Japanese Knotweed is a large,
herbaceousA herbaceous plant is a plant that has leaves and stems that die down at the end of the growing season to the soil level. They have no persistent woody stem above ground...
perennial plantA perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...
, native to eastern Asia in Japan, China and Korea. In North America and Europe the species is very successful and has been classified as an
invasive species"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
in several countries.
A member of the family
PolygonaceaePolygonaceae is a family of flowering plants known informally as the "knotweed family" or "smartweed family"— "buckwheat family" in the United States. The name is based on the genus Polygonum and was first used by Antoine Laurent de Jussieu in 1789 in his book, Genera Plantarum. The name refers...
, Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of
bambooBamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
, though it is not closely related. While stems may reach a maximum height of 3–4 m 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
leavesA leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
are broad oval with a truncated base, 7–14 cm long and 5–12 cm broad, with an entire margin. The
flowerA flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s are small, cream or white, produced in erect
racemeA raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...
s 6–15 cm long in late summer and early autumn.
Closely related species include giant knotweed (
Fallopia sachalinensisFallopia sachalinensis Fallopia sachalinensis Fallopia sachalinensis (Giant Knotweed or Sakhalin Knotweed Japanese オオイタドリ ooitadori, Russian Горец сахалинский, Гречиха сахалинская; syn...
, syn.
Polygonum sachalinense) and Russian vine (
Fallopia baldschuanicaFallopia baldschuanica is a species of flowering plant in the knotweed family known by several common names, including Russian vine, Bukhara fleeceflower, Chinese fleecevine, mile-a-minute and silver lace vine...
, syn.
Polygonum aubertii,
Polygonum baldschuanicum).
Other English names for Japanese knotweed include fleeceflower, Himalayan fleece vine, monkeyweed, Huzhang , Hancock's curse, elephant ears, pea shooters, donkey rhubarb (although it is not a
rhubarbRhubarb is a group of plants that belong to the genus Rheum in the family Polygonaceae. They are herbaceous perennial plants growing from short, thick rhizomes. They have large leaves that are somewhat triangular-shaped with long fleshy petioles...
), sally rhubarb, Japanese bamboo, American bamboo, and Mexican bamboo (though it is not a
bambooBamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
). There are also regional names, and it is sometimes confused with
sorrelCommon sorrel or garden sorrel , often simply called sorrel, is a perennial herb that is cultivated as a garden herb or leaf vegetable...
.
In Japanese, the name is .
Invasive species
In the U.S. and Europe, Japanese knotweed is widely considered an
invasive species"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
or
weedA weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...
. It is listed by the
World Conservation UnionThe International Union for Conservation of Nature and Natural Resources is an international organization dedicated to finding "pragmatic solutions to our most pressing environment and development challenges." The organization publishes the IUCN Red List, compiling information from a network of...
as one of the
world's 100 worst invasive species.
The invasive root system and strong growth can damage foundations, buildings, flood defences, roads, paving, retaining walls and architectural sites. It can also reduce the capacity of channels in flood defenses to carry water.
It is a frequent colonizer of
temperateIn geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
riparian
ecosystemAn ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
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 soil types, pH and salinity. Its rhizomes can survive temperatures of -35 °C and can extend 7 metres (23 ft) horizontally and 3 metres (9.8 ft) deep, making removal by excavation extremely difficult. The plant is also resilient to cutting, vigorously re-sprouting from the roots. The most effective method of control is by
herbicideHerbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
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. Trials in the
Queen Charlotte IslandsHaida Gwaii , formerly the Queen Charlotte Islands, is an archipelago on the North Coast of British Columbia, Canada. Haida Gwaii consists of two main islands: Graham Island in the north, and Moresby Island in the south, along with approximately 150 smaller islands with a total landmass of...
(Haida Gwaii) of British Columbia using sea water sprayed on the foliage have demonstrated promising results, which may prove to be a viable option for eradication where concerns over herbicide application are too great.
It can be found in 39 of the 50 United States and in six provinces in Canada. It is listed as an invasive weed in Ohio, Vermont, Virginia, West Virginia, New York, Alaska, Pennsylvania, Oregon and Washington state. The species is also common in Europe. In the UK it was made illegal to spread Japanese knotweed by the
Wildlife and Countryside Act 1981The Wildlife and Countryside Act 1981 is an Act of Parliament in the United Kingdom and was implemented to comply with the Directive 2009/147/EC on the conservation of wild birds...
. 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.
Two
biological pest controlBiological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
agents that show promise in the control of the plant are the
psyllidPsyllids or jumping plant lice are small plant-feeding insects that tend to be very host specific, i.e. they only feed on one plant species or feed on a few related plants...
Aphalara itadoriAphalara itadori, the Japanese knotweed psyllid, is a species of psyllid from Japan which feeds on Japanese knotweed ....
and a
leaf spotLeaf spots are round blemishes found on the leaves of many species of plants, mostly caused by parasitic fungi or bacteria.A typical spot is "zonal", meaning it has a definite edge and often has a darker border. When lots of spots are present, they can grow together and become a blight or a blotch...
fungus from genus
MycosphaerellaMycosphaerella is a genus of sac fungi. With more than 10,000 species, it is the largest genus of plant pathogen fungi....
.
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 honeyMonofloral honey is a type of honey which has a high value in the marketplace because it has a distinctive flavor or other attribute due to its being predominantly from the nectar of one plant species....
, usually called
bamboo honey by northeastern
U.S.The United States of America is a federal constitutional republic comprising fifty states and a federal district...
beekeeperA beekeeper is a person who keeps honey bees for the purposes of securing commodities such as honey, beeswax, pollen, royal jelly; pollinating fruits and vegetables; raising queens and bees for sale to other farmers; and/or for purposes satisfying natural scientific curiosity...
s, like a mild-flavored version of
buckwheatBuckwheat refers to a variety of plants in the dicot family Polygonaceae: the Eurasian genus Fagopyrum, the North American genus Eriogonum, and the Northern Hemisphere genus Fallopia. Either of the latter two may be referred to as "wild buckwheat"...
honey (a related plant also in the Polygonaceae).
The young stems are edible as a spring
vegetableThe noun vegetable usually means an edible plant or part of a plant other than a sweet fruit or seed. This typically means the leaf, stem, or root of a plant....
, with a flavor similar to mild
rhubarbRhubarb is a group of plants that belong to the genus Rheum in the family Polygonaceae. They are herbaceous perennial plants growing from short, thick rhizomes. They have large leaves that are somewhat triangular-shaped with long fleshy petioles...
. 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. Some caution should be exercised when consuming this plant because it, similar to rhubarb, contains
oxalic acidOxalic acid is an organic compound with the formula H2C2O4. This colourless solid is a dicarboxylic acid. In terms of acid strength, it is about 3,000 times stronger than acetic acid. Oxalic acid is a reducing agent and its conjugate base, known as oxalate , is a chelating agent for metal cations...
, which may aggravate conditions such as rheumatism, arthritis, gout, kidney stones or hyperacidity.
Both Japanese knotweed and giant knotweed are important concentrated sources of
resveratrolResveratrol is a stilbenoid, a type of natural phenol, and a phytoalexin produced naturally by several plants when under attack by pathogens such as bacteria or fungi....
, replacing grape byproducts. Many large supplement sources of resveratrol now use Japanese knotweed and use its scientific name in the supplement labels. The plant is useful because of its year-round growth and robustness in different climates.
Japanese knotweed is a concentrated source of
emodinEmodin is a purgative resin, 6-methyl-1,3,8-trihydroxyanthraquinone, from rhubarb, the buckthorn and Japanese Knotweed...
, used as a nutritional supplement to regulate bowel motility. The roots of Japanese knotweed are used in traditional Chinese and Japanese herbal medicines as a natural laxative. The active principle responsible for the laxative effect is emodin, present in its natural form as a complex of its analogs. Emodin has a mild laxative effect in doses of 20 to 50 mg per day.
MethanolMethanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
extracts of the roots of
Polygonum cuspidatum (Polygonaceae), traditionally used in Korea to maintain oral health, were shown to reduce the viability of
Streptococcus mutansStreptococcus mutans is a facultatively aerobic, Gram-positive coccus-shaped bacterium commonly found in the human oral cavity and is a significant contributor to tooth decay.The microbe was first described by J Kilian Clarke in 1924.-Introduction:...
and
Streptococcus sobrinusStreptococcus sobrinus is a Gram-positive, catalase-negative, non-motile, and anaerobic member of the genus Streptococcus.-Pathology:...
as well as inhibit sucrose-dependent adherence, water-insoluble glucan formation, glycolytic acid production and acid tolerance. The authors suggested that inhibitory effects may be mediated by the presence of
alkaloidAlkaloids are a group of naturally occurring chemical compounds that contain mostly basic nitrogen atoms. This group also includes some related compounds with neutral and even weakly acidic properties. Also some synthetic compounds of similar structure are attributed to alkaloids...
s, phenolics,
sterolSterols, also known as steroid alcohols, are a subgroup of the steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol...
s, and
terpeneTerpenes are a large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium. They are often strong smelling and thus may have had a protective...
s in the extract.
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.
Glyphosate is the best active ingredient in herbicide for use on Japanese knotweed as it is ’systemic’; it penetrates through the whole plant and travels to the roots.
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 disposal of the plant material is difficult, governed by law in the UK, where it is classed as controlled waste.
More ecologically friendly means are being tested as an alternative to chemical treatments.
Soil steam sterilizationSoil steam sterilization is a farming technique that sterilizes soil with steam in open fields or greenhouses. Pests of plant cultures such as weeds, bacteria, fungi and viruses are killed through induced hot steam which causes their cell structure to physically degenerate. Biologically, the...
involves injecting steam into contaminated soil in order to kill subterranean plant parts. Research has also been carried out on
MycosphaerellaMycosphaerella is a genus of sac fungi. With more than 10,000 species, it is the largest genus of plant pathogen fungi....
leafspot fungus, which devastates knotweed in its native Japan. Research with
Mycosphaerella has been relatively slow, due to its complex life cycle.
In the UK, 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. Over £150m is spent annually on Japanese knotweed control, and a decision was taken on 9 March 2010 in the UK to release into the wild a Japanese psyllid insect,
Aphalara itadoriAphalara itadori, the Japanese knotweed psyllid, is a species of psyllid from Japan which feeds on Japanese knotweed ....
. Its diet is highly specific to Japanese knotweed and shows good potential for its control
External links