Japanese Knotweed

Japanese Knotweed Facts and Removal Techniques

 How it was introduced/ migrated

Introduced in late 1800s from East Asia to stabilize streambanks by Philipp Franz Balthasar von Siebold (Shallcross). He went on a 7-year journey studying medicine and collecting plants. He was interested in Japanese plants and bringing Western medicine to Japan. Siebold was a popular botanist who introduced this species as an ornamental. Another use for this plant is erosion control (JSTOR). 


© The Portugal News

How it started to take over the ecosystem

Seeds are papery and spread easily through wind and water (Penn State Extension). They are not too durable but the number of them compensates. Knotweed has rhizomes that form an interconnected network underground (Gillies). Japanese knotweed can re-root itself by having a piece of it breaking off and floated down a stream and colonizing new area (pervasive). There are no predators or diseases and plants cannot compete. Is kept in check in its native range by other plants and animals.

How to remove and include a case study 

The best way to remove knotweed is by eliminating its rhizome system. It is tough because it is all underground. It is expensive since digging up the site is necessary. Cutting is not an option because any shrapnel will re-root itself and the problem. Cutting Knotweed on June 1st reduces the plant height from 6-10ft to 2-4ft (Managing Japanese Knotweed and Giant Knotweed on Roadsides). Direct spraying & injection of herbicides are some of the most effective methods. Overusing herbicides can be detrimental to the ecosystem by introducing toxic chemicals into wetlands. Uprooting runs the risk of regrowth since if there is a small piece left behind, it can recolonize.


© Japanese Knotweed Plus



© Managing Japanese Knotweed and Giant Knotweed on Roadsides

Fun facts & other information

Stems resemble bamboo and grow zigzag. Releases chemicals into the soil which inhibit growth of other plants (allelopathy) (Gilies). Considered an ideal weed since it shares many characteristics; can grow almost everywhere, produces many seeds. Affects species richness. 



Works Cited
Gillies, S., Clements, D. R., & Grenz, J. (2016). Knotweed (Fallopia spp.) Invasion of North America             Utilizes Hybridization, Epigenetics, Seed Dispersal (Unexpectedly), an Arsenal of Physiological             Tactics. Invasive Plant Science and Management, Invasive Plant Science and Management 9(01),         71–80. DOI:10.1614/ipsm-d-15-00039.1

Managing Japanese Knotweed and Giant Knotweed on Roadsides. https://www.forestandwatersolutions.com/uploads/3/6/3/1/3631108/managing_knotweed_part_2.pdf.

“Japanese Knotweed.” Penn State Extension, 4 Feb. 2020, https://extension.psu.edu/japanese knotweed. 

Shallcross, Marie. “Japanese Knotweed a Brief History of an Invasive Weed.” Plews Garden Design, 13 Sept. 2021, https://plewsgardendesign.co.uk/japanese-knotweed-a-brief-history-invasive-weed/.

Siebold, Philipp Franz (Balthasar) Von (1796-1866) on JSTOR. https://plants.jstor.org/stable/10.5555/al.ap.person.bm000007805.

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