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''Reynoutria japonica'', synonyms ''Fallopia japonica'' and ''Polygonum cuspidatum'', is a
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
of
herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition o ...
perennial plant A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...
in the knotweed and buckwheat family
Polygonaceae The Polygonaceae are a family of flowering plants known informally as the knotweed family or smartweed—buckwheat family in the United States. The name is based on the genus ''Polygonum'', and was first used by Antoine Laurent de Jussieu in ...
. Common names include Japanese knotweed and Asian knotweed. It is native to
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea ...
in
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
and
Korea Korea ( ko, 한국, or , ) is a peninsular region in East Asia. Since 1945, it has been divided at or near the 38th parallel, with North Korea (Democratic People's Republic of Korea) comprising its northern half and South Korea (Republic ...
. In
North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...
and
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
, the species has successfully established itself in numerous habitats, and is classified as a pest and
invasive species An invasive species otherwise known as an alien is an introduced organism that becomes overpopulated and harms its new environment. Although most introduced species are neutral or beneficial with respect to other species, invasive species adv ...
in several countries. Japanese knotweed has hollow stems with distinct raised
node In general, a node is a localized swelling (a " knot") or a point of intersection (a vertex). Node may refer to: In mathematics * Vertex (graph theory), a vertex in a mathematical graph * Vertex (geometry), a point where two or more curves, line ...
s that give it the appearance of
bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...
, though it is not related. While stems may reach a maximum height of 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 A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, st ...
are broad oval with a truncated base, long and broad, with an entire margin. The
flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanis ...
s are small, cream or white, produced in erect
raceme A raceme ( or ) or racemoid is an unbranched, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are produced as the s ...
s long in late summer and early autumn. Related species include giant knotweed (''
Reynoutria sachalinensis ''Reynoutria sachalinensis'' (giant knotweed or Sakhalin knotweed Japanese オオイタドリ ''ooitadori'', Russian Горец сахалинский, Гречиха сахалинская; syns. ''Polygonum sachalinense'', ''Fallopia sachaline ...
'', syns. ''Fallopia sachalinensis'', ''Polygonum sachalinense'') and Russian vine (''
Fallopia baldschuanica ''Fallopia baldschuanica'' ( syn. ''Polygonum baldschuanicum'') is an Asian species of flowering plant in the knotweed family known by several common names, including Russian-vine, Bukhara fleeceflower, Chinese fleecevine, mile-a-minute and sil ...
'', syn. ''Polygonum baldschuanicum'').


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. In Japanese, the name is . The kanji expression is from the Chinese meaning 'tiger stick'. One interpretation of the Japanese name is that it comes from 'remove pain' (alluding to its painkilling use), though there are other etymological explanations offered.


Identification

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 ''Cornus'' is a genus of about 30–60 species of woody plants in the family Cornaceae, commonly known as dogwoods, which can generally be distinguished by their blossoms, berries, and distinctive bark. Most are deciduous trees or ...
,
lilac ''Syringa'' is a genus of 12 currently recognized species of flowering woody plants in the olive family or Oleaceae called lilacs. These lilacs are native to woodland and scrub from southeastern Europe to eastern Asia, and widely and commonl ...
,
houttuynia ''Houttuynia'' is a genus of two species in the Saururaceae native to Southeast Asia. One species, '' H. cordata'', is widely cultivated as a culinary herb. The genus was originally described in 1783 by Carl Peter Thunberg when he formally ...
(''Houttuynia cordata''), ornamental
bistort Bistort is a common name for several plants and may refer to: *'' Bistorta'', a genus recognized by some sources including the species: **'' Bistorta bistortoides'', native to North America **'' Bistorta officinalis'' (''Persicaria bistorta''), ...
s such as red bistort (''
Persicaria amplexicaulis ''Bistorta amplexicaulis'' (synonym ''Persicaria amplexicaulis''), the red bistort or mountain fleece, is a species of flowering plant in the buckwheat family Polygonaceae, native to China, the Himalayas, and Pakistan. It is a damp-loving herbace ...
)'', lesser knotweed (''
Koenigia campanulata ''Koenigia campanulata'' is a species of flowering plant in the family Polygonaceae. It is native to China (Guizhou, west Hubei, Sichuan, Yunnan and Tibet), Bhutan, north Myanmar, Nepal and Sikkim Sikkim (; ) is a state in Northeastern India ...
''), Himalayan balsam ('' Impatiens glandulifera''), broad-leaved dock (''
Rumex obtusifolius ''Rumex obtusifolius'', commonly known as bitter dock, broad-leaved dock, bluntleaf dock, dock leaf, dockens or butter dock, is a perennial plant in the family Polygonaceae. It is native to Europe, but is found on all temperate continents. It i ...
''), bindweed ('' Convolvulus arvensis''),
bamboo Bamboos are a diverse group of evergreen perennial flowering plants making up the subfamily Bambusoideae of the grass family Poaceae. Giant bamboos are the largest members of the grass family. The origin of the word "bamboo" is uncertain, ...
, Himalayan honeysuckle ('' Leycesteria formosa''), and Russian vine (''
Fallopia baldschuanica ''Fallopia baldschuanica'' ( syn. ''Polygonum baldschuanicum'') is an Asian species of flowering plant in the knotweed family known by several common names, including Russian-vine, Bukhara fleeceflower, Chinese fleecevine, mile-a-minute and sil ...
'') have been suspected of being ''Reynoutria japonica''. New leaves of ''Reynoutria japonica'' are dark red and 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 long. Mature ''R.japonica'' forms , dense thickets. The stems look somewhat like bamboo, with rings and purple speckles. Leaves shoot from the stem nodes alternately in a zigzag pattern. Mature, healthy stems are hollow and not woody. Plants that are immature or affected by mowing and other restrictions have much thinner and shorter stems than mature stands, and are not hollow.


Uses

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 A beekeeper is a person who keeps honey bees. Beekeepers are also called honey farmers, apiarists, or less commonly, apiculturists (both from the Latin '' apis'', bee; cf. apiary). The term beekeeper refers to a person who keeps honey bees i ...
s, like a mild-flavoured version of
buckwheat Buckwheat (''Fagopyrum esculentum''), or common buckwheat, is a flowering plant in the knotweed family Polygonaceae cultivated for its grain-like seeds and as a cover crop. The name "buckwheat" is used for several other species, such as ''Fagop ...
honey (a related plant also in the Polygonaceae). The young stems are edible as a spring
vegetable Vegetables are parts of plants that are consumed by humans or other animals as food. The original meaning is still commonly used and is applied to plants collectively to refer to all edible plant matter, including the edible flower, flowers, ...
, with a flavour similar to
rhubarb Rhubarb is the fleshy, edible stalks ( petioles) of species and hybrids (culinary rhubarb) of '' Rheum'' in the family Polygonaceae, which are cooked and used for food. The whole plant – a herbaceous perennial growing from short, thick rhi ...
. 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. It is eaten in Japan as ''
sansai is a Japanese word literally meaning "mountain vegetables", originally referring to vegetables that grew naturally, were foraged in the wild, and not grown and harvested from fields. However, in modern times, the distinction is somewhat blur ...
'' or wild foraged vegetable. It is used in
traditional Chinese A tradition is a belief or behavior (folk custom) passed down within a group or society with symbolic meaning or special significance with origins in the past. A component of cultural expressions and folklore, common examples include holidays ...
and Japanese medicine to treat various disorders through the actions of
resveratrol Resveratrol (3,5,4′-trihydroxy-''trans''-stilbene) is a stilbenoid, a type of natural phenol, and a phytoalexin produced by several plants in response to injury or when the plant is under attack by pathogens, such as bacteria or fungi. Sourc ...
, although there is no high-quality evidence from
clinical research Clinical research is a branch of healthcare science that determines the safety and effectiveness ( efficacy) of medications, devices, diagnostic products and treatment regimens intended for human use. These may be used for prevention, treat ...
for any medical efficacy.
Extract An extract is a substance made by extracting a part of a raw material, often by using a solvent such as ethanol, oil or water. Extracts may be sold as tinctures, absolutes or in powder form. The aromatic principles of many spices, nuts ...
s of resveratrol from ''R. japonica'' roots are higher in content than those from stems or leaves, and have highest levels at the end of the growing season. Ground-feeding songbirds and gamebirds also eat the seeds.


In Japan

It grows widely throughout Japan and is foraged as a wild edible vegetable (''
sansai is a Japanese word literally meaning "mountain vegetables", originally referring to vegetables that grew naturally, were foraged in the wild, and not grown and harvested from fields. However, in modern times, the distinction is somewhat blur ...
''), though not in sufficient quantities to be included in statistics. They are called by such regional names as ''tonkiba'' ( Yamagata), ''itazuiko'' ( Nagano, Mie), ''itazura'' (
Gifu is a city located in the south-central portion of Gifu Prefecture, Japan, and serves as the prefectural capital. The city has played an important role in Japan's history because of its location in the middle of the country. During the Sengoku p ...
, Toyama,
Nara The National Archives and Records Administration (NARA) is an " independent federal agency of the United States government within the executive branch", charged with the preservation and documentation of government and historical records. It ...
, Wakayama, Kagawa), ''gonpachi'' ( Shizuoka, Nara, Mie, Wakayama), ''sashi'' (
Akita is a Japanese name and may refer to: Places * 8182 Akita, a main-belt asteroid * Akita Castle, a Nara period fortified settlement in Akita, Japan * Akita Domain, also known as Kubota Domain, feudal domain in Edo period Japan * Akita, Kumamoto ...
, Yamagata), ''jajappo'' ( Shimane, Tottori, Okayama), ''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 is the smallest of the four main islands of Japan. It is long and between wide. It has a population of 3.8 million (, 3.1%). It is south of Honshu and northeast of Kyushu. Shikoku's ancient names include ''Iyo-no-futana-shima'' (), '' ...
such as central parts of
Kagawa Prefecture is a prefecture of Japan located on the island of Shikoku. Kagawa Prefecture has a population of 949,358 (as of 2020) and is the smallest prefecture by geographic area at . Kagawa Prefecture borders Ehime Prefecture to the southwest and Tok ...
pickle the peeled young shoots by weighting them down in salt mixed with 10%
nigari Bittern (pl. bitterns), or nigari, is the salt solution formed when halite (table salt) precipitates from seawater or brines. Bitterns contain magnesium, calcium, and potassium ions as well as chloride, sulfate, iodide, and other ions. Bittern i ...
(magnesium chloride). People in
Kochi Kochi (), also known as Cochin ( ) ( the official name until 1996) is a major port city on the Malabar Coast of India bordering the Laccadive Sea, which is a part of the Arabian Sea. It is part of the district of Ernakulam in the state of ...
also rub these cleaned shoots with coarse salt-nigari blend. It is said (though no authority is cited) that the
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ...
of the ''nigari'' binds with the oxalic acid thus mitigating its hazard.


Invasive species

This species is listed by the
World Conservation Union The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natur ...
as one of the world's worst invasive species. It is a frequent colonizer of
temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...
riparian A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks a ...
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
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, different soil types, variable soil pH, and high salinity. Its
rhizomes In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow ...
can survive temperatures of and can extend horizontally and deep, making removal by excavation extremely difficult. The plant is also resilient to cutting, vigorously resprouting from the roots.


Impact

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 water. Japanese knotweed shades out other
vegetation Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic charac ...
, overgrows buildings and other structures, encourages fire, and damages paved surfaces.


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

The abundance of the plant can be significantly reduced by applying glyphosate,
imazapyr Imazapyr is a non-selective herbicide used for the control of a broad range of weeds including terrestrial annual and perennial grasses and broadleaved herbs, woody species, and riparian and emergent aquatic species. It is used to eliminate ''L ...
, 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 population.


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 deep, and leaving only 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. Trials in
Haida Gwaii Haida Gwaii (; hai, X̱aaydag̱a Gwaay.yaay / , literally "Islands of the Haida people") is an archipelago located between off the northern Pacific coast of Canada. The islands are separated from the mainland to the east by the shallow Heca ...
,
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
, using sea water sprayed on the foliage, have not demonstrated promising results.


Biological

Research has been carried out on a '' Mycosphaerella''
leaf spot A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions ...
fungus, which devastates knotweed in its native Japan. This research has been relatively slow due to the complex life cycle of the fungus. 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 successfully. In 2020
Amsterdam Amsterdam ( , , , lit. ''The Dam on the River Amstel'') is the capital and most populous city of the Netherlands, with The Hague being the seat of government. It has a population of 907,976 within the city proper, 1,558,755 in the urban ar ...
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. 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.


Impact of the plant outside its area of origin


New Zealand

Japanese knotweed is classed as an unwanted organism in
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
and is established in some parts of the country.


Europe

European adventurer
Philipp Franz von Siebold Philipp Franz Balthasar von Siebold (17 February 1796 – 18 October 1866) was a German physician, botanist and traveler. He achieved prominence by his studies of Japanese flora and fauna and the introduction of Western medicine in Japan. He w ...
transported Japanese knotweed from a Japanese volcano to Leiden in the Netherlands. By 1850, a specimen from this plant was donated by Von Siebold to the
Royal Botanic Gardens, Kew Royal Botanic Gardens, Kew is a non-departmental public body in the United Kingdom sponsored by the Department for Environment, Food and Rural Affairs. An internationally important botanical research and education institution, it employs 1,100 ...
. 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 networks. In the UK, Japanese knotweed is a single female clone. However, it is able to readily hybridise with related species. 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 14(2) of the
Wildlife and Countryside Act 1981 The Wildlife and Countryside Act 1981 is an Act of Parliament in the United Kingdom implemented to comply with European Council Directive 79/409/EEC on the conservation of wild birds. In short, the act gives protection to native species (especia ...
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 within towns, who do not control the plant in their gardens, can receive an on-the-spot fine or be prosecuted. 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. The species is expensive to remove. According to the UK government, the cost of controlling knotweed had hit £1.25 billion in 2014. It cost £70 million to eradicate knotweed from 10 acres of the London 2012 Olympic Games velodrome and aquatic centre. Defra's Review of Non-native Species Policy states that a national eradication programme would be prohibitively expensive at £1.56 billion. The Centre for Ecology and Hydrology has been using
citizen science Citizen science (CS) (similar to community science, crowd science, crowd-sourced science, civic science, participatory monitoring, or volunteer monitoring) is scientific research conducted with participation from the public (who are sometimes r ...
to develop a system that gives a knotweed risk rating throughout Britain. The decision was taken on 9 March 2010 in the UK to release into the wild a Japanese psyllid insect, '' Aphalara itadori''. Its diet is highly specific to Japanese knotweed and shows good potential for its control. Controlled release trials began in South Wales in 2016. 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). In
Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label=Ulster Scots dialect, Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is #Descriptions, variously described as ...
it has been recorded from Counties Down, Antrim and Londonderry. The earliest record is in 1872. In the Republic of Ireland, it has been recorded from Howth Head, Co. Dublin at Doldrum Bay.


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. The
Royal Institution of Chartered Surveyors The Royal Institution of Chartered Surveyors (RICS) is a global professional body for surveyors, founded in London in 1868. It works at a cross-governmental level, and aims to promote and enforce the highest international standards in the va ...
published a report in 2012 in response to lenders refusing to lend "despite notweedbeing treatable and rarely causing severe damage to the property". 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." 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." Santander have relaxed their attitude in a similar fashion. 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). 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."


United States

The weed can be found in 42 of the 50 United States.


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. In Vancouver the aggressive plant went under "four lanes of highway and have popped up on the other side." 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. 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." 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.


See also

* ''
Persicaria capitata ''Persicaria capitata'', the pink-headed persicaria, pinkhead smartweed, pink knotweed, Japanese knotweed, or pink bubble persicaria, is an Asian species of plants in the genus ''Persicaria'' within the buckwheat family. It is native to Asia (Ch ...
'' for another plant species called Japanese knotweed. * Chinese knotweed


References


External links


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 The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Located ...
. Lists general information and resources for Japanese knotweed.
Best management practice
A variety of ways to control knotweed (under "knotweed")(USA)


American Journal of Botany - Sexual Reproduction in the Invasive Species ''Fallopia japonica''

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 BBC News is an operational business division of the British Broadcasting Corporation (BBC) responsible for the gathering and broadcasting of news and current affairs in the UK and around the world. The department is the world's largest broadc ...
2010-03-09
How close is Japanese Knotweed to my home?
BBC News BBC News is an operational business division of the British Broadcasting Corporation (BBC) responsible for the gathering and broadcasting of news and current affairs in the UK and around the world. The department is the world's largest broadc ...
11 August 2017
UK location map
at planttracker.org.uk *
The alien shrub that can't be stopped
– BBC Future {{Authority control Flora of Eastern Asia Garden plants of Asia Medicinal plants Polygonoideae Stem vegetables Plants described in 1777 Flora of China