Final Executive Summary March 2008
Project Progress Report Sep 2007
Project Progress Report May 2007
Project Progress Report Dec 2006
This is the home page for the UK-based Japanese knotweed alliance which was established in November 1999 to highlight the problems posed by this invasive weed and to promote its natural control with natural predators. The alliance began with CABI (formerly the International Institute of Biological Control) the Welsh Development Agency, the Environment Agency, National Botanic Garden of Wales and Cornell University but has since grown to include British Waterways, Defra, South West Regional Development Agency, Network Rail and Cornwall County Council as the programme has developed.
Japanese knotweed, a rhizomatous perennial, was introduced from Asia to Europe in the mid-nineteenth century as an ornamental and fodder plant. It is an impressive species, which grows to a height of 2-3 meters, with flecked bamboo-like stems, arching branches and clusters of creamy white flowers appearing late in the season. The orange to brown coloured, woody, dead stems persist erect throughout the winter and new shoots, produced from the extensive rhizome system, grow up amongst these the following spring to form dense thickets. The dead stems and leaf litter decompose very slowly and form a deep organic layer, which prevents native seeds from germinating. Once present at a site, Japanese knotweed increases in area very rapidly and soon forms monoculture stands.
Reproduction is primarily by vegetative regeneration of rhizomes and fresh stems. The rhizome system may extend from a parent plant up to 7 meters laterally and to a depth of 3 metres. Very small fragments of rhizome (as little as 0.7 g) give rise to new plants. Fresh stems produce shoots and roots when buried in a soil medium or floated in water. Stems in water may produce viable plants within 6 days.
Japanese knotweed thrives on disturbance and has been spread by both natural means and by human activity. In riparian areas, high water flows disperse fragments of the plant downstream where new colonies form. In the past, fly-tipping and transportation of soil containing rhizome fragments have been a major cause of spread, particularly in the urban environment. It is only one of two terrestrial plants dealt with by the current version of the UK Wildlife and Countryside Act under which it is illegal to cause it to grow in the wild.
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| Typical JK urban invasion | Regeneration can take place from the tiniest fragment |
Japanese knotweed belongs to the plant family Polygonaceae, the knotweeds. ‘Poly’ meaning many, ‘gony’ from the Greek ‘knee’ meaning jointed.
An artefact of
the history of discovery of this plant is that it has three scientific names:
Reynoutria japonica - described from Japan by the Dutch botanist Houttuyn
in 1777, the name was lost for 125 years.
Polygonum cuspidatum - independent description by Siebold and Zuchharini
in 1845.
Fallopia japonica - a result of the amalgamation of Reynoutria
and Fallopia resulting in the oldest name being used.
The scientific name of Japanese knotweed in current use is Fallopia japonica. Previous scientific names also include Polygonum sieboldii, Polygonum japonicum, Polygonum zuccharini Small, Pleuropterus zuccarinii, Polygonum reynoutria (in USA horticulture trade).
In Japan, the plant is commonly called itadori (meaning 'take away pain'). In its introduced range, common names include Japanese knotweed, Sally rhubarb, donkey rhubarb, gypsy rhubarb, Hancock's curse, Pysen saethwr, Glúineach bhiorach, Mexican bamboo, Japanese bamboo, Japanese fleece-flower, wild rhubarb and crimson beauty.
Whatever its name, it is a native of Japan, N. China, Taiwan and Korea, although it is a Japanese plant that has been introduced to the West. In its introduced range, the species occupies more than half of the 10 km squares used to map plant distribution in the British Isles and is only absent from the Orkney Islands. Its distribution covers much of mainland Europe from southern France and Northern Italy to Norway, many States in the USA from California to Washington and throughout Canada and is increasingly being reported as a nuisance weed in New Zealand and Australia. It is spreading rapidly.
Japanese Knotweed is one of the most extraordinary examples of an invasive plant known. Firstly it is a giant herb, which every Spring grows rapidly to a height of 2 or 3 metres, only to be cut down by the first winter frost and grow afresh the next Spring. It is actually a dioecious plant, which means that you need male and female plants for sexual reproduction to occur, yet in Europe, so far, we only have female plants. Not only is it a single sex, it is also a single clone, as molecular work carried out at the University of Leicester has shown. Given that it must occupy many thousands of hectares in Britain alone (the same clone is also known to occur in continental Europe and North America), in total biomass terms, it is probably the biggest female in the world! The infestation in Swansea has been estimated to weigh 62,000 tonnes, the same as 40 blue whales. It has achieved its wide distribution solely by vegetative reproduction. That is, it has spread by cuttings or from pieces of rhizome, whether deliberately as cultivated plants or as garden discards, or inadvertently, spreading downstream along rivers after flooding events or being spread by road works or site redevelopment involving an infested area.
Just like a film sequel we also have the potential for a further invasion by new improved knotweeds. The hybrid between Japanese Knotweed and Giant Knotweed (F. x bohemica) is now fairly well distributed and is capable of pollinating Japanese Knotweed in a number of localities countrywide. However, in this hybrid between two species, the genetic constitution means that in each pollen grain the chromosomes of the two species are mixed up randomly in different numbers and permutations. Given that a single plant produces many million pollen grains there exists a unique opportunity for the evolution of new knotweed plants better suited to our climate and able to regain the ability to reproduce by seed … a frightening prospect! Thankfully the most common seed is the result of a hybrid between Japanese knotweed and Russian vine, Fallopia baldshuanica (AKA Polygonum aubertii). One might think that the spawn of two such invasive plants would produce a monster but their conflicting life strategies mean that the seedlings rarely if ever establish.
Hybridisation
Implications
Fertility
How
do you know if you have found a hybrid alien?
You
can help
Specific problems caused by Japanese knotweed are:
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| Riparian invasion in south wales | Knotweed breaking through drainage | |
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| Young shoots emerging | Riparian invasion in early season (photograph courtesy of T. Renals) |
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| Overrun
graveyard |
Knotweed
invading a Welsh living room (photographs courtesy of Swansea City Council) |
Japanese knotweed is not an easy plant to control. The extensive underground rhizome system sustains the plant even when top growth is removed. Therefore, the aim of any control programme should be to target the rhizomes. This is best achieved using a chemical treatment. Translocated herbicides such as glyphosate and 2,4-D amine may be used in the UK in riparian areas providing consent is obtained from the Environment Agency. In areas where there is no risk of run-off to watercourses and where no sensitive vegetation (including trees and shrubs) will be affected, the herbicides triclopyr, picloram and imazapyr may be used. The latter three herbicides are persistent in the soil and may delay planting of replacement species. Herbicides are usually applied as a foliar spray but can also be applied directly to target plants using a weed-wiper or herbicide glove. Good results have been achieved by injecting glyphosate into hollow stems immediately after cutting.
When using herbicides, always read the label and follow the manufacturer's instructions. Japanese knotweed requires a number of herbicide treatments over several years before it is completely eradicated. It is important to continue to monitor the treated areas for at least one growing season after treatment to ensure that no new shoots appear. Best results are achieved when foliage is at a maximum i.e the area of leaf through which a foliar herbicide can be absorbed is high and the amount of root is at a minimum. This is commonly agreed to be at or after flowering.
For short term control, Japanese knotweed may be cut using a lopper or brush-cutter. In amenity areas, prevention of invasion from adjacent stands may be achieved by frequent mowing. The young shoots of Japanese knotweed are palatable to sheep, goats, cattle and horses and grazing may be used in suitable situations to keep the plant under control. This will not eradicate Japanese knotweed and the plant will continue to grow once grazing ceases.
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| Nearside bank treated with herbicide | "Bonsai" knotweed post spraying |
WARNING: Japanese knotweed regenerates vegetatively. Very small fragments of rhizome (as little as 0.7 gram) and fresh stem material are able to produce viable shoots and roots. It is an offence in the UK to cause this plant to grow in the wild under the 1981 Wildlife and Countryside Act and any waste material, such as that arising from cutting, mowing or excavation, should be disposed of according to the Environmental Protection Act 1990 (Duty of Care) Regulations. The use of equipment which is likely to result in further spread of Japanese knotweed, such as a flail mower, is strictly advised against. See the ENVIRONMENT AGENCY CODE OF CONDUCT.
The British Government's Non-Native Species Policy Review gives an estimate of the costs to control knotweed countrywide of £1.56 billion which, although unfeasible, gives an indication of the extent of the problem and the high costs associated with control were it to be attempted. Swansea is one of the worst affected areas in the country and as such has the most experience with the costs associated with managing knotweed.
With the increase in trade between countries, many plants and insects arrive in new environments, accidentally or intentionally, without their natural enemies. In the case of plants that is to say that the insects, pathogens and nematodes that inflict damage upon the plant are lost and without these controlling organisms the plant gains an unfair advantage and may become a weed. This is very different to the process of natural arrivals whereby the natural enemies would either arrive with or soon catch up with the plants. Biological control could be viewed as a means of levelling the playing-field by re-introducing some of those natural enemies that keep it in control in its native range.
Of course it would not be very sensible to introduce insects or pathogens that might attack other plants, especially crops or endangered species. Therefore, biocontrol scientists spend considerable time (at least 3 years) studying the host range of any potential agent within a secure quarantine facility according to international protocols. This testing enables them to predict which, if any, other plant species might be at risk. Only once these stringent tests have been carried out and the biological control agent has been shown to be safe is an application to release made.
There have been over 1000 releases of biological control agents (BCA) against weeds in 71 countries using 350 different BCAs in the past 100 years although there has never been a classical programme against a weed in the UK or indeed the EU. Contrast this situation with that in Australia, New Zealand, USA and Canada where biocontrol research is the first line of defence when a new pest species is identified as an apparently unmanageable problem.
Why can’t
we just leave things as they are?
Doing nothing is not an option when it comes to Japanese knotweed as it will
continue to spread unchecked across the country. Even in places where there
is a concerted effort to control the weed it is still spreading. The balance
of nature has been upset by mankind short-circuiting the normal progression
of things. By introducing this plant to a new area without any of the checks
and balances that it had to deal with in its native range, knotweed will continue
to benefit from an unfair advantage.
Isn’t
there a danger of releasing another alien species that may become invasive?
Whilst the biological control agent may not be native to the UK, it is “native”
to knotweed. Only co-evolved natural enemies are considered and these have normally
sacrificed their ability to feed on other species to specialise on the target
weed. By applying standard testing procedures to a selected agent it is possible
to demonstrate that the risk to UK native biodiversity or crops is negligible.
The care taken prior to releasing a biological control contrasts sharply with
the wholesale importation of alien species, either as pets or garden plants
and their pests, or as stowaways within compost, timber, ballast water and other
materials.
Is there
an alternative?
The only current alternative control method requires the widespread and long-term
use of herbicides and since knotweed is still in a rapid expansion phase this
could only mean increased chemical use rather than the most stated Government
goal of reduced chemical use. Unfortunately, experience shows that chemical
treatment can just force knotweed into dormancy. Many knotweed areas are near
watercourses, so there is a risk of pesticide contamination to the stream or
river but often attempts to deal with knotweed by physical means actually exacerbate
the problem. A successful biological control approach will greatly reduce the
need for these sprays.
Is this
like GM?
No. Genetic modification involves human intervention to provide an organism
with certain genes that code for desirable traits. In the case of classical
biological “Mother Nature” has done the modifying for us through
the process of evolution. A biocontrol release does nothing to change the naturalness
of the organism, it simply allows a natural balance to be restored to the environment.
How can it
be that they only attack one plant?
Most insects and pathogens are monophagous, that is to say they will only attack
one species of plant. This is not as surprising as it seems since many endangered
insects are under threat because their only host plant or its habitat has become
rare. These organisms have spent hundreds and thousands of years evolving to
overcome the defences of their food plant and during this time they have been
forced to become restricted to this plant to complete their lifecycle. Of course
some insects and pathogens will eat all kinds of plants but these would not
be under consideration.
| How
can one tiny beetle or fungus do the job? Well on its own one tiny beetle will not have much effect but once it has reproduced for a few seasons millions of beetles are a force to be reckoned with. Although it is not normal for a population of a species to explode it is more likely with biological control agents. Once they have had their own natural enemies removed then they will have lost their controlling agents, just like the weed did. Rather than the ephemeral effects of chemicals, the beetles and fungi will continually be debilitating the knotweed and preventing it from competing as strongly.Remember the effect of Dutch Elm disease? This was caused by a fungus, carried by a beetle. Another more current example is that of the Azolla weevil. |
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Plant stripped by leaf feeding insect |
What will it
eat when it has eaten all of the weed?
A biological control agent is not doing itself any favours if it eradicates
its only host plant since it will not be able to utilise any others. What normally
happens is that there will be considerable fluctuations in the pest and predator
populations until an equilibrium is reached which pushes the weed population
below the necessary threshold level. Here it will stay indefinitely, providing
control forever without any further cost. Because it is specific to knotweed,
it cannot move onto another plant, once it has controlled the knotweed. There
is no more risk of a knotweed biological control agent switching to another
food plant, than there is of apple coddling moth eating your roses!
What
about the cane toad?
The cane toad Bufo marinus, was introduced to Australia by the sugar cane industry
in 1935 in an ill-judged attempt to control pest beetles. Thousands of toads
were released without any host specificity testing and not only failed to control
the beetle but turned their carnivorous attention to anything that moved, becoming
a problem themselves. Although carried out in the name of biocontrol, today’s
practitioners consider this sorry event to have been an act of madness and the
use of such polyphagous (generalist) vertebrate agents would never be attempted
or indeed allowed today.
Does it work
?
There have been many notable successes in biological weed control not least
the example of the weevil Cyrtobagous salviniae against Salvinia weed
in Sri Lanka. The plant was introduced into the country during the second world
war to prevent the enemy aircraft from identifying waterways and it did the
job so well that almost all waterbodies in the country were affected. The weevil
was released in 1986 and within 4 years it had destroyed around 80% of weed
infestations. Since its discovery Cyrtobagous has been a successful control
agent against this weed in more than 10 tropical countries around the world
and is still working today.
Other examples of current or potential successes are:
Rubbervine
Weed
Leafy
Spurge
Alligator
Weed
Purple
Loosetrife
What are the advantages of classical biological control?
What are the disadvantages of classical biological control?
Progress so far
Phase 1 This phase of the project was completed at the end
of 2000. Funding from the Welsh Development Agency and the United States Department
of Agriculture Forest Service enabled a team of British scientists from CABI
Bioscience and Leicester University to carry out an initial survey
in Japan in August 2000. Thanks to the considerable assistance provided by Japanese
scientists, it was possible to visit 31 sites across 9 prefectures at altitudes
ranging from sea level to 1550m.a.s.l. A total of 3400km were covered by the
survey team in Japan.
This Phase revealed that the plant was not as prolific as it is in the west and is obviously under considerable stress thanks to the efforts of the multitude of associated natural enemies. Amongst the insects and fungi found damaging virtually every plant, some appeared promising from the outset and it was possible to collect many of these natural enemies for identification purposes and initial host range testing in UK quarantine. During the early studies a sawfly was found to attack other UK Polygonaceae in the stringent laboratory experiments and was instantly rejected as a potential agent.
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Japanese
collaborators from Kyushu University (left) |
Phase 2
The full 4 year programme finally began in May 2003 with a survey in Japan to
reinforce links with collaborators and further our knowledge of natural enemies
in the field. Thanks to the financial contribution and guidance of the consortium
of sponsors including the Welsh Development Agency,
South West of England Regional Development
Agency, Environment Agency,
DEFRA, Network
Rail, British Waterways
under the co-ordination of Cornwall County
Council the programme is in full swing.
This project is allowing excellent collaboration between UK scientists and Japanese
scientists and would not be able to proceed without the input from the Biological
Control Laboratory of the University of Kyushu in Fukuoka.
Further surveys were carried out in 2004 and 2005 at different times in the growing season, to maximise chances of finding all life stages of potential agents. Work has concentrated on identifying the agents and prioritising them based on their behaviour in Japan and likely impact/host range. A comprehensive test plant list of over 80 species ranging from closely related species to valuable crop plants and rare natives has been drawn up and these plants will be used to determine how specific the insect or fungus is and therefore how safe any future release would be. This work is all being carried out in strict quarantine. So far a number of agents have been rejected and our efforts are currently focused on two insect species, a stem boring Lixus weevil and a sap-sucking Aphalara psyllid, as well as a Mycosphaerella leafspot fungus. These agents appear to be restricted to Japanese knotweed in its native range and thorough testing will reveal their true host range but other agents are yet to be dismissed. Our Japanese collaborators at the University of Kyushu are continuing to observe the plant and its natural enemies in the field in Japan, which will ensure that nothing is missed.
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Some of the insect and fungal agents under consideration |
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| Leafspot fungus | Lixus weevil | Aphalara psyllid |
Will
biocontrol work for Japanese knotweed? Most of the natural enemies from Asia are not found here, indeed very few insects or pathogens are ever found on knotweed stands in the UK. Some of the Japanese agents proving to be highly specific. In summary there is every reason to believe that Japanese knotweed is a suitable target for biological control and that this approach will work as it has for so many weeds in the past. |
 Plant killed by natural enemies in laboratory |
How can I find out more about biological control?
Below is a list of websites dealing with biological control of weeds.
CABI
Biocontrol Position Statement
Landcare
Research, New Zeland
USDA
Cornell
University's Biological Control: a Guide to Natural Enemies in North America
Biological Control of Weeds X International Symposium
Biological
Control Virtual Information Center
EU Giant Hogweed
Project
Please contact
us to recommend other web sites on this subject.
Cornwall
County Council (which has all the links you would need for knotweed in the
UK)
The
Nature Conservancy Element Stewardship Abstract
Cornwall
Knotweed Forum
Tweed
Invasives Project
Devon
Knotweed Forum
Japanese
knotweed in the Eastern USA
Invasive
Plant Atlas of New England
Japanese
knotweed photos and recipes
Environment Agency Knotweed Code of Practice
To view the film 'Knotweed' made by the Whatcom County Noxious Weed Board and the City of Bellingham, Washington in an effort to educate the public, click here.
Plus you should also see the Japanese knotweed manual by Child & Wade published by Packard Publishing ISBN 1 85341 127 2
Disclaimer
This publication may be of assistance to you but CABI Bioscience and
the Japanese Knotweed Alliance do not guarantee that the publication is without
flaw of any kind or is wholly appropriate for your particular purposes and therefore
disclaims all liability for any error, loss or other consequence which may arise
from you relying on any information in this publication.
