Mon . 19 Apr 2019

Fallopia japonica

fallopia japonica, fallopia japonica variegata
Fallopia japonica, synonym Reynoutria japonica, commonly known as Asian knotweed2 or Japanese knotweed,3 is a large, herbaceous perennial plant of the knotweed and buckwheat family Polygonaceae It is native to East Asia in Japan, China and Korea In North America and Europe, the species has successfully established in numerous habitats and is classified as an invasive species in several countries45

Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo, though it is not related While stems may reach a maximum height of 3–4 m 98–131 ft 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 leaves are broad oval with a truncated base, 7–14 cm 28–55 in long and 5–12 cm 20–47 in broad,6 with an entire margin The flowers are small, cream or white, produced in erect racemes 6–15 cm 24–59 in long in late summer and early autumn

Closely related species include giant knotweed Fallopia sachalinensis, syn Polygonum sachalinense and Russian vine Fallopia baldschuanica, Polygonum baldschuanicum

Other English names for Japanese knotweed include fleeceflower, Himalayan fleece vine, monkeyweed, monkey fungus, Hancock's curse, elephant ears, pea shooters, donkey rhubarb although it is not a rhubarb, sally rhubarb, Japanese bamboo, American bamboo, and Mexican bamboo though it is not a bamboo In Chinese medicine, it is known as Huzhang Chinese: 虎杖; pinyin: Hǔzhàng, which translates to "tiger stick" There are also regional names, and it is sometimes confused with sorrel In Japanese, the name is itadori 虎杖, イタドリ7

Old stems remain in place as new growth appears A hedgerow made up of roses and Japanese knotweed in Caersws, Wales, in 2010 Erect inflorescence


  • 1 Uses
  • 2 Japan
  • 3 Invasive species
    • 31 Identification
    • 32 Control
    • 33 New Zealand
    • 34 United Kingdom
      • 341 Lending controversy
    • 35 United States
    • 36 Canada
  • 4 See also
  • 5 References
  • 6 External links


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 US beekeepers, like a mild-flavoured version of buckwheat honey a related plant also in the Polygonaceae

The young stems are edible as a spring vegetable, with a flavour similar to extremely sour rhubarb 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 vegetation8 It is eaten in Japan as sansai or wild foraged vegetable

It is used in traditional Chinese medicine and traditional Japanese medicine to treat fungal infections, various skin inflammations, and cardiovascular diseases; one active ingredient is thought to be resveratrol and its glucoside piceid9

This antique locomotive at Beekbergen, Netherlands, is overgrown by knotweed A few years before, it was free of knotweed


The plant is known as itadori 虎杖 The kanji expression is from the Chinese meaning "tiger staff" One interpretation of the Japanese name is that it comes from "remove pain" alluding to its painkilling use,1011 though there are other etymological explanations offered

It grows widely throughout Japan and is foraged as a wild edible vegetable sansai, though not in sufficient quantities to be included in statistics12 They are called by such regional names as tonkiba Yamagata,12 itazuiko Nagano, Mie,12 itazura Gifu, Toyama, Nara, Wakayama, Kagawa,12 gonpachi Shizuoka, Nara, Mie, Wakayama,12 sashi Akita, Yamagata,12 jajappo Shimane, Tottori, Okayama,12 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

Places in Shikoku such as central parts of Kagawa Prefecture13 pickle the peeled young shoots by weighting them down in salt mixed with 10% nigari magnesium chloride People in Kochi also rub these cleaned shoots with coarse salt-nigari blend It is said though no authority is cited that the magnesium of the nigari binds with the oxalic acid thus mitigating its hazard14

Invasive speciesedit

It is listed by the World Conservation Union as one of the world's worst invasive species15

The invasive root system and strong growth can damage concrete foundations, buildings, flood defences, roads, paving, retaining walls and architectural sites It can also reduce the capacity of channels in flood defences to carry water16

It is a frequent colonizer of temperate riparian ecosystems, 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 soil types, pH and salinity Its rhizomes can survive temperatures of −35 °C −31 °F and can extend 7 metres 23 ft horizontally and 3 metres 98 ft deep, making removal by excavation extremely difficult The plant is also resilient to cutting, vigorously resprouting from the roots


Identification of Japanese knotweed is not always easy Many other plants are suspected of being knotweed, due often to the similar appearance of leaves and stems Dogwood, lilac, Houttuynia Houttuynia cordata, ornamental Bistorts such as Red Bistort Persicaria amplexicaulis, lesser knotweed Persicaria campanulata, Himalayan Balsam Impatiens glandulifera, Broadleaved Dock Rumex obtusifolius, Bindweed Convolvulus arvensis, bamboo, Himalayan Honeysuckle Leycesteria formosa, and Russian Vine Fallopia baldschuanica have been suspected of being Fallopia japonica17

New leaves of Fallopia japonica are dark red and 1 to 4 cm 04 to 16 in 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 12 cm 47 in long Mature F japonica forms 2-to-3-metre 66 to 98 ft tall dense thickets; stems look somewhat like bamboo, with rings and purple speckles Leaves shoot from the stem nodes alternately in a zigzag pattern Mature stems are hollow and not at all woody: they can be snapped easily to see if they are hollow Plants that are immature or affected by mowing or other restrictions have much thinner and shorter stems than mature stands, and are not hollow18


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

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 completely eliminating the treated population19

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 efficient The roots can go to up to 10 feet 30 meters deep, and leaving only a few 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

More ecologically-friendly means are being tested as an alternative to chemical treatments Soil steam sterilization20 involves injecting steam into contaminated soil in order to kill subterranean plant parts Research has also been carried out on Mycosphaerella leafspot fungus, which devastates knotweed in its native Japan This research has been relatively slow due to the complex life cycle of the fungus21

Two biological pest control agents that show promise in the control of the plant are a leaf spot fungus from genus Mycosphaerella 22 and the psyllid Aphalara itadori23 Research has been carried out by not-for-profit inter-governmental organisation CABI in the UK Following earlier studies imported Japanese knotweed 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 successfully2425

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 plant26

Detail of the stalk

The most effective method of control is by herbicide application close to the flowering stage in late summer or autumn In some cases, it is possible to eradicate Japanese knotweed in one growing season using only herbicides Glyphosate is widely used as it is non-persistent and, certain formulations, may be used in or near water27

Trials in Haida Gwaii, British Columbia, using sea water sprayed on the foliage, have not demonstrated promising results28

New Zealandedit

Japanese knotweed is classed as an unwanted organism in New Zealand and is established in some parts of the country29

United Kingdomedit

European adventurer Philipp Franz von Siebold transported Japanese knotweed from a Japanese volcano to Holland By 1850 a specimen from this plant was added to the Royal Botanic Gardens, Kew 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 According to the Daily Telegraph, the weed has travelled rapidly, aided by rail and water networks30 Some home owners in the United Kingdom are unable to sell their homes if there is any evidence of knotweed on the property

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, flooding management and damage to property It is an offence under section 142 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 Within towns householders and landlords in 2014 who did not control the plant in their gardens could receive an on-the-spot fine or be prosecuted31 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

The species is expensive to remove According to the UK government, the cost of controlling knotweed had hit £125 billion in 201431 It cost £70 million to eradicate knotweed from 10 acres of the London 2012 Olympic Games velodrome and aquatic centre3231 Defra's Review of Non-native Species Policy states that a national eradication programme would be prohibitively expensive at £156 billion33 The Centre for Ecology and Hydrology has been using citizen science to develop a system that gives a knotweed risk rating throughout Britain34

The decision was taken on 9 March 2010 in the UK to release into the wild a Japanese psyllid insect, Aphalara itadori35 Its diet is highly specific to Japanese knotweed and shows good potential for its control3637 Controlled release trials began in South Wales in 201638

In Scotland, the Wildlife and Natural Environment Scotland Act 2011 came into force in July 2012 that superseded the Wildlife and Countryside Act 1981 This act states that is an offence to spread intentionally or unintentionally Japanese knotweed or other non-native invasive species

Lending controversyedit

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 garden39 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"40

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 Group40

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"4142 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 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"41 Santander have relaxed their attitude in a similar fashioncitation needed

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"43

United Statesedit

The weed can be found in 39 of the 50 United States44 It is listed as an invasive weed in Maine, New Hampshire, Ohio, Vermont, Virginia, West Virginia, New York, New Jersey, Alaska, Pennsylvania, Michigan, Oregon, Washington state, Wisconsin, Minnesota and Colorado45


According to Gail Wallin, executive director of the Invasive Species Council of BC, and co-chair of the Canadian Council on Invasive Species, by 2015 it was found in all provinces in Canada except Manitoba and Saskatchewan32 In Vancouver the aggressive plant went under "four lanes of highway and have popped up on the other side"32 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 with an excavator It grew back twice as large the next year32 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"32 Bohemian knotweed, a mutant hybrid— which is a cross between Japanese and giant knotweed that produces huge quantities of viable seeds —now accounts for about 80 per cent of knotweed infestations in British Columbia32

See alsoedit

  • Persicaria capitata for another plant species called Japanese knotweed


  1. ^ "The Plant List, Reynoutria japonica Houtt" Royal Botanic Gardens Kew and Missouri Botanic Garden Retrieved 20 February 2017 
  2. ^ English Names for Korean Native Plants PDF Pocheon: Korea National Arboretum 2015 p 358 ISBN 978-89-97450-98-5 Archived from the original PDF on 25 May 2017 Retrieved 4 January 2017 – via Korea Forest Service 
  3. ^ "BSBI List 2007" Botanical Society of Britain and Ireland Archived from the original xls on 2015-01-25 Retrieved 2014-10-17 
  4. ^ "How to deal with Japanese knotweed and other invasive plants" Sunday Express 2014 
  5. ^ "Japanese Knotweed, Reynoutria japonica var japonica" Invading Species Awareness Program, Ontario Ministry of Natural Resources and Forestry, Peterborough, Ontario Canada 2012 Retrieved 2 August 2017 
  6. ^ "Japanese knotweed" Royal Horticultural Society Retrieved 6 June 2014 
  7. ^ "itadori" Denshi Jisho — Online Japanese dictionary Retrieved 9 March 2010 
  8. ^ "Pilot project of Bionic Knotweed Control in Wiesbaden, Germany" Newtritioninkde Retrieved 2014-06-30 
  9. ^ Wenzel E, Somoza V; Somoza May 2005 "Metabolism and bioavailability of trans-resveratrol" Mol Nutr Food Res 49 5: 472–81 doi:101002/mnfr200500010 PMID 15779070 
  10. ^ 日本國語大辞典 Nihon kokugo daijiten dictionary 1976
  11. ^ Daigenkai 大言海 dictionary, citing Wakunsai『和訓菜』
  12. ^ a b c d e f g "山菜関係資料 - 山菜文化産業懇話会報告書" Wild vegetable related document - Wakami culture industry conference report Forestry Agency 2004 
  13. ^ "イタドリ" Local cuisine and traditional ingredients > Itadori 讃岐の食Sanuki eating 2001 
  14. ^ Given in Japanese wiki article ja:イタドリ, traced to contribution 2006217 Fri 16:23 by ウミユスリカ
  15. ^ Lowe S, Browne M, Boudjelas S, De Poorter M 1 December 2000 "100 of the World's Worst Invasive Alien Species: A Selection from the Global Invasive Species Database" PDF The Invasive Species Specialist Group, a Specialist Group of the Species Survival Commission of the World Conservation Union p 6 Retrieved 4 January 2017 CS1 maint: Uses authors parameter link
  16. ^ "Article on the costs of Japanese Knotweed" Gardenrootscouk Archived from the original on 2012-09-04 Retrieved 2014-06-30 
  17. ^ "Plants That Look Similar To Japanese Knotweed: Plants Mistaken For Knotweed" Phlorumcom Retrieved 26 June 2017 
  18. ^ "How To Identify Japanese Knotweed, Knotweed Identification Card & Pictures" Phlorumcom Retrieved 26 June 2017 
  19. ^ "Fallopia japonica Japanese knotweed" Invasive Species Compendium 4 January 2017 
  21. ^ "Notes on Biological control and Japanese knotweed" Gardenrootscouk Archived from the original on 2012-08-03 Retrieved 2014-06-30 
  22. ^ Morelle, R Alien invaders hit the UK BBC News October 13, 2008
  23. ^ Matthew Chatfield 2010-03-14 ""Tell me, sweet little lice" Naturenet article on psyllid control of knotweed" Naturenetnet Retrieved 2014-06-30 
  24. ^ "Testing the psyllid: first field studies for biological control of knotweed United Kingdom" CABI Retrieved 2014-06-30 
  25. ^ "On CABI Web site, Japanese Knotweed Alliance: Japanese knotweed is one of the most high profile and damaging invasive weeds in Europe and North America" Cabiorg Retrieved 2014-06-30 
  26. ^ http://wwwgardensalivecom/product/got-weeds-get-goats/
  27. ^ "The Knotweed Code of Practice" PDF govuk Environment Agency 
  28. ^ McLean, Denise July 2013 "Haida Gwaii Knotweed Herbicide Treatment" PDF 
  29. ^ "Asiatic knotweed" Biosecurity New Zealand 14 January 2010 Retrieved 29 December 2012 
  30. ^ Sam Meadows 14 August 2017 "'Japanese knotweed halved the value of my home, but Network Rail won't pay'" Daily Telegraph Retrieved 20 August 2017 
  31. ^ a b c Riley-Smith, Ben 25 October 2014 "Homeowners who fail to control Japanese knotweed face criminal prosecution under new anti-social behaviour laws" The Telegraph Retrieved 26 July 2017 
  32. ^ a b c d e f Ken MacQueen 12 June 2015, The plant that’s eating BC: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, Macleans, retrieved 16 July 2015 
  33. ^ "Review of non-native species policy" PDF Department for Environment, Food and Rural Affairs 2003 Retrieved 14 July 2013 
  34. ^ Pescott, Oliver "Mapping knotweed using citizen science" Centre for Ecology and Hydrology Retrieved 20 September 2017 
  35. ^ Morelle, Rebecca 9 March 2010 "Insect that fights Japanese knotweed to be released" BBC News Retrieved 30 June 2014 
  36. ^ 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
  37. ^ "CABI Natural control of Japanese knotweed" Cabiorg Retrieved 2014-06-30 
  38. ^ "Japanese knotweed tackled with insects in secret south Wales spots" BBC News 23 July 2016 Retrieved 23 July 2016 
  39. ^ Leah Milner 2013-07-08 "Japanese knotweed uproots home sales" The Times Retrieved 2014-06-30 
  40. ^ a b 5 July 2013 2013-07-05 "RICS targets the root of Japanese Knotweed risk to property" Ricsorg Archived from the original on 2014-03-07 Retrieved 2014-06-30 
  41. ^ a b "Woolwich Lending Criteria" 
  42. ^ "Japanese knotweed, the scourge that could sink your house sale" The Guardian 2014-09-08 
  43. ^ "Brokers demand action on Japanese knotweed" Mortgagesolutionscouk 2013-08-14 Retrieved 2014-06-30 
  44. ^ "Fallopia japonica" USDA Plants Database 
  45. ^ "USDA weed profile for Japanese knotweed" National Invasive Species Information Center Retrieved 2014-06-30 

External linksedit

  • Photo of herbarium specimen at Missouri Botanical Garden, collected in Missouri in 1994
  • Species Profile- Japanese knotweed Fallopia japonica, National Invasive Species Information Center, United States National Agricultural Library Lists general information and resources for Japanese knotweed
  • Best management practice A variety of ways to control knotweed under "knotweed"USA
  • Strategies for the eradication of Japanese knotweed
  • American Journal of Botany - Sexual Reproduction in the Invasive Species Fallopia japonica
  • Knotweed page on KnottyBitscom
  • Japanese Knotweed Alliance UK
  • Recipes from "Wildman" Steve Brill
  • Time lapse video of knotweed growth BBC
  • Insect that fights Japanese knotweed to be released BBC News 2010-03-09

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