By Nancy Henderson
Most people are familiar with the invasive plant Scotch Broom, but fewer know about knotweed, a much more-threatening species.
Knotweed is very aggressive, escaped ornamental that is capable of forming dense stands, crowding out all other vegetation and degrading wildlife habitat. These aggressive invasive plants grow better in their new habitat due to the absence of native predators and diseases that limit their growth in their native Asia.
Knotweed is a herbaceous, perennial tall shrub with bamboo like stems, large green spade or heart-shaped leaves, and small, creamy white to greenish white flowers that grow in plume-like clusters. Knotweed grows in many habitats, but is of most concern adjacent to streams and rivers. The plants are usually 6-12 feet tall. Knotweed grows in dense stands, peaks by July, and goes dormant in winter, with dead brown stems remaining.
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“Unfortunately we are finding more and more patches of knotweed around Steilacoom, and the patches are becoming larger each year, elbowing out native plants,” says Nancy Henderson, Steilacoom Parks and Trails volunteer who is organizing a collaborative effort with the Town and the Pierce Conservation District to eradicate the weed.
Knotweed is extremely difficult to control due to its incredibly extensive root system and sprouting ability. Digging or removing the plant by hand causes plants to send more roots underground and actually increases the infestation size. Special herbicide treatments are the only known effective means of removal.
Many estuaries and riparian areas in Washington State have been significantly impacted by knotweed, which erodes banks and damages habitat for native fish, birds, insects and wild animals. Millions of dollars have been spent to revitalize estuaries and salmon habitat in Washington State. Eradication of knotweed is a major part of that effort.
“The most important piece of this work is public education,” says Henderson. “Identification of infestation sites is first. However, proper removal methods and prevention of further infestations from illegal dumping of yard waste in natural places is also important.”
The WA State Noxious Weed Control Board advises that knotweed must never be placed in yard waste, compost bins, or vacant lots, but rather bagged up and placed in the trash. One inadvertent wheelbarrow full of knotweed can mean years of costly treatments to regain the environmental health of salmon habitats. Prevention is absolutely the most important action to avoid this “biological pollution.”
Thursday, September 12, is the date the Pierce Conservation District will assist with knotweed eradication in Steilacoom. The effective eradication of knotweed requires combined efforts among both public and private land owners. Private property owners who wish to have knotweed eradicated from their property should contact Mark Burlingame, Director of Public Works, at 581-1912.
For more information on knotweed, contact the Pierce Conservation District, 253-845-2973, www.piercecountycd.org.
