Editing Reynoutria japonica

{{Short description|Flowering plant (Japanese knotweed)}}
{{Redirect|Donkey rhubarb|the EP by Aphex Twin|Donkey Rhubarb (EP)}}
{{Speciesbox
|image = Reynoutria japonica in Brastad 1.jpg
|taxon = Reynoutria japonica
|authority = [[Martinus Houttuyn|Houtt.]]<ref name=POWO_435655-1/>
|synonyms_ref = <ref name=POWO_435655-1/>
|synonyms =
  {{Species list
  |Fallopia compacta|(Hook.f.) G.H.Loos & P.Keil
  |Fallopia japonica|(Houtt.) Ronse Decr.
  |Pleuropterus cuspidatus|(Siebold & Zucc.) H.Gross
  |Pleuropterus zuccarinii|(Small) Small
  |Polygonum compactum|Hook.f.
  |Polygonum cuspidatum|Siebold & Zucc.
  |Polygonum hachidyoense|Makino
  |Polygonum reynoutria|Makino
  |Polygonum zuccarinii|Small
  |Reynoutria hachidyoensis|(Makino) Nakai
  |Reynoutria hachijoensis|Nakai ex Jôtani
  |Reynoutria hastata|Nakai ex Ui
  |Reynoutria henryi|Nakai
  |Reynoutria uzenensis|(Honda) Honda
  |Reynoutria yabeana|Honda
  |Tiniaria japonica|(Houtt.) Hedberg
  }}
}}

'''''Reynoutria japonica''''', synonyms '''''Fallopia japonica''''' and '''''Polygonum cuspidatum''''', is a [[species]] of [[herbaceous]] [[perennial plant]] in the knotweed and buckwheat family [[Polygonaceae]].<ref name=POWO_435655-1/><ref name="cabi">{{cite web |url=https://www.cabi.org/isc/datasheet/23875 |title=Fallopia japonica (Japanese knotweed) |last=Shaw |first=D |date=19 July 2013 |website=CABI |publisher=CAB International |access-date=10 May 2022 }}</ref> Common names include '''Japanese knotweed'''<ref name="cabi"/> and '''Asian knotweed'''.<ref>{{Cite book|url=http://www.forest.go.kr/kna/special/download/English_Names_for_Korean_Native_Plants.pdf|title=English Names for Korean Native Plants|publisher=[[Korea National Arboretum]]|year=2015|isbn=978-89-97450-98-5|location=Pocheon|pages=358|access-date=4 January 2017|via=[[Korea Forest Service]]|url-status=dead|archive-url=https://web.archive.org/web/20170525105020/http://www.forest.go.kr/kna/special/download/English_Names_for_Korean_Native_Plants.pdf|archive-date=25 May 2017}}</ref> It is native to [[East Asia]] in [[Japan]], [[China]] and [[Korea]]. In [[North America]] and [[Europe]], the species has successfully established itself in numerous habitats, and is classified as a pest and [[invasive species]] in several countries.<ref name=cabi/><ref name=cabi-inv/><ref name="ontario">{{cite web|url=http://www.invadingspecies.com/invaders/plants-terrestrial/japanese-knotweed/|title=Japanese Knotweed, ''Reynoutria japonica'' var. ''japonica''|publisher=Invading Species Awareness Program, Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario Canada|date=2012|access-date=2 August 2017|archive-url=https://web.archive.org/web/20170808010927/http://www.invadingspecies.com/invaders/plants-terrestrial/japanese-knotweed/|archive-date=8 August 2017|url-status=dead}}</ref> The plant is popular with beekeepers, and its young stems are edible, making it an increasingly popular [[foraging|foraged]] vegetable with a flavour described as [[lemon]]y [[rhubarb]].<ref>{{Cite web |last=Seal |first=Nic |date=2023-04-04 |title=Is Japanese knotweed safe to eat? |url=https://www.environetuk.com/blog/is-japanese-knotweed-safe-to-eat |access-date=2024-01-06 |website=Japanese Knotweed and Invasive Plant Specialists {{!}} Environet UK |language=en-GB}}</ref>

==Description==
The [[flower]]s are small, cream or white, produced in erect [[raceme]]s {{convert|6|–|15|cm|in|frac=2|abbr=on}} long in late summer and early autumn. Japanese knotweed has hollow stems with distinct raised [[node (botany)|node]]s that give it the appearance of [[bamboo]], though it is not related. While stems may reach a maximum height of {{convert|3|–|4|m|ft|0|abbr=on}} each growing season, it is typical to see much smaller plants in places where they sprout through cracks in the pavement or are repeatedly cut down. The [[leaf|leaves]] are broad oval with a truncated base, {{convert|7|–|14|cm|in|frac=2|abbr=on}} long and {{convert|5|–|12|cm|in|frac=2|abbr=on}} broad,<ref>{{cite web|url=http://www.rhs.org.uk/advice/profile?PID=218 |title=Japanese knotweed |publisher=Royal Horticultural Society |access-date=6 June 2014}}</ref> with an entire margin. New leaves of ''Reynoutria japonica'' are dark red and {{convert|1|to|4|cm|in|frac=2|abbr=on}} long; young leaves are green and rolled back with dark red veins; leaves are green and shaped like a heart flattened at the base, or a shield, and are usually around {{convert|12|cm|in|0|abbr=on}} long.

Mature ''R.{{nbsp}}japonica'' forms {{convert|2|to|3|m|ft|frac=2|adj=mid|-tall}}, dense thickets.  Leaves shoot from the stem nodes alternately in a zigzag pattern. Plants that are immature or affected by mowing and other restrictions have much thinner and shorter stems than mature stands, and are not hollow.<ref>{{cite web |url=http://www.phlorum.com/services/japanese-knotweed/domestic-knotweed-removal/knotweed-identification/ |title=How To Identify Japanese Knotweed, Knotweed Identification Card & Pictures |newspaper=Phlorum.com |access-date= 26 June 2017}}</ref>

<gallery widths="200px" heights="160px">
File:WEEDS054.jpg|Dead stems from previous years [[marcescence|remain in place]] as new growth appears.
File:Caersws headg row1.jpg|A hedgerow made up of [[rose]]s and Japanese knotweed
File:Knotweed054.jpg|Erect inflorescence
</gallery>

==Identification==
Identification of Japanese knotweed may be confused with other plants suspected of being knotweed, due often to the similar appearance of leaves and stems. [[Dogwood]], [[lilac]], [[houttuynia]] (''Houttuynia cordata''), ornamental [[bistort]]s such as red bistort (''[[Persicaria amplexicaulis]])'', lesser knotweed (''[[Koenigia campanulata]]''), Himalayan balsam (''[[Impatiens glandulifera]]''), broad-leaved dock (''[[Rumex obtusifolius]]''), bindweed (''[[Convolvulus arvensis]]''), [[bamboo]], Himalayan honeysuckle (''[[Leycesteria formosa]]''), and Russian vine (''[[Fallopia baldschuanica]]'') have been suspected of being ''Reynoutria japonica''.<ref>{{cite web |url=http://www.phlorum.com/services/japanese-knotweed/plants-that-look-like-japanese-knotweed/ |title=Plants That Look Similar To Japanese Knotweed: Plants Mistaken For Knotweed |newspaper=Phlorum.com |access-date= 26 June 2017}}</ref>

== Uses ==
[[File:Variegated Japanese Knotweed Foliage.jpg|thumb|A variegated variety of Japanese knotweed, used as a landscape plant]]

Japanese knotweed flowers are valued by some beekeepers as an important source of nectar for honeybees, at a time of year when little else is flowering. Japanese knotweed yields a [[monofloral honey]], usually called ''bamboo honey'' by northeastern U.S. [[beekeeper]]s, like a mild-flavored version of [[buckwheat]] honey (a related plant also in the Polygonaceae).<ref name="bobisetal">{{cite journal |last1=Bobis |first1=Otilia |last2=Dezmirean |first2=Daniel Severus |last3=Bonta |first3=Victorița |last4=Moise |first4=Adela |last5=Pasca |first5=Claudia |last6=Domokos |first6=Timea Erzsebet |last7=Urcan |first7=Adriana Cristina |title=Japanese Knotweed (Fallopia japonica): Landscape Invasive Plant versus High Quality Honey Source |journal=Scientific Papers. Series D. Animal Science |date=2019 |volume=62 |page=231-235 |url=https://www.animalsciencejournal.usamv.ro/pdf/2019/issue_1/Art34.pdf |access-date=2 November 2024}}</ref>

The young stems are edible as a spring [[vegetable]], with a flavour similar to [[rhubarb]].<ref>{{Cite book|last1=Elias|first1=Thomas S.|url=https://www.worldcat.org/oclc/244766414|title=Edible Wild Plants: A North American Field Guide to Over 200 Natural Foods|last2=Dykeman|first2=Peter A.|publisher=[[Sterling Publishing|Sterling]]|year=2009|isbn=978-1-4027-6715-9|location=New York|pages=99|oclc=244766414|orig-year=1982}}</ref> In some locations, semi-cultivating Japanese knotweed for food has been used as a means of controlling knotweed populations that invade sensitive wetland areas and drive out the native vegetation.<ref>{{cite web|url=http://www.newtritionink.de |title=Pilot project of Bionic Knotweed Control in Wiesbaden, Germany |publisher=Newtritionink.de |access-date=2014-06-30}}</ref> [[#In Japan|It is eaten in Japan]] as ''[[sansai]]'' or wild foraged vegetable. In Europe, young shoots have been used in restaurant cuisine.<ref>{{Cite news |last=Morrissy-Swan |first=Tomé |date=2023-05-27 |title=Squirrel haggis and Japanese knotweed reach UK menus as invasive species trend grows |language=en-GB |work=The Observer |url=https://www.theguardian.com/food/2023/may/27/squirrel-haggis-and-japanese-knotweed-reach-uk-menus-as-invasive-species-trend-grows |access-date=2023-05-27 |issn=0029-7712}}</ref>

Knotweed can grow up to 30&nbsp;cm per day, hence it is a fast-growing vegetable tolerant of poor quality soils.<ref>{{Cite journal |last1=Cucu |first1=Alexandra-Antonia |last2=Baci |first2=Gabriela-Maria |last3=Dezsi |first3=Ştefan |last4=Nap |first4=Mircea-Emil |last5=Beteg |first5=Florin Ioan |last6=Bonta |first6=Victoriţa |last7=Bobiş |first7=Otilia |last8=Caprio |first8=Emilio |last9=Dezmirean |first9=Daniel Severus|display-authors=3 |date=2021-11-29 |title=New Approaches on Japanese Knotweed (''Fallopia japonica'') Bioactive Compounds and Their Potential of Pharmacological and Beekeeping Activities: Challenges and Future Directions |journal=Plants |volume=10 |issue=12 |pages=2621 |doi=10.3390/plants10122621|doi-access=free |issn=2223-7747 |pmc=8705504 |pmid=34961091}}</ref> Because knotweed is resistant to over-harvesting, it is more often foraged than cultivated as a vegetable. The plant can be eaten raw or cooked.<ref>{{Cite web |last=Preston |first=Marguerite |date=2016-05-31 |title=Meet the Massively Destructive Garden Weed That 'Tastes Like Rain' |url=https://www.bonappetit.com/test-kitchen/ingredients/article/japanese-knotweed-recipes |access-date=2024-01-06 |website=Bon Appétit |language=en-US}}</ref>

Ground-feeding songbirds and gamebirds also eat the seeds.<ref>{{cite book |last1=Niering |first1=William A. |author-link1=William Niering| last2=Olmstead |first2=Nancy C. |title=The Audubon Society Field Guide to North American Wildflowers, Eastern Region |year=1985 |orig-year=1979|publisher=Knopf |isbn=0-394-50432-1 |page=706}}</ref>

Rhizome of ''R. japonica'' is the source of [[lactoperoxidase]] peroxidation cycle substrates, which can act as activators and inhibitors of the antimicrobial properties of that system.<ref>{{Cite journal |last1=Magacz |first1=Marcin |last2=Oszajca |first2=Maria |last3=Nawrot-Hadzik |first3=Izabela |last4=Drożdż |first4=Ryszard |last5=Jurczak |first5=Anna |last6=Hadzik |first6=Jakub |last7=Smakosz |first7=Aleksander |last8=Krzyściak |first8=Wirginia |date=2021 |title=Phenolic Compounds of Reynoutria sp. as Modulators of Oral Cavity Lactoperoxidase System |journal=Antioxidants |language=en |volume=10 |issue=5 |pages=676 |doi=10.3390/antiox10050676 |doi-access=free |issn=2076-3921 |pmc=8146912 |pmid=33926051}}</ref>

===In Japan===
[[File:Reynoutria japonica 15-p.bot-polygo.cuspi-23.jpg|thumb|Japanese knotweed shoots, before cooking]]
It grows widely throughout Japan and is foraged as a wild edible vegetable (''[[sansai]]''), though not in sufficient quantities to be included in statistics.<ref name=maff>{{cite web|year=2004|title= 山菜関係資料 - 山菜文化産業懇話会報告書|url=http://www.rinya.maff.go.jp/puresu/h16-12gatu/1203sansai.htm|trans-title=Wild vegetable related document - Wakami culture industry conference report|publisher=Forestry Agency}}</ref> They are called by such regional names as ''tonkiba'' ([[Yamagata Prefecture|Yamagata]]),<ref name=maff/> ''itazuiko'' ([[Nagano Prefecture|Nagano]], [[Mie Prefecture|Mie]]),<ref name=maff/> ''itazura'' ([[Gifu Prefecture|Gifu]], [[Toyama Prefecture|Toyama]], [[Nara Prefecture|Nara]], [[Wakayama Prefecture|Wakayama]], [[Kagawa Prefecture|Kagawa]]),<ref name=maff/> ''gonpachi'' ([[Shizuoka Prefecture|Shizuoka]], Nara, Mie, Wakayama),<ref name=maff/> ''sashi'' ([[Akita Prefecture|Akita]], Yamagata),<ref name=maff/> ''jajappo'' ([[Shimane Prefecture|Shimane]], [[Tottori Prefecture|Tottori]], Okayama),<ref name=maff/> ''sukanpo'' (many areas).

Young leaves and shoots, which look like asparagus, are used. They are extremely sour; the fibrous outer skin must be peeled, soaked in water for half a day raw or after parboiling, before being cooked.

==Invasive species==
This species is listed by the [[World Conservation Union]] as one of the [[List of globally invasive species|world's worst invasive species]].<ref>{{cite web |vauthors=Lowe S, Browne M, Boudjelas S, De Poorter M |url=http://www.issg.org/pdf/publications/worst_100/english_100_worst.pdf |title=100 of the World's Worst Invasive Alien Species: A Selection from the Global Invasive Species Database |publisher=The Invasive Species Specialist Group, a Specialist Group of the Species Survival Commission of the World Conservation Union |page=6 |date=1 December 2000 |access-date=4 January 2017 |archive-date=22 December 2018 |archive-url=https://web.archive.org/web/20181222193550/http://issg.org/pdf/publications/worst_100/english_100_worst.pdf |url-status=dead }}</ref>

It is a frequent colonizer of [[temperate]] [[riparian]] [[ecosystem]]s, roadsides, and waste places. It forms thick, dense colonies that completely crowd out any other herbaceous species and is now considered one of the worst invasive exotics in parts of the eastern United States. The success of the species has been partially attributed to its tolerance of a very wide range of conditions, including drought,<ref>{{cite journal |last1=Walls |first1=R |date=2010 |title=Hybridization and Plasticity Contribute to Divergence Among Coastal and Wetland Populations of Invasive Hybrid Japanese Knotweed s.l. (Fallopia spp.) |url=https://link.springer.com/article/10.1007/s12237-009-9190-8 |journal=Estuaries and Coasts |volume=33 |issue=4 |pages=902–918 |doi=10.1007/s12237-009-9190-8 |bibcode=2010EstCo..33..902W |s2cid=84481038 |access-date=10 May 2022}}</ref> different soil types,<ref name=cabi/> variable soil pH,<ref>{{cite web |url=http://www.extension.uidaho.edu/publishing/pdf/pnw/pnw0610.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.extension.uidaho.edu/publishing/pdf/pnw/pnw0610.pdf |archive-date=2022-10-09 |url-status=live |title=Knotweed shrubs: identification, biology, and management |last1=Prather |first1=T |last2=Miller |first2=T |last3=Robins |first3=S |publisher=Pacific Northwest Extension, University of Idaho |date=2009 |access-date=10 May 2022}}</ref> and high salinity.<ref>{{cite journal |last1=Richards |first1=C |last2=Walls |first2=R |last3=Bailey |first3=J |last4=Parameswaran |first4=R |last5=George |first5=T |last6=Pigliucci |first6=M |date=2008 |title=Plasticity in salt tolerance traits allows for invasion of novel habitat by Japanese knotweed s. l. (Fallopia japonica and F.×bohemica, Polygonaceae) |url=https://bsapubs.onlinelibrary.wiley.com/doi/abs/10.3732/ajb.2007364 |journal=American Journal of Botany |volume=95 |issue=8 |pages=931–942 |doi=10.3732/ajb.2007364 |pmid=21632416 |access-date=10 May 2022 |archive-date=10 May 2022 |archive-url=https://web.archive.org/web/20220510133425/https://bsapubs.onlinelibrary.wiley.com/doi/abs/10.3732/ajb.2007364 |url-status=dead }}</ref> Its [[rhizomes]] can survive temperatures of {{convert|-35|°C|°F|sigfig=2}} and can extend {{convert|7|m|ft|0}} horizontally and {{convert|3|m|ft|0}} deep, making removal by excavation extremely difficult. The plant is also resilient in response to cutting, vigorously resprouting from the roots.<ref>Gover, Art, Jon Johnson, and Larry Kuhns. "Managing Japanese knotweed and giant knotweed on roadsides." Roadside Vegetation Management Factsheet 5 (2005) [https://www.forestandwatersolutions.com/uploads/3/6/3/1/3631108/managing_knotweed_part_2.pdf]</ref>

===Impact===
[[File:Fallopia overgrows train.jpg|thumb|This antique locomotive at [[Beekbergen]], Netherlands, is overgrown by knotweed. A few years before, it was free of knotweed.]]
Japanese knotweed has a strong and extensive root system that can penetrate through the cracks of hard surfaces such as concrete, asphalt, and brick. As the plant grows, it can cause significant damage to building foundations, walls, and drainage systems, which can be very costly to repair. Its invasive roots can also damage concrete foundations, buildings, roads, paving, retaining walls, and architectural sites. Additionally, the plant's dense growth can impede water flow, increasing the risk of flooding by reducing the capacity of flood channels to carry water.<ref>{{cite web | url =https://naturalresources.wales/guidance-and-advice/environmental-topics/wildlife-and-biodiversity/japanese-knotweed-what-you-need-to-know/?lang=en | title =Japanese knotweed: what you need to know  | language=en-GB | date = 23 December 2023 | publisher = Natural Resources Wales| access-date = 3 June 2024}}</ref>

Recent reporting suggests that Japanese knotweed is not nearly as destructive to structures as once thought. Damage appears to only occur at or near areas that were already compromised.<ref>{{Cite news |last=Subramanian |first=Samanth |date=2023-05-16 |title=The war on Japanese knotweed |language=en-GB |work=The Guardian |url=https://www.theguardian.com/environment/2023/may/16/the-war-on-japanese-knotweed |access-date=2023-05-16 |issn=0261-3077}}</ref>

Japanese knotweed shades out other [[vegetation]], grows over buildings and other structures, encourages fire, and damages paved surfaces.<ref name="UMN-Ext-gard">{{cite web | title=Japanese knotweed, a major noxious weed | website=[[University of Minnesota Extension]] | date=2020-10-06 | url=http://extension.umn.edu/yard-and-garden-news/japanese-knotweed | access-date=2021-05-17 | archive-date=2021-05-17 | archive-url=https://web.archive.org/web/20210517163927/https://extension.umn.edu/yard-and-garden-news/japanese-knotweed | url-status=dead }}</ref>

== Control ==
Japanese knotweed has a large underground network of roots (rhizomes). To eradicate the plant the roots need to be killed. All above-ground portions of the plant need to be controlled repeatedly for several years in order to weaken and kill the entire patch. Picking the right herbicide is essential, as it must travel through the plant and into the root system below. But also more ecologically friendly means are being tested as an alternative to chemical treatments.

===Chemical===
[[File:Knotweed.jpg|thumb|right|250px|Detail of the stalk]]
[[File:Japanese knotweed.jpg|thumb|In spring]]
The abundance of the plant can be significantly reduced by applying [[glyphosate]], [[imazapyr]], a combination of both, or by cutting all visible stalks and filling the stems with glyphosate. However, these methods have not been proven to provide reliable long-term results in eliminating the treated population.<ref name=cabi/>

===Mechanical===
Digging up the rhizomes is a common solution where the land is to be developed, as this is quicker than the use of herbicides, but safe disposal of the plant material without spreading it is difficult; knotweed is classed as controlled waste in the UK, and disposal is regulated by law. Digging up the roots is also very labour-intensive and not always effective. The roots can extend up to {{convert|10|ft|m|abbr=off|order=flip|0}} deep, and leaving even just a few centimetres (inches) of root behind will result in the plant quickly growing back.

Covering the affected patch of ground with a non-translucent material can be an effective follow-up strategy. However, the trimmed stems of the plant can be razor sharp and are able to pierce through most materials. Covering with non-flexible materials such as concrete slabs has to be done meticulously and without leaving even the smallest splits. The slightest opening can be enough for the plant to grow back.

[[Soil steam sterilization]] involves injecting steam into contaminated soil in order to kill subterranean plant parts.<ref>{{cite web|publisher=Soil Steaming and Steam Boiler Blog|url=http://www.soil-steaming-steam-boiler-blog.com/2009/10/das-regierungsprasidium-freiburg-bekampft-das-eingeschleppte-wildkraut-japan-knoterich-mit-heisem-dampf|date=3 October 2009|title=THE REGIONAL BOARD OF FREIBURG FIGHTS JAPANESE KNOTWEED, AN INVASIVE NEOPHYTE, WITH HOT STEAM|access-date=1 January 2010|archive-url=https://web.archive.org/web/20110716103445/http://www.soil-steaming-steam-boiler-blog.com/2009/10/das-regierungsprasidium-freiburg-bekampft-das-eingeschleppte-wildkraut-japan-knoterich-mit-heisem-dampf/|archive-date=16 July 2011|url-status=dead}}</ref>

Trials in [[Haida Gwaii]], [[British Columbia]], using sea water sprayed on the foliage, have not demonstrated promising results.<ref>{{cite web|author=McLean, Denise|url=https://www.for.gov.bc.ca/hra/plants/publications/Haida_Gwaii_Knotweed_Herbicide_Treatment_Demonstration.pdf|title=Haida Gwaii Knotweed Herbicide Treatment|date=July 2013|access-date=2015-06-07|archive-url=https://web.archive.org/web/20181113195353/https://www.for.gov.bc.ca/hra/plants/publications/Haida_Gwaii_Knotweed_Herbicide_Treatment_Demonstration.pdf|archive-date=2018-11-13|url-status=dead}}</ref>

===Biological===
Research has been carried out on a ''[[Mycosphaerella]]'' [[leaf spot]] fungus, which devastates knotweed in its native Japan. This research has been relatively slow due to the complex life cycle of the fungus.<ref>{{cite web|url=http://www.gardenroots.co.uk/content.php?18-Japanese-knotweed-biological-control-Aphalara-itadori |archive-url=https://archive.today/20120803033828/http://www.gardenroots.co.uk/content.php?18-Japanese-knotweed-biological-control-Aphalara-itadori |url-status=dead |archive-date=2012-08-03 |title=Notes on Biological control and Japanese knotweed |publisher=Gardenroots.co.uk |access-date=2014-06-30 }}</ref><ref>{{cite web | last=Morelle | first=Rebecca | author-link=Rebecca Morelle | url=http://news.bbc.co.uk/2/hi/science/nature/7531221.stm | title=Alien invaders hit the UK | website=BBC News | date=October 13, 2008}}</ref>

Following earlier studies, imported Japanese knotweed [[Jumping plant louse|psyllid]] insects ''[[Aphalara itadori]]'', whose only food source is Japanese knotweed, were released at a number of sites in Britain in a study running from 1 April 2010 to 31 March 2014. In 2012, results suggested that establishment and population growth were likely, after the insects overwintered successfully.<ref>{{cite web|author=Matthew Chatfield |url=http://www.naturenet.net/blogs/2010/03/tell-me-sweet-little-lice/ |title="Tell me, sweet little lice" Naturenet article on psyllid control of knotweed |publisher=Naturenet.net |date=2010-03-14 |access-date=2014-06-30}}</ref><ref name=cabi/><ref name="cabi-inv">{{cite web|url=http://www.cabi.org/japaneseknotweedalliance/ |title=Japanese Knotweed Alliance: Japanese knotweed is one of the most high profile and damaging invasive weeds in Europe and North America |publisher=Cabi.org |access-date=2014-06-30}}</ref> In 2020 [[Amsterdam]] imported and released 5,000 Japanese ''Aphalara itadori'' leaf fleas, exempting them from a strict ban on the introduction of alien species, as one of the measures to contain the knotweed. The psyllids suck up sap from the plant, potentially killing young shoots and slowing or even stopping growth. It was hoped that the psyllid would hibernate over winter and establish themselves in 2021.<ref>{{Cite web |title=Amsterdam releases 5,000 leaf fleas to halt Japanese knotweed spread |last=Boffey |first=Daniel |work=The Guardian |date=23 October 2020 |url= https://www.theguardian.com/world/2020/oct/23/amsterdam-releases-leaf-fleas-halt-japanese-knotweed-growth}}</ref>

Anecdotal reports of effective control describe the use of goats to eat the plant parts above ground followed by the use of pigs to root out and eat the underground parts of the plant.<ref>{{Cite web|url=http://www.gardensalive.com/product/got-weeds-get-goats/|title=Got Weeds? Get Goats! &#124; Gardens Alive!|access-date=2015-01-28|archive-date=2015-04-10|archive-url=https://web.archive.org/web/20150410053316/http://www.gardensalive.com/product/got-weeds-get-goats|url-status=dead}}</ref>

==Impact of the plant outside its area of origin==
[[File:Reynoutria japonica seed.jpg|thumb|Seed removed from its [[achene]]]]

===New Zealand===
Japanese knotweed is classed as an unwanted organism in [[New Zealand]] and is established in some parts of the country.<ref>{{cite web|url=http://www.biosecurity.govt.nz/pests/asiatic-knotweed|title=Asiatic knotweed|date=14 January 2010|publisher=Biosecurity New Zealand|access-date=29 December 2012|archive-url=https://web.archive.org/web/20130212024502/http://www.biosecurity.govt.nz/pests/asiatic-knotweed|archive-date=12 February 2013|url-status=dead}}</ref>

===Europe===
[[File:Japanese knotweed warning.jpg|thumb|Japanese knotweed warning in [[Lahinch]], Ireland]]

European adventurer [[Philipp Franz von Siebold]] transported Japanese knotweed from a Japanese volcano to [[Leiden]] Netherlands. By 1850, a specimen from this plant was donated by Von Siebold to the [[Royal Botanic Gardens, Kew]].<ref>{{Cite book|url=https://books.google.com/books?id=qGo3DwAAQBAJ&q=knotweed+utrecht+siebold&pg=PA142|title=The Aliens Among Us: How Invasive Species Are Transforming the Planet—and Ourselves|last=Anthony|first=Leslie|date=2017-10-24|publisher=Yale University Press|isbn=9780300231618|pages=142–143|language=en}}</ref> It was favoured by gardeners because it looked like bamboo and grew everywhere. [[Ann Conolly]] provided the first authoritative work on the history and distribution of the plant in the UK and Europe in the 1970s.<ref name="Conolly1977">{{cite journal |last1=Conolly |first1=Ann P. |title=The distribution and history in the British Isles of some alien species of Polygonum and Reynoutria |journal=Watsonia |date=1977 |volume=11 |pages=291–311 |url=http://archive.bsbi.org.uk/Wats11p291.pdf |access-date=9 May 2019}}</ref> According to ''The Daily Telegraph'', the weed has travelled rapidly, aided by rail and water networks.<ref>{{cite news| url=https://www.telegraph.co.uk/personal-banking/mortgages/japanese-knotweed-halved-value-home-network-rail-wont-pay/| title='Japanese knotweed halved the value of my home, but Network Rail won't pay'|work=The Daily Telegraph| author=Sam Meadows| date=14 August 2017| url-status=live |archive-url=https://web.archive.org/web/20121020050034/http://archive.bsbi.org.uk/Wats11p291.pdf |archive-date=2012-10-20}}</ref> In the UK, Japanese knotweed is a single female clone. However, it is able to readily hybridise with related species.<ref>{{Cite web|url=https://www2.le.ac.uk/departments/genetics/people/bailey/res/f-japonica|title=Japanese Knotweed Morphology — University of Leicester|access-date=2018-07-29|archive-date=2018-07-29|archive-url=https://web.archive.org/web/20180729171145/https://www2.le.ac.uk/departments/genetics/people/bailey/res/f-japonica|url-status=dead}}</ref>

In the UK, Japanese knotweed is established in the wild in many parts of the country and creates problems due to the impact on biodiversity, flood management and damage to property. It is an offence under section 14(2) of the [[Wildlife and Countryside Act 1981]] to "plant or otherwise cause to grow in the wild" any plant listed in Schedule nine, Part II to the Act, which includes Japanese knotweed. As of 2014, householders and landlords in residential areas who do not control the plant in their gardens, can receive an on-the-spot fine or be prosecuted.<ref name="Telegraph2014">{{cite news|last1=Riley-Smith|first1=Ben|title=Homeowners who fail to control Japanese knotweed face criminal prosecution under new anti-social behaviour laws|url=https://www.telegraph.co.uk/news/earth/greenpolitics/11185356/Homeowners-who-fail-to-control-Japanese-knotweed-face-criminal-prosecution-under-new-anti-social-behaviour-laws.html|access-date=26 July 2017|work=The Telegraph|date=25 October 2014}}</ref> It is also classed as "controlled waste" in Britain under part 2 of the [[Environmental Protection Act 1990]]. This requires disposal at licensed landfill sites.

Some home owners in the United Kingdom are unable to sell their homes if there is any evidence of knotweed on the property.{{cn|date=May 2025}} The species is expensive to remove. It cost £70 million to eradicate knotweed from 10 acres of the London 2012 Olympic Games velodrome and aquatic centre.<ref name="Macleans_2015" /><ref name="Telegraph2014" /> [[Department for Environment, Food and Rural Affairs|Defra]]'s Review of Non-native Species Policy states that a national eradication programme would be prohibitively expensive at £1.56 billion.<ref>{{cite web|title=Review of non-native species policy|publisher=Department for Environment, Food and Rural Affairs|url=http://jncc.defra.gov.uk/pdf/BRAG_NNC_DefraReviewofNon-NativeSpeciesPolicy.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://jncc.defra.gov.uk/pdf/BRAG_NNC_DefraReviewofNon-NativeSpeciesPolicy.pdf |archive-date=2022-10-09 |url-status=live|year=2003|access-date=14 July 2013}}</ref> The Centre for Ecology and Hydrology has been using [[citizen science]] to develop a system that gives a knotweed risk rating throughout Britain.<ref name="CEH-knotweed-citsci-project2017">{{cite web|last1=Pescott|first1=Oliver|title=Mapping knotweed using citizen science|url=https://www.ceh.ac.uk/news-and-media/blogs/mapping-knotweed-risk-using-citizen-science|website=Centre for Ecology and Hydrology|access-date=20 September 2017|archive-date=21 September 2017|archive-url=https://web.archive.org/web/20170921095138/https://www.ceh.ac.uk/news-and-media/blogs/mapping-knotweed-risk-using-citizen-science|url-status=dead}}</ref>

The decision was taken on 9 March 2010 in the UK to release into the wild a Japanese [[psyllid]] insect, ''[[Aphalara itadori]]''.<ref>{{cite web|last=Morelle |first=Rebecca |url=http://news.bbc.co.uk/2/hi/science/nature/8555378.stm |title=Insect that fights Japanese knotweed to be released |publisher=BBC News |date=9 March 2010 |access-date=30 June 2014}}</ref> Its diet is highly specific to Japanese knotweed and shows good potential for its control.<ref>Richard H. Shaw, Sarah Bryner and Rob Tanner. "The life history and host range of the Japanese knotweed psyllid, ''Aphalara itadori'' Shinji: Potentially the first classical biological weed control agent for the European Union".  ''UK Biological Control''. Volume 49, Issue 2, May 2009, Pages 105-113.</ref><ref>{{cite web |url=http://www.cabi.org/?page=1017&pid=1324&site=170 |title=CABI Natural control of Japanese knotweed |publisher=Cabi.org |access-date=2014-06-30 |archive-url=https://web.archive.org/web/20160304052807/http://www.cabi.org/?page=1017&pid=1324&site=170 |archive-date=2016-03-04 |url-status=dead }}</ref> Controlled release trials began in South Wales in 2016.<ref>{{cite news|work=BBC News|date=23 July 2016|url=https://www.bbc.co.uk/news/uk-wales-36868449|title=Japanese knotweed tackled with insects in secret south Wales spots|access-date=23 July 2016}}</ref>

In Scotland, the [[Wildlife and Natural Environment (Scotland) Act 2011]] came into force in July 2012, superseding the Wildlife and Countryside Act 1981. This act states that is an offence to spread, intentionally or unintentionally, Japanese knotweed (or other invasive species).

In [[Northern Ireland]], it has been recorded from Counties [[County Down|Down]], [[County Antrim|Antrim]] and [[County Londonderry|Londonderry]]. The earliest record is in 1872.<ref>Hackney, P. (Ed) 1992. ''Stewart & Corry's Flora of the North-east of Ireland Third edition.'' Institute of Irish Studies The Queen's University of Belfast {{ISBN|0-85389-446-9}}</ref>

In the [[Republic of Ireland]], it has been recorded from [[Howth Head]], County Dublin at Doldrum Bay.<ref>Dhuill, E.Ni and Smyth, N. 2021. Invasive non-native and alien garden escape plants species on the southern cliffs of Howth Head, County Dublin (H21) ''Irish Naturalists' Journal'', '''37''': 2 pp 102-108</ref>

==== United Kingdom lending controversy ====
In the United Kingdom, Japanese knotweed has received a lot of attention in the press as a result of very restrictive lending policies by banks and other mortgage companies. Several lenders have refused mortgage applications on the basis of the plant being discovered in the garden or neighbouring gardens.<ref>{{cite news |author=Leah Milner |url=https://www.thetimes.com/comment/register/article/japanese-knotweed-uproots-home-sales-zk0rs2hnsqk |title=Japanese knotweed uproots home sales |newspaper=[[The Times]] |date=2013-07-08 |access-date=2014-06-30}}</ref> The [[Royal Institution of Chartered Surveyors]] published a report in 2012 in response to lenders refusing to lend "despite [knotweed] being treatable and rarely causing severe damage to the property".<ref name="rics.org">{{cite web |url=http://www.rics.org/uk/knowledge/news-insight/press-releases/rics-targets-the-root-of-japanese-knotweed-risk-to-property/ |title=RICS targets the root of Japanese Knotweed risk to property |publisher=Rics.org |date=2013-07-05 |access-date=2014-06-30 |url-status=dead |archive-url=https://web.archive.org/web/20140307013849/http://www.rics.org/uk/knowledge/news-insight/press-releases/rics-targets-the-root-of-japanese-knotweed-risk-to-property/ |archive-date=2014-03-07 }}</ref>

{{Blockquote|There is a real lack of information and understanding of what Japanese knotweed is and the actual damage it can cause. Without actual advice and guidance, surveyors have been unsure of how to assess the risk of Japanese knotweed, which can result in inconsistent reporting of the plant in mortgage valuations. RICS hopes that this advice will provide the industry with the tools it needs to measure the risk effectively, and provide banks with the information they require to identify who and how much to lend to at a time when it is essential to keep the housing market moving.|Philip Santo, RICS Residential Professional Group<ref name="rics.org"/>}}

In response to this guidance, several lenders have relaxed their criteria in relation to discovery of the plant. As recently as 2012, the policy at the Woolwich (part of [[Barclays plc]]) was "if Japanese knotweed is found on or near the property then a case will be declined due to the invasive nature of the plant."<ref name="woolwich">{{cite web |url=https://intermediaries.uk.barclays/lending-criteria |title=Woolwich Lending Criteria }}{{Dead link|date=February 2020 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite news|url=https://www.theguardian.com/money/2012/sep/08/japanese-knotweed-house-sale |title= Japanese knotweed, the scourge that could sink your house sale |newspaper=The Guardian |date=2014-09-08}}</ref> Their criteria have since been relaxed to a category-based system depending on whether the plant is discovered on a neighbouring property (categories 1 and 2) or the property itself (categories 3 and 4) incorporating proximity to the property [[curtilage]] and the main buildings. Even in a worst-case scenario (category 4), where the plant is "within 7 metres (23 feet) of the main building, habitable spaces, conservatory and/or garage and any permanent outbuilding, either within the curtilage of the property or on neighbouring land; and/or is causing serious damage to permanent outbuildings, associated structures, drains, paths, boundary walls and fences" Woolwich lending criteria now specify that this property may be acceptable if "remedial treatment by a Property Care Association (PCA) registered firm has been satisfactorily completed. Treatment must be covered by a minimum 10-year insurance-backed guarantee, which is property specific and transferable to subsequent owners and any mortgagee in possession."<ref name="woolwich"/> Santander have relaxed their attitude in a similar fashion.
{{Citation needed|date=November 2014}} In 2022 the Royal Institution of Chartered Surveyors produced updated guidance for assessing knotweed. Since the 2012 RICS report much more information on the risks from Japanese knotweed have been gained. One important change is that the distance of a plant from a property to be considered a problem has been reduced to 3 metres (10 feet).<ref name="RICS-knotweed-guidance-2022">{{cite web |last1=Santos |first1=Philip |title=Japanese knotweed – new guidance comes into effect |url=https://ww3.rics.org/uk/en/journals/property-journal/japanese-knotweed---new-guidance-comes-into-effect.html |website=Property Journal |access-date=13 April 2022}}</ref>

Property Care Association chief executive Steve Hodgson, whose trade body has set up a task force to deal with the issue, said: "Japanese knotweed is not 'house cancer' and could be dealt with in the same way qualified contractors dealt with faulty wiring or damp."<ref>{{cite web |url=http://www.mortgagesolutions.co.uk/mortgage-solutions/news/2288807/brokers-demand-action-on-japanese-knotweed |title=Brokers demand action on Japanese knotweed |publisher=Mortgagesolutions.co.uk |date=2013-08-14 |access-date=2014-06-30 |archive-date=2014-08-10 |archive-url=https://web.archive.org/web/20140810013540/http://www.mortgagesolutions.co.uk/mortgage-solutions/news/2288807/brokers-demand-action-on-japanese-knotweed |url-status=dead }}</ref>

===United States===
[[File:Japanese-knotweed-philadelphia.jpg|thumb|Japanese knotweed along the [[Cynwyd Heritage Trail]].]]
The weed can be found in 42 of the 50 United States.<ref>{{cite web|url=https://plants.usda.gov/core/profile?symbol=POCU6|work=USDA Plants Database|title=Fallopia japonica}}</ref>

===Canada===
According to Gail Wallin, executive director of the Invasive Species Council of B.C., and co-chair of the Canadian Council on Invasive Species, by 2015 it was found in all provinces in Canada except Manitoba and Saskatchewan.<ref name="Macleans_2015">{{citation |url=http://www.macleans.ca/society/science/the-plant-thats-eating-b-c/ |title=The plant that's eating B.C.:Japanese knotweed is in nearly all our provinces. And the threat is real: it can lower house prices, threaten our bridges, and drive men to madness |author=Ken MacQueen |date=12 June 2015 |access-date=16 July 2015 |publisher=Macleans }}</ref> In Vancouver plants went under "four lanes of highway and have popped up on the other side."<ref name="Macleans_2015" /> At Mission Point Park in Davis Bay, British Columbia, municipal crews attempted to eradicate it by digging out the plant to a depth of about three metres (10 feet) with an excavator. It grew back twice as large the next year.<ref name="Macleans_2015" /> To avoid an epidemic as in the United Kingdom, some provinces in Canada are pushing for relaxation of provincial limits on the use of herbicides close to waterways so knotweed can be aggressively managed with strong chemicals. In spite of its status as an invasive species it is still sometimes sold or swapped in Canada as an edible "false bamboo".<ref name="Macleans_2015" /> [[Bohemian knotweed]], a hybrid between Japanese and giant knotweed that produces huge quantities of viable seeds, now accounts for about 80 per cent of knotweed infestations in British Columbia.<ref name="Macleans_2015" />

==Common names==
Common names for Japanese knotweed include fleeceflower, Himalayan fleece vine, billyweed, monkeyweed, monkey fungus, elephant ears, pea shooters, donkey rhubarb, American bamboo, and Mexican bamboo, among many others, depending on country and location.<ref name=cabi/> 

In [[Japanese language|Japanese]], the name is {{Nihongo|''itadori''|虎杖, イタドリ}},<ref>{{cite web |url=http://jisho.org/words?jap=itadori&eng=&dict=edict&romaji=on |title=Itadori |publisher=Denshi Jisho — Online Japanese dictionary |access-date=9 March 2010}}</ref> which uses the same ''[[kanji]]'' as the Chinese name ''huzhang'' (虎杖), meaning "tiger staff".{{efn|I.e. walking stick or cane.}}

==See also==
* [[Chinese knotweed]]
* ''[[Persicaria capitata]]'' for another plant species called Japanese knotweed

== Explanatory notes==
{{Notelist}}

==References==
{{Reflist|refs=
<ref name=POWO_435655-1>{{cite web |title=''Reynoutria japonica'' Houtt. |work=Plants of the World Online |publisher=Royal Botanic Gardens, Kew|url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:435655-1 |access-date=2019-02-25 }}</ref>
}}

==External links==
{{Commons|Reynoutria japonica}}
* [https://www.invasivespeciesinfo.gov/terrestrial/plants/japanese-knotweed Species Profile - Japanese knotweed (''Fallopia japonica'')], National Invasive Species Information Center, [[United States National Agricultural Library]], 2020
* [http://extension.umn.edu/identify-invasive-species/japanese-knotweed Japanese knotweed], [[University of Minnesota Extension]], 2023
* [https://www.bbc.com/future/article/20221006-the-race-to-kill-the-worlds-most-invasive-weed The alien shrub that can't be stopped] – BBC Future, 2022

{{Taxonbar|from1=Q18421053|from2=Q899672|from3=Q15250539}}
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[[Category:Flora of China]]
[[Category:Flora of Eastern Asia]]
[[Category:Garden plants of Asia]]
[[Category:Medicinal plants]]
[[Category:Plants described in 1777]]
[[Category:Polygonoideae]]
[[Category:Stem vegetables]]