Identification There are six principal identifiers of Japanese knotweed: Leaf: midgreen, shieldshaped (pointed tip with a straight edge along the top). Leaves can vary in size. Petiole (leaf stem): distinctive zigzag, due to leaves growing alternately along the stem. Often pink/purple in colour. Figure 1 Japanese knotweed leaf and petiole Stem: bamboolike, hollow, jointed. Green, often with a pink/purple speckle. Crown: a knotty mass in the ground at the foot of stems on mature knotweed plants, often partially visible above ground. The most regenerative part of the plant. Thick, fibrous roots and rhizomes grow from the crowns. Page 1.
Page 2.
Figure 2 Japanese knotweed stems and exposed crown (glove indicates scale) Rhizome: an underground stem system that can spread several metres in any direction. In mature plants, rhizomes grow from the crowns with many pushing up to the surface as new shoots. Internally rhizome is orange, rather like a carrot, though can be bleached white when very young. Wispy, fibrous roots grow from the surface of mature rhizomes. Figure 3 Japanese knotweed rhizome (crosssection) Flower: small, white, fivepetalled, appearing in clusters in late August. Persist until October/November. Page 3.
Figure 4 Japanese knotweed flower Different types of knotweed in the UK When one refers to knotweed in the UK one is often referring to Japanese knotweed (Fallopia japonica). This is the most common species of knotweed in the UK but it is not the only one; below is a brief description of the other knotweeds found in the UK. Please note: When 'knotweed' and 'Japanese knotweed' are referred to throughout this section the inclusion of the species below should be inferred. Giant knotweed (Fallopia sachalinensis) This originates from Sakhalin Island, Korea, northern Japan, and the Kurile Islands. It was introduced to Britain sometime during the late 1860s but is less widely distributed than Page 4.
Japanese knotweed. It is a much taller plant (up to 45 metres tall) and has much larger, elongated heartshaped leaves. It possesses the same zigzag on the stems, due to the alternate placing of the leaves, but the bamboolike stems are more greenishbrown in colour. New growth tends to begin later in the spring than other knotweeds, though flowers still appear late summer or early autumn. The flowers themselves are greenishwhite in colour and produced in dense clusters. Rhizomes are often more creamy in colour than the orange of Japanese knotweed. Figure 5 Giant knotweed Bohemica (Fallopia x bohemica) Otherwise known as bohemian knotweed, hybrid knotweed or the somewhat longwinded Fallopia japonica var. japonica x Fallopia sachalinensis, this is a hybrid formed by the pollination of Japanese knotweed by Giant knotweed. Whereas most such hybrids are shortlived or have little longterm effect on their local environment, bohemica is proving to be highly successful and occurrences of this plant are increasing across Europe and the UK. Not Page 5.
only is it on the rise, but it has proved to be much more resistant to herbicides than other knotweeds. Bohemica was only recognised as a separate species in 1983, but it is clear that it had been flourishing for at least a century prior to this. It grows to a similar height to Japanese knotweed, though stems are often thicker and leaves are larger, darker green, more crinkly in texture (especially around the edges) and heartshaped instead of shieldshaped. Rhizomes often have less colour internally than Japanese knotweed and mature bohemica plants have been discovered with an absence of crown. Flowers appear in late summer, are creamywhite and are produced in denselypacked clusters. Figure 6 Bohemica Himalayan knotweed (Persicaria wallichii) This originates from the Himalayan region of Asia. It is one of the least common knotweeds found in the UK, and does not particularly resemble such knotweeds as Japanese, Giant, Bohemica or Dwarf. It grows to an average height of 1.82 metres and the stems are quite different to other knotweeds. They are not particularly bamboolike and although they zigzag this is caused by node points where groups of leaf stems branch from rather than simple alternate leaves. Brown sheaths can be found at these node points and the stems are covered Page 6.
in visible white hairs. Leaves are variable but tend to be long and thin, tapering to a point, and slightly crinkled along the edges. Flowers are small, white or pale pink with yellow centres and appear in upright loose clusters on the ends of the stems in midsummer. Figure 7 Himalayan knotweed Dwarf Japanese knotweed (Fallopia japonica var. 'Compacta') This is a much smaller version of Japanese knotweed, growing no more than 70 centimetres to one metre in height on average. Leaves and flowers have some distinct differences from standard Japanese knotweed, with the leaves being darker green and more variable in shape. The leaves have a leathery texture and are usually concave, with crinkled edges curling upwards. Flowers, appearing late summer in tightly packed upright spikes, are usually pale pink or white, maturing to a dark pink or red. Page 7.
Figure 8 Dwarf knotweed Lesser knotweed (Persicaria campanulata) This originates from North India and southwest China. Not particularly widespread in the UK, it bears little resemblance to the main knotweed species. It grows up to 6090 centimetres tall and has pinkgreen, tubular, crooked stems that are often free of any leaves on the bottom twothirds. Leaves are variable, but long and pointed. They grow at approximately 90? to t e stems, are dark to midgreen and have a distinctive 'herringbone' pattern on them. T e undersides of the leaves are lighter in colour and covered in white hairs, giving them a feltli e appearance. Flowers are tiny, bellshaped and appear in midsummer. They are white or pa e pink in colour and are produced loosely along short, upright spikes. Page 8.
Figure 9 Lesser knotweed Conollyana (Fallopia x conollyana) This is the rarest of knotweeds in the UK. It is another hybrid species, produced by the pollination of Japanese knotweed by a nonknotweed: Russian vine (Fallopia baldschuanica). It tends to be shortlived in the UK, though has been recorded more commonly in Europe. It has an elongated, pointed leaf with a straight back edge. Page 9.
Figure 10 Conollyana Why it is a problem The greatest impact knotweed has on the human environment is the way it can grow through manmade structures, resulting in irreparable damage. Thin new shoots, with the vigour to grow quickly due to their access to the extensive nutrient store contained in the rhizomes and crowns of the mother plant, can exploit the smallest of weaknesses in tarmac, concrete, paving, mortar, etc. Once the knotweed shoots have penetrated the structure (e.g. walls, drainage systems, hard landscapes, etc.) subsequent growth will increase the size of the structural fault and gradually push the whole edifice apart. Horizontal structures, such as paving, will be lifted by knotweed, causing similar damage to that caused by tree roots but in a much shorter period of time. Page 10.
Japanese knotweed will dominate any area where it is allowed to establish itself. In the Far East it is not seen as a problematic species, since a number of plant competitors and a range of natural insect and fungi predators keep it firmly in check. In the UK, Europe, North America and Australasia it has no competition or predators at all (though this may change, see FAQs) and this is why it is thriving usually at the expense of native species, which are simply 'shaded out' by knotweed's thick leaf canopy. Knotweed's predilection for moist conditions means it can be found growing alongside rivers and streams where it restricts access to river environments and increases the risk of flooding by trapping sediment and clogging waterways with leaf and stem debris. Japanese knotweed can regenerate from tiny fragments of itself. Whilst stem and leaf regeneration have been recorded, rhizome and crown regeneration are more common. A fragment of rhizome the size of a paperclip can give rise to a new plant. Dos and don'ts As knotweed can regenerate from small fragments of itself, avoid any practice that will break up and spread knotweed material around the site of origin. If removing knotweed material from its site of origin be mindful of duty of care legislation and dispose of the material correctly. Do not: flail, strim or chip live knotweed; scrape a development site until it has been verified that it is free of knotweed; cut, pull or compost live knotweed stems (see frequently asked questions ); add knotweed material however small to standard green waste or take to a local amenity tip (see frequently asked questions ); allow knotweed material to leave site unless it is properly bagged or sheeted to prevent the risk of any spillage en route to landfill; fly tip material containing knotweed; or leave knotweed unchecked and allow it to spread into someone else's property. verify if your property contains knotweed particularly if you are planning to conduct any kind of construction/development works; cordon off the knotweed areas if they are likely to be disturbed by members of the public, site staff, site vehicles, etc.; begin treating knotweed as soon as it is identified; treat knotweed onsite if possible otherwise ensure all offsite disposal takes place to a licensed landfill facility; and consult an expert if in doubt. Do: If it is a development site, you are strongly recommended to implement a knotweed management plan (KMP) and ensure it is followed closely by all personnel connected with the site. More information on this can be found within the Environment Agency's Knotweed Code of Practice. Page 11.
Control and eradication How difficult is it? Many people regard ridding themselves of knotweed as virtually impossible and equate the plant as somewhat akin to a Triffid. This is simply not the case, though the perception has allowed a few unscrupulous contractors to pile on the sensationalist scare mongering in their sales pitches to panic punters into employing their services. In truth, knotweed treatment can be pretty straightforward. The reason treatment is perceived as being much more complicated than it is stems from the fact that there are certain truths about knotweed treatment that clients do not want to hear. To begin with, 100% eradication of knotweed cannot ever be guaranteed. With knotweed able to regenerate from such tiny parts of itself and with it having such a long dormancy threshold, it is impossible to say that all of the knotweed is dead on a site just because there hasn't been any new growth for a year or two. Some companies have tried to get around this by offering viability tests on knotweed material removed from the ground. Whilst this can produce some assurance it is still far removed from a 100% guarantee. Viability tests depend on random sampling and therefore there is always the risk that one of the pieces of rhizome that wasn't tested is the one that's still alive. One can make strong assumptions from lack of regrowth and viability test results but one can never categorically state that knotweed is 100% eradicated. Be wary of anyone who claims otherwise. The next truth clients do not want to hear is that knotweed treatment takes time unless you are prepared to spend a substantial amount of money. Everyone in the knotweed industry is chasing the ideal of a 100% eradication method achievable within a single growing season because this is what their clients particularly the construction industry are seeking. Many claim to have found it, though one should always remember the phrase 'buyer beware': knotweed can react against being hit too hard with herbicides in too short a period of time by going into dormancy, which can produce misleading results and lack of new growth for a season or two. The options Because there are now so many companies 'jumping on the knotweed bandwagon' so to speak, there are a myriad of treatment methods offered in the marketplace. In essence, though, they boil down to variations on the following four methods: excavation; mechanical disturbance; root barrier; and/or herbicide control. Excavation This involves digging an extremely large hole in the ground and removing all knotweed material. The size of hole will vary, as any contractor worth their salt should be able to tailor the dig out to the actual spread of the knotweed by chasing out the rhizomes, rather than excavating a hole to set dimensions and resulting in clean soil being needlessly removed. Once the knotweed has been fully excavated, there are a number of options as to what to do with it. The traditional method has been to dispose of it as landfill the socalled 'dig and dump' method but this has been recognised as unsustainable (not to mention expensive) and is regarded by the Environment Agency in their Knotweed Code of Practice as something of a Page 12.
last resort. Onsite treatments of excavated material can include burying it in a cell burial (enveloped in root barrier and with the top of the cell no less than two metres below finished ground level) or relocating it to another part of the site where there is more time to treat it. Mechanical disturbance This is not an eradication method in itself, but involves weakening the rhizome of the plant by cutting it up into smaller pieces and pulling some of the deeper rhizomes closer to the surface. This makes the knotweed more susceptible to other forms of treatment. Root barriers Barriers are used to contain knotweed that, for one reason or another, cannot practically be excavated (e.g. rhizomes that spread across boundaries). It is important to use specialist root barrier membranes for this as standard plastic sheets are not strong enough to prevent knotweed growth simply ripping straight through them. Root barriers should be used in combination with other treatment methods, as all they do is contain the knotweed rather than kill it. Herbicide control This involves the regular use of herbicides, usually over a few growing seasons, to gradually kill off the plant. Some contractors like to exclusively use residual herbicides, as they are stronger and keep working in the soil for months even years after initial application. However, be aware that residual herbicides can create a good initial result by killing off the knotweed closer to the surface, but they can send the rest of the knotweed into dormancy where it will wait out the treatment and emerge years later. The most commonly used nonresidual herbicide is one containing the active ingredient glyphosate. This chemical will take longer to stop the emergence of any new growth (usually 34 years), but it is more likely to have a lasting result. For chemical advice, consult a BASIS qualified advisor. These four methods are often used in conjunction with each other. For example, the reason for relocating knotweed to another section of the site will be to allow the stockpile to be treated under a herbicide programme. The shallower the stockpile the more effective the programme will be, as a shallow stockpile encourages all of the rhizome to grow rather than allowing some to remain buried and dormant. Mechanical disturbance is also often used in tandem with a herbicide treatment programme to shorten the overall duration. Root barriers are used to encompass a burial cell and they can also be used to horizontally 'cap' a partial excavation (knotweed is excavated to a certain level and the remaining rhizomes are left where they are and 'capped' to prevent them reemerging). The permutations can be many and varied. Timescales for treatment Timescales vary according to the control method chosen. Generally speaking, the more time there is available for treatment, the more options are available and the less money it will cost. For Japanese knotweed, the basic timescales are: excavation and removal to landfill a few weeks at most; excavation and burial on site a few weeks at most; excavation and relocation a few weeks at most; herbicidal treatment of relocated knotweed 24 growing seasons; cultivation and herbicidal treatment 24 growing seasons; and herbicidal treatment programme 34 years (average). Page 13.
For example, a less mature stand of knotweed will take less time to treat with herbicide than a mature stand and a mature stand that had already been treated but not eradicated a few years previously could end up taking longer than 34 years to completely kill off. Legislation and compliance UK legislation Despite what many people believe, neither Japanese knotweed nor Giant hogweed are notifiable weeds. Neither plant is cited under any legislation that requires either DEFRA (Department for Environment Food and Rural Affairs) or local planning authorities to be informed of their presence and neither of the plants are listed under The Weeds Act 1959. There are those that believe this is a significant omission in the law. Quite simply, incorrect disposal of knotweed and hogweed material is subject to strong, enforceable legislation in the UK but the natural spread of these plants appears to be relatively immune from prosecution or other legal action. DEFRA themselves concluded in 2003: 'There is no explicit legislative requirement or provision for the control of nonnative species apart from the Destructive Imported Animals Act as it pertains to nonnative mammals and the Environmental Protection Act as it pertains to the control of soil and waste containing Japanese Knotweed... Enforcement of the existing legislation is generally weak'. (Review of nonnative species policy: report of the working group DEFRA, 2003). Their conclusions were supported by English Nature in 2004 but there has been no further movement to improve this situation in the intervening years in regard to natural knotweed or hogweed spread. If a landowner/property owner finds themselves in a dispute with their neighbour over knotweed spreading across the boundary, the best solution is often to try and negotiate a settlement outside of the courts, as current legislation offers little support (see frequently asked questions ). Third party action is usually the only legal alternative and reliance on this as a first resort could result in rather expensive disappointment. The principal current legislation is as follows: Wildlife and Countryside Act 1981 Part I, Section 14, Clause 2 of the Act states: '... if any person plants or otherwise causes to grow in the wild any plant which is included in Part II of Schedule 9, he shall be guilty of an offence.' Page 14.
Schedule 9 has been updated a number of times since the original introduction of the Act, adding various species to the original list, but has always included Giant hogweed and Japanese knotweed. Even though this means a person is bound by law to undertake all reasonable steps to control Japanese knotweed or Giant hogweed growing on, or infringing onto, their land, the terms 'causes to grow' and 'in the wild' have left the wording of the Act ambiguous enough to make it pretty much ineffectual when it comes to legal prosecution. Environmental Protection Act 1990 and Environmental Protection (Duty of Care) Regulations 1991 Section 34(1) of the Environmental Protection Act 1990 imposes a duty of care on any person who imports, produces, carries, keeps, treats or disposes of controlled waste and this includes both Japanese knotweed and Giant hogweed. Section 34(5) subjects all those likely to come into contact with controlled waste to ensure the journey the waste takes from site of origin to site of disposal is fully documented, with all documentation retained and available for inspection if required by the proper authorities. All reasonable care must be taken to ensure no material is accidentally spilled en route. As 'controlled waste', any knotweed or hogweed material (including any soil or building debris containing them) must be disposed of in the UK within set guidelines by prior arrangement at a suitable licensed landfill facility. Penalties for incorrect disposal can include a large fine or even imprisonment for up to two years. Lack of legal case data While prosecutions for incorrect disposal of knotweed material under the Environmental Protection Act 1990 and Environmental Protection (Duty of Care) Regulations 1991 are quite public and relatively easy to locate, finding legal case data for the spread of knotweed across property boundaries probably the most common legal problem relating to the plant is almost impossible to find. The inadequacy of the wording of the Wildlife and Countryside Act 1981 means that all such prosecutions tend to be private third party actions and there is no central register for them. Therefore, unless you already know the details of the court case to look up, you are unlikely to find much legal precedent. Fortunately, a case from 1995 was cited in Child and Wade's The Japanese Knotweed Manual (Packard Publishing, 2000), providing an indication of how things can work out if the claimant proves successful. Annoyed about knotweed spreading into his garden from adjacent councilowned land, Mr Flanagan took his local authority, Wigan Metropolitan Borough Council (WMBC), to court in June 1995 (Leigh County Court, Case Number 93.00392). He won the case and WMBC were required to treat the knotweed along the property boundary with herbicide for three years and install a reinforced concrete barrier to prevent further infestation. They were also liable for costs incurred. While this may make the picture seem quite black and white, the truth is that existing legislation is still vague enough to allow many such actions to fail. Some may fail to even reach court in the first place because the claimant runs out of money beforehand. Even a win can prove expensive in time and legal fees. Further information The knotweed code of practice In 2006, the Environment Agency (EA) released an official code of practice relating to the treatment of Japanese knotweed. Aimed particularly at knotweed occurring on sites scheduled for development, the code is titled: Managing Japanese knotweed on development sites: the knotweed code of practice. It contains a great deal of useful information, including: Page 15.
the role of the Environment Agency in the treatment and disposal of knotweed; legislation relating to knotweed and its treatment; the range of treatment options available; how to identify knotweed; and plants often mistaken for knotweed. It also contains information on knotweed management plans, which the EA strongly advise implementing on development sites, and includes a template for drawing up such a plan. The code is available to download free from the Environment Agency website. Websites Department for Environment Food and Rural affairs (DEFRA) Environment Agency The Japanese Knotweed Alliance Page 16.