Japanese knotweed

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Japanese knotweed
Japanese knotweed (Fallopia japonica), typical population

Japanese knotweed ( Fallopia japonica ), typical population

Systematics
Eudicotyledons
Nuclear eudicotyledons
Order : Clove-like (Caryophyllales)
Family : Knotweed family (Polygonaceae)
Genre : Winged knotweed ( fallopia )
Type : Japanese knotweed
Scientific name
Fallopia japonica
( Houtt. ) Ronse Decr.

The Japanese knotweed ( Fallopia japonica ( Houtt. ) Ronse Decr. , Synonyms : Reynoutria japonica . Houtt , Polygonum cuspidatum . Siebold & Zucc ), also Kamchatka knotweed or short Japanese Knotweed called, is a species of the genus creepers or fallopia ( Fallopia ) resp. Knotweed ( Reynoutria ) within the knotweed family (Polygonaceae). In Europe and North America, this type of plant is one of those neophytes that are rated as problematic, undesirable invasive plants ("pest plants").

description

Illustration from Curtis's Botanical Magazine , Plate 6503
Fallopia japonica with alternate leaves: the stem forms a zigzag line and inflorescences in the upper, light-close leaf axils
Flowers of a female plant
Winged fruits
Habit of a male plant that is just blooming

Appearance

The Japanese knotweed is a very fast-growing (rampant), deciduous, perennial herbaceous plant . As a survival organ, it forms rhizomes , which often create dense, extensive stands. In spring it drives out of its rhizomes ("root stocks", creeping shoots), often nests on "rhizome heads", new stems ("ramets"), which under favorable conditions reach a height of 3 to 4 meters within a few weeks, whereby the plant one Growth can reach 10 to 30 centimeters per day. The initially upright, but soon oblique to horizontal overhanging stems are hollow. Because at the height of summer the tops of the uncut shoots tilt horizontally and the leaves spread out horizontally, the soil under such dense stands is so shaded that even grass growth dies. In the winter months, the bare topsoil between the leafless tubular stems can be rinsed off extensively during heavy rainfall and fill the stream bed. At the Harmersbach in the central Black Forest, this led to millions in damage during the “Christmas flood” in 1991, because the raging floods of the brook that overflowed the banks of the river washed away the streets and tore away bridges.

In the late year the plant moves in and the leaves turn yellow, with the first frost , all parts of the plant above ground die. The widely branching, soon and from year to year more woody rhizomes survive the winter without any problems. Although they crawl largely horizontally, they often reach up to 2 m deep into the ground. There they sometimes also seem to form bulbous storage organs.

leaf

The alternate arranged on the stem leaves are divided into petiole and leaf blade and 5 to 20 centimeters long. The simple, egg-shaped, almost leathery leaf blade with a length of up to 12, rarely up to 18 centimeters and a width of up to 8, rarely up to 13 centimeters wide, has a right-angled blade base and a narrow tip ("trickle tip"). The short hairs on the leaf veins on the underside of the leaf can hardly be seen without a magnifying glass.

Inflorescence and flower

The Japanese knotweed is dioecious separately sexed ( diocesan ). In August, the Japanese knotweed begins to develop the inflorescences . The functionally unisexual flowers contain five whitish bracts and either one ovary with three fringed stigmas or eight stamens .

Chromosome number

The number of chromosomes is 2n = 88.

Origin and history of spread in Europe

The Japanese knotweed is native to China , Korea and Japan . This plant species was brought to Europe by Philipp Franz von Siebold around 1825 as an ornamental and fodder plant and was also introduced to the USA in the 19th century . The Japanese knotweed is one of the so-called hemerochoric plants that were specifically introduced ( ethelochor ). The Japanese knotweed was also specifically cultivated in forestry . It should serve as a grazing plant for red deer as well as a cover plant for pheasants . The Japanese knotweed is not accepted as a grazing plant and is not very suitable as a cover plant due to the leaf fall in late autumn. The beekeepers played a large part in its expansion , as the Japanese knotweed is an excellent bee pasture in early autumn .

In the 21st century, the Japanese knotweed can be found in Central Europe both in gardens , used as a privacy screen because of its fast and high growth, and also growing wild in the open. In Switzerland, this plant species can be found in all regions except the Upper Engadine . There he was added to the black list of invasive neophytes in Switzerland and subject to the release ordinance.

Location and socialization

The Japanese knotweed thrives almost everywhere in Central Europe; especially on wet, near groundwater, even temporarily flooded, nutrient-rich, mostly low-lime, clayey gravel or gravel soils. It is an intolerant pioneer plant in the associations of Alno-Ulmion (alder-ash floodplain forests) or Salicion albae (softwood floodplain) and forms its own societies in the Artemisietea class (mugwort societies). In the Allgäu Alps in Bavaria, it rises at the southeastern foot of the Grünten to an altitude of 1000 meters; in the southern Black Forest in Multen am Belchen for eight decades at such an altitude.

Propagation strategy

"Rameten-Nest"

In the regions in which the Japanese knotweed is a neophyte , generative reproduction via seeds hardly plays a role. Rather, clonal, vegetative reproduction dominates . Below the soil surface, in several layers on top of one another, this plant forms horizontal rhizomes ("creeping shoots"). The Japanese knotweed can very quickly form extensive and very dense stocks. In this way they quickly colonize a new habitat, for example with garden waste or construction site excavation. Parts of rhizomes are also carried away by floods . This perennial thrives along the sunny banks of a stream . Genetically uniform, because clonal, unisexual Japanese knotweed stocks of a good 1 km in length, which therefore only consist of male or purely female ramets, can be seen in some rivers; so z. B. in Alsace along the river Fecht. The lower sections of the stem can also take root if they are flooded or covered by soil.

Damage as an invasive neophyte

Already many years old, woody rhizome of Fallopia japonica
This old locomotive in Beekbergen (Netherlands) is overgrown with knotweed. A few years ago this place was still free of knotweed, see Google Maps .

The Japanese knotweed is now widespread in 42 US states and six Canadian provinces as well as many European countries, where it can largely displace other species and thus endanger biodiversity . Also in Australia and New Zealand this species is classified as a nuisance ("nuisance").

The Japanese knotweed is problematic in nature reserves (especially floodplains and brooks ) because it successfully asserts itself against the native flora due to its extraordinary vigor and robustness . In Austria, it penetrates through loose material into the sensitive ecological systems of the alpine pastures at altitudes of up to 1500 meters.

The Japanese knotweed is available as a garden plant because of its particular resilience and rapid growth. The Central Horticultural Association , however, recommends avoiding fallopia species. The sale, propagation, planting and toleration of Japanese knotweed are prohibited in Switzerland, as is the case in Great Britain. In Germany, application is prohibited under the Federal Nature Conservation Act.

relative

Somewhat rarer are the Sakhalin knotweed ( Fallopia sachalinensis ), which comes from the island of Sakhalin and is similar to it , which is cultivated in a similar way and also grows wild. This differs from the Japanese knotweed in that it is taller (up to 4.3 meters), larger, up to 30 centimeters long leaves with a clearly heart-shaped base and greenish-white inflorescences.

The hybrid of these two species is just as common : Fallopia × bohemica (Syn .: Reynoutria × bohemica , Reynoutria × vivax ). The easiest way to determine it is via the hairiness of the leaves: Reynoutria japonica : leaves glabrous (or hairiness not visible to the naked eye); Reynoutria sachalinensis : leaf blade hairy underneath; Fallopia × bohemica : only the leaf veins are visibly hairy.

Combat

Attempt to combat by covering with "black film"

The control of the Japanese knotweed is difficult due to its physiognomy and rhizome formation. The laborious tearing up of the creep shoots is hardly practicable after they have become lignified and because of their fragility. Until now it was assumed that by mowing the underground parts of the sprouts at least once a month, the energy reserves would gradually be depleted and the plants would "starve" after several years of efforts. However, more recent studies could not prove any long-term success even after mowing 20 times a year. Rather, there is a risk that small parts of the plant (e.g. rizome fragments weighing only 0.06 g) will further spread the knotweed. It could also be proven that the rhizomes react with stronger lateral growth when the above-ground parts of the plant are mowed. In order to prevent further spread, parts of plants must not be disposed of in the organic waste bin, especially if they have " sleeping eyes ". In addition to the labor-intensive mechanical processes, knotweed is controlled with broad spectrum herbicides such as Roundup . The selective application of Roundup after mowing into the hollow lower stem segments of the plant has proven to be effective. In practice, large-scale applications as well as partial applications of chemical weed control agents are described. Targeted injection is always preferable to large-area application, also because of the thin layer of wax on leaves and stems. The injection must usually be given every 4 to 6 weeks, preferably in the middle of the year (June / July). Around 90% of the stock is destroyed in the first year. Subsequent observation and control over the next two years is, however, essential to ensure lasting success.

As an alternative to chemistry, other processes have been tried, such as B. in the regional council of Freiburg steaming , in which the problematic underground knot parts with hot steam z. T. were killed. The disadvantage of this method is that soil organisms are also killed. In the city forest of Bad Vilbel near Frankfurt am Main, attempts have been made since March 2013 to prevent the spread by covering large areas with black plastic sheeting , which takes away the light from the emerging stems. This reduces the risk of unintentional damage. An alternative to chemical control is the release of the Japanese small leaf flea Aphalara itadori , begun in April 2010 by the British research institute Cabi . In laboratory tests, this psyllid species has shown no appetite for other Central European plants and is to be released in the UK on a trial basis in 3 to 6 places outdoors . Reports of successes are pending.

Grazing with Heidschnucken was carried out in Baden-Württemberg on the Kinzig in 1992. It did not have any lasting success. In Carinthia, an attempt was made from spring 2014 to graze the plants with goats.

use

The young shoots up to 20 cm high can be prepared as vegetables. When they are very young, they can even be eaten raw.

In China and Japan the root is used medicinally.

All parts of the plant contain the secondary plant substance trans- resveratrol , which is being tested for numerous possible therapeutic benefits. Resveratrol has effects as a phytoestrogen , among other things . The plant has been used in its native Japan for centuries for medicinal teas, which, like the plant itself, are called "Itadori". Resveratrol is considered to be the most likely active ingredient in tea. Although the resveratrol content in the plant is several orders of magnitude higher than in red grapes (another, much studied source of resveratrol), the content in tea was no higher than in red wine; this is attributed to the fact that it is heavily diluted in the aqueous tea extract.

The stems are suitable for making flutes , both for longitudinal and transverse flutes and pan flutes .

Knotweed as a nesting location for songbirds

Up to 2019, scientific studies on the use of knotweed as a nesting location for songbirds had only been published in four cases in Europe. In knotweed nests were Sumpfrohrsänger , reed warblers , Dunnock , Linnet , backed Shrike , Yellowhammer , Blackbird , Blackcap and garden warbler found. A young cuckoo was found in a marsh warbler nest in knotweed . In Japan, they found nests of China warbler (Acrocephalus orientalis), brewing warbler (Acrocephalus bistrigiceps) Riesenschwirl ( Locustella fasciolata ), Siberian Rubythroat and mask Bunting ( Emberiza spodocephala ) in it. Because the knotweed is used as a nest location, control measures should actually only take place outside of the breeding season so that breeds of protected songbirds are not destroyed. The seed is eaten by various species of birds.

swell

literature

To control measures:

  • Paper of the Reynoutria workshop 2006: REYNOUTRIA 2006: Ecology, impact on the environment and control of invasive knotweed species - SYNTHESIS. In it u. a. Esther Gerber (CABI Bioscience CH): Invasive Knotweed Species in Europe: Biology and Ecological Impact; Trevor Renals (Environment Agency, UK): Control of Reynoutria spp. in Cornwall, GB - a partnership approach and Hella Heuer (City of Freiburg im Breisgau): 15 years of knotweed control in Freiburg im Breisgau - what have we learned? ( PDF )

Individual evidence

  1. ↑ a b c Erich Oberdorfer : Plant-sociological excursion flora for Germany and neighboring areas . With the collaboration of Angelika Schwabe and Theo Müller. 8th, heavily revised and expanded edition. Eugen Ulmer, Stuttgart (Hohenheim) 2001, ISBN 3-8001-3131-5 , pp.  338-339 .
  2. ↑ SECB: Invasive Alien Plants , page 6. ( Memento of the original from February 23, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.efbs.admin.ch
  3. ^ Federal Office for the Environment FOEN: Invasive Alien Species . ( admin.ch [accessed on August 6, 2019]).
  4. ↑ S. Buholzer, M. Nobis, N. Schoenenberger, S. Rometsch: List of the alien invasive plants of Switzerland . Ed .: Infoflora. ( infoflora.ch [accessed on August 6, 2019]).
  5. ↑ Erhard Dörr, Wolfgang Lippert : Flora of the Allgäu and its surroundings. Volume 1, IHW, Eching 2001, ISBN 3-930167-50-6 , pp. 455-456.
  6. ↑ JH Brock, PM Wade: Regeneration of Japanese knotweed (Fallopia japonica) rhizomes and stems: observations from greenhouse trails. In: Proceedings 9th international Symposium on the Biology of Weeds. Dijon, France, 1992, pp. 85-94.
  7. ↑ USDA USDA data sheet , accessed Aug. 12, 2007
  8. ↑ Weblinks: Japanese Knotweed Alliance
  9. ↑ Archived copy ( Memento of the original dated August 4, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.g-net.de
  10. ↑ Swiss Release Ordinance (FrSV), p. 37. (PDF file; 239 kB)
  11. ^ Wildlife Act 1981
  12. ↑ Andreas Braun: Fight the knotweed. Bach patent conference in Freiburg im Breisgau, October 27, 2007, the knotweed
  13. ↑ Daniel Jones, Mike S. Fowler, Sophie Hocking & Daniel Eastwood (2020): Please don't mow the Japanese knotweed! NeoBiota 60: 19-23. doi: 10.3897 / neobiota.60.56935
  14. ↑ Ursula Bollens: Control of the Japanese knotweed. Literature review and recommendations for railway systems. BUWAL Environment Materials 192, Bern 2005
  15. ↑ Dampening Report , October 3, 2009
  16. ↑ Le Monde 66, No. 20529 of March 12, 2010, p. 4th
  17. ↑ Süddeutsche Zeitung v. March 10, 2010, p. 16 ( Online ( Memento of the original from April 12, 2010 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this note. ) @1@ 2Template: Webachiv / IABot / www.sueddeutsche.de
  18. ↑ Central Specialist Service Water, Soil Waste at the State Agency for the Environment Baden-Württemberg: Handbook Water 2. Control of Japanese knotweed on flowing waters. 1. Trial of selected measures. Published by the State Institute for Environmental Protection, 1994.
  19. ^ Badische Zeitung: Recipes against the pest plants - Schopfheim. Retrieved July 21, 2020 .
  20. ^ Weeds: Animal experiment at the ÖBB, report by ORF Carinthia , June 25, 2014
  21. ↑ Rita Helene: Japanese knotweed. Retrieved October 25, 2019 .
  22. ↑ Franz Bucar: Phytoestrogens in Plants: with special reference to isoflavone. Chapter 2 in Victor R. Preedy (editor): Isoflavones: Chemistry, Analysis, Function and Effects. Food and nutritional components in focus, Vol. 5. The Royal Society of Chemistry, London, ISBN 978-1-84973-419-6 .
  23. ↑ Jennifer Burns, Takao Yokota, Hiroshi Ashihara, Michael EJ Lean, Alan Crozier (2002): Plant Foods and Herbal Sources of Resveratrol. Journal of Agricultural and Food Chemistry 50: 3337-3340. doi: 10.1021 / jf0112973
  24. ↑ Instructions for flutes made of knotweed , accessed on December 13, 2015
  25. ↑ Jens Hering: Plea for a hated neophyte: Knotweed stocks Fallopia spp. as an important nest location for songbirds . Vogelwarte 57, 2019: 99–114.

Web links

Commons : Japanese knotweed ( Fallopia japonica )  - Collection of images, videos and audio files