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Species
Information
- Japanese
knotweed
- Polygonum
cuspidatum Sieb. & Zucc.
- USDA
Symbol: POCU6
- Oregon
Noxious Weed Designation: B, T
- Pictures
ALERT: PLEASE CALL 1-866-INVADER IF YOU SUSPECT YOU HAVE FOUND THIS SPECIES
Identification:
Perennial; blooms July to October. Grows 4 to 9 ft tall from long creeping rhizomes. Stout stems reddish-brown, nodes slightly swollen. Leaves short stalked, trucate, broadly ovate and 2-6" long by 2-4" wide. Flowers greenish-white to cream in large plume-like clusters at the ends of the stems. Hybrids with giant knotweed are common.
Impacts: Japanese knotweed is a native of Eurasia and was introduced to the U.S. as an ornamental. Plants grow vigorously along roadsides, waste areas, streams and ditch banks and create dense colonies that exclude native vegetation and greatly alter natural tree regeneration. Established populations are extremely persistent and do not respond to mowing/cutting. Large infestations can be eliminated with approved herbicides, but treatments are costly and time consuming. It poses a significant threat in riparian areas, where it disperses during flood events rapidly colonizing scoured shorelines, islands and adjacent forest land.
Biological
Controls: No approved biocontrol agent is currently available.
Oregon
Maps of Japanese Knotweed Distribution
Links:
USDA
Plants Database information on Japanese knotweed
GRIN
Database information on Japanese
knotweed
Oregon Department
of Agriculture information on Japanese
knotweed
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