California Invasive Plant Council

Fallopia japonica

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*

Cal-IPC Assessment

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 Reports

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.

• 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)

Other Fallopia japonica Information

• CalPhotos - Images of plants taken mostly in California.
• Calflora - See the distribution of this species on Calflora's map of California.
• CalWeedMapper - Distribution information with ability to determine regional priorities.
• Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
• CDFA - California official noxious weeds.
• USDA PLANTS Database - Federal database with information on identification and distribution, and links to websites in individual states.
• EDDMapS - North American distribution based on Early Detection and Distribution Mapping System.