks of rivers and creeks to sprout and spread and displace native plants, overrun gravel bars, clog small waterways, create bank erosion and flooding problems and lower the quality of habitat for fish and wildlife. Where knotweed grows, you will not find forested riverbanks crucial to the health of trout and salmon.

In the drainages of the rivers flowing out of the Cascades, including those flowing through our Snoqualmie Valley, there’s a war on to kill it.

Winning the war requires organization and supervision from specialists in invasive control, cooperation from people with knotweed growing on their property and help from volunteers.

The war to rein in Valley rivers’ knotweed infestations began in earnest in the summer of 2006. Under the direction of Monica Walker, knotweed project manager for the King County Noxious Weed Program, great progress is being made on the Middle and South Fork Snoqualmie River Projects. Allocation of funding for Snoqualmie River projects was included in funds secured from the U.S. Fish and Wildlife Service, U.S. Forest Service, Washington State Department of Agriculture Knotweed Project and King County.

This past summer, the previous success on the upper Middle Fork freed crews to begin control in the Three Forks Natural Area, just outside North Bend and upstream from the confluence of the of the river’s three forks. This is the final large knotweed infestation on the Middle Fork.

Surveys last June led to the beginning of control in the upper reaches of the South Fork including about 6.5 acres in Ollalie State Park off Interstate 90, Exit 38. An eager EarthCorps crew of young people did this work.

Downstream, following a knotweed workshop conducted by King County, 17 riverfront homeowners and friends joined together to kill knotweed on the stretch bounded by the Cedar Village and River Bend communities between Cedar Falls and Edgewick roads.

Together, these efforts controlled knotweed over about half a mile along both sides and on one big island in the middle of the river. The volunteers used knotweed stem injection guns provided by Cedar Village homeowner Dave Olson and the Washington State Department of Natural Resources to apply a special herbicide provided by King County and approved for use in aquatic areas.

The hope of all concerned is to see control of knotweed on the South Fork essentially completed all the way to its junction with the Middle Fork within the next two or three years, with ongoing maintenance as needed.

What you can do

Voluntary eradication of small established sites and prevention of new infestations is key to controlling invasive knotweed species. Since knotweed doesn’t give up easily, most control methods usually need to be applied over several years to be successful.

Prevention begins with questioning vendors concerning the invasiveness of offerings you see in nurseries and not buying offending varieties.

Small infestations should be dug up and removed. Remember, plants can re-sprout from creeping rhizomes so be sure to remove the entire root system. Roots should be thrown in the garbage or taken to the transfer station. For larger stands, start by cutting twice a month during the growing season.

Cuttings should be dried out and burned or composted separately from other yard waste, then monitored for re-growth. If the knotweed is on dry land and away from water, herbicides that contain glyphosate such as Roundup can be sprayed on plants in the late summer or early fall. If spraying in the early summer, consider products with the active ingredient triclopyr, including Crossbow and Brush B Gone. This is a good choice in lawn areas as it does not injure most grasses. Don’t spray next to water and pick a day without rain for spraying.

In wetlands and along waterways, attacking full-grown canes with a stem injection gun is the weapon that works. This method nearly eliminates the risk of drift and ground contamination. While labor-intensive and expensive – it kills almost 100 percent of canes, turning thriving clumps to stands of dark brown dead sticks in about three weeks.

For more information, contact the King County Noxious Weed Program at (206) 296-0290 or by e-mail at noxious.weeds@kingcounty.gov. If you are interested in volunteering to work with neighbors in continuing control efforts along the South Fork next summer, call Dave Olson at (425) 888-6046.

Dave Olson is a Cedar Village property owner who has been engaged in battles to eradicate and control noxious plant invasions in the Snoqualmie Valley for the past four years.