Synonyms: Polygonum cuspidatum; Reynoutria japonica, Fallopia baldschuanica
Common names: Japanese knotweed; Mexican bamboo
Fallopia japonica (=Polygonum cuspidatum) (Japanese knotweed) is a perennial forb/herb (family Polygonaceae ). Plants grow vigorously and create dense colonies that exclude other vegetation. Established colonies are extremely difficult to eradicate. It inhabits disturbed moist sites, roadsides, riparian and wetland areas. Plants typically grow in open, sunny areas on moist soils in cool temperate climates. There is very little of this species in California, but it is spreading rapidly in the Northwest and has been a major problem in the southern and northern US, as well as Europe.Cal-IPC Rating: Moderate — Alert?
CDFA Rating: A*?
Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.
Species ID Card
Invasive Species ID Card - To support field identification of early detection species, Cal-IPC has designed a set of Species ID cards that can be downloaded, printed double-sided, and trimmed to size.
Special ReportsResources for ID and potential "look-alikes" from UC Agriculture and Natural Resources, with the Marin Knotweed Action Team
Weed Management Notes
- Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.
Cal-IPC Newsletter Articles
- Knocking out knotweed in Marin County. Dirkse, Anna. Vol 28, Issue 2
- The cost of inaction: An example from the Toutle River. Cal-IPC. Vol 27, Issue 3
- Eradicating knotweeds and other new invaders on California’s North Coast. Eberwein, Amy. Vol 24, Issue 3
- Working on weeds in the eastern US. Meyer, Tanya. Vol 22, Issue 1
- Tracking eradication progress . Guise, Vince. Vol 21, Issue 3
- Jepson Manual 2nd ed. invasive plant name changes. Brusati, Elizabeth. Vol 20, Issue 2
- Chasing weeds from Maine to California. Stack, Lois Berg. Vol 16, Issue 4
- Japanese knotweed (Polygonum cuspidatum) and other knotweeds. Brusati, Elizabeth. Vol 13, Issue 1
Cal-IPC Symposium Presentations
Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.
- North coast invasive weeds – early detection rapid response eradication project. Reynolds, Candace (2023)
- Regional EDRR with Bay Area WMAs. Johnson, Doug; Valentine, Nicole (2022)
- North Coast invasive weeds: Early detection rapid response eradication project. Ferson, Susannah; Avila-Martinez, Carla (2021)
- The role of public gardens as sentinels of plant invasion. Culley, Theresa; Dreisilker, Kurt; Ryan, Clair; Landel, Hans; Cavallin, Nadia; Arcate Schuler, Jessica; Shultz, Brittany; Gettig, Roger; Havens, Kayri (2020)
- 2019 Weed Alerts. Burger, Jutta; Price, Bob (2019)
- Communicating the threat of Japanese knotweed (Fallopia japonica) to private landowners along San Geronimo Creek. Dirkse, Anna (2019)
- Partnerships lifeline: early detection and eradication of Japanese knotweed across boundaries. Simpson, Bobbi (2018)
- 2003 Cal-IPC red alert! New invasions, recent expansions, and a few others to be on the look-out For…. Tu, Mandy; Randall, John M. (2003)
Other Fallopia japonica Information
- CalPhotos - Images of plants taken mostly in California.
- Calflora - Distribution map and records of this species in California.
- CalWeedMapper - Distribution map of this species in California with ability to determine regional priorities.
- EDDMapS - Distribution of this species in North America.
- Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
- USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.