Physical Description
Giant knotweed regularly grows to heights greater than 10 feet, with an upper limit of about 18 feet. The large oval to elliptic-shaped leaves help to easily distinguish it from Japanese Knotweed. However, giant knotweed readily hybridizes with Japanese knotweed to produce the hard-to-distinguish Bohemian knotweed.
- Large (12 to 18 inches) oval to elliptic leaf shape with a heart-shaped base
- 6 to 18 feet tall
- Light green segmented stems that are hollow, similar to bamboo stems, with a red papery sheath located between stem segments (no red spots on stems like Japanese or some Bohemian knotweeds)
- Long flexible hairs on leaves
- The middle leaf vein is rounded in cross section
- Cream colored, sweet-smelling, linear flower bunches at each leaf
Where is it located in Lincoln County?
Giant knotweed is the second most abundant knotweed species in Lincoln County. It is predominantly found in the upper Salmon River basin, Middle Yaquina River (above and below Eddyville), and in Elkhorn Creek (tributary to Beaver Creek).
Control Efforts
Giant knotweed infestations take several years of treatment to control, and the most effective method is repeated herbicide application. Contacting a natural resource professional as early as possible is integral to knotweed control. If you see giant knotweed, contact the Oregon Invasives Hotline as well as the Lincoln Soil and Water Conservation District (LSWCD) by phone at (541) 265-2653 or email Lincoln SWCD.
