What is Japanese Knotweed? and Why is it a problem?

of the dock family

• can grow as much as 2 cms per day
•  3 metres by June
•  root as small as 0.8 grams can grow
•  can extend several metres around and beneath
•  3 year treatment plan approx cost for small sq metre area £1500 - £2500

Japanese Knotweed

What is Japanese Knotweed?

What is Japanese Knotweed? Japanese Knotweed was introduced to the UK as an ornamental plant during the 1800s. It is commonly found today along railway lines, riverbanks, roads and footpaths, in graveyards, on derelict sites or anywhere that it has been dumped, dropped or deposited.

What does it look like?

Japanese Knotweed, identified as a Bamboo like plant, grows with enough force that it can through penetrate concrete other solid foundation structure, therefore posing a risk to the structural integrity of the buildings themselves.

Japanese Knotweed forms dense clumps up to 3 metres in height. It has large, oval green leaves and a stem that is hollow and similar to bamboo. Usually in early spring (although it can be later in the year) the plant produces fleshy red tinged shoots. These can reach a height of 1.5 metres by May and 3 metres by June.

This plant can grow as much as 2 cms per day and will grow in any type of soil, no matter how poor. Towards the end of August clusters of cream flowers develop and then produce seeds that are sterile. The plant dies back between September and November.

Beneath the position of any stand of Japanese Knotweed will exist an extensive underground root (rhizome) network that can extend several metres around and beneath depending on ground conditions. Japanese Knotweed does not produce viable seeds in the UK. The spread of the plant is vegetative, i.e. all new plants are created by fragments of existing plants. A fragment of root as small as 0.8 grams can grow to form a new plant. It is widely assumed that that there is only one species of Japanese Knotweed. In fact there are three species to be found within the United Kingdom which are:

• Fallopia Japonica (common Japanese Knotweed)
• Fallopia x Bohemica (hybrid between Fallopia Japonica and Fallopia Sachalinensis)
• Fallopia Sachalinensis (Giant Knotweed)

Why is it a problem?

Japanese Knotweed grows pretty much anywhere, from field edges to sand dunes, through tarmac and out of lampposts. The speed with which it has spread to all parts of the UK has been spectacular when you consider that it does not leave seeds behind but grows from pieces of the plant or root system that is cut and transported by people or by water.

Because Japanese Knotweed does not originate in the UK, it does not compete fairly with our native species and is able to spread unchecked. Once established, Japanese Knotweed shades out native plants by producing a dense canopy of leaves early in the growing season. Although Japanese Knotweed is not toxic to humans, animals or other plants, it offers a poor habitat for native insects, birds and mammals.

Japanese Knotweed is an asexual plant and can only reproduce by its own plant tissue, be it roots or stem nodes. In late summer flowering takes place but these flowers are sterile and incapable of producing further plants. Its roots, known as rhizomes, spread outwards beneath the soil surface. Growth is rapid, Japanese Knotweed can be as tall as 3 – 4 metres by the end of the autumn. It is important to remember that a mature Japanese Knotweed plant has at any given time, a root system that has spread up to 7 metres in all directions.

Because Japanese Knotweed can only spread by its own plant tissue, it is mainly the activities of man which has ensured the spread of this invasive weed. Removing any plant debris and dumping it elsewhere will ensure that fresh colonies become established. Strimming of stem growth will additionally spread plant material which will be prone to re-establishment. The flow of water in rivers and streams is the only other way that nature has of spreading plant material. The action of moving water adjacent to river banks breaks off small parts of Japanese Knotweed which then spread downstream to make fresh colonies elsewhere.

Knotweed instinctively searches sources of water damaging further any existing gaps and cracks in and around the affected areas. Although the scale of damage may vary from those who are judging damage will generally run in the form of:

Sewers, Drains and Down pipes

Crack and gaps within pipes will be further widend and damaged by Knotweed. The persistent build up of the roots will lead to the slowdown and eventual blockage of the drain run itself requiring in the worst form the renewal of the affected drains.

Patios, Paths and Driveways

Surfacing Knotweed will see the bulbs penetrating through paving Patio slabs and joints, tarmac and through brick paving.

Boundary and Retaining walls

Tightly pack clumps of Knotweed can lead to the undermining of the garden walls' shallow foundations leading to the eventual destabilisation and possible collapse of the wall itself.

Outbuildings and Conservatories

Knotweed can overwhelm destabilization smaller outer buildings that have light, poorly built or freestanding foundations (sheds). Like garden walls this can lead to the sudden and part collapse of the structures themselves. Valuers however will attribute greater importance should a conservatory be affected due to the close proximity to the main buildings foundations.

What are the environmental issues associated with Japanese Knotweed?

Under the Wildlife and Countryside Act 1981 / Wildlife (Northern Ireland) Order 1985 it is an offence "to plant or otherwise encourage" the growth of Japanese Knotweed. This could include cutting the plant or roots and disturbing surrounding soil if not correctly managed.

Any Japanese Knotweed polluted soil or plant material that you discard, intend to discard or are required to discard is classed as 'controlled waste' and should be disposed of in accordance with the Environmental Protection (Duty of Care) Regulations 1991.

Japanese Knotweed should be disposed of in a licensed, lined landfill site. Be sure that you notify your waste haulier that the waste to be removed contains Japanese Knotweed. You should also contact the landfill site several days before any material containing Japanese Knotweed is taken there to allow a suitable area to be prepared for its disposal.

Control of Japanese Knotweed

Although there are a number of options available for the treatment of Japanese Knotweed, the majority of these require a number of years in order to be effective. The two methods outlined below are the most effective in the time scales generally required by the construction industry.

Japanese Knotweed Risk Category

Category 4 - Knotweed is causing serious damage to or is in 7 meters of habitable space, conservatory, garage or outer buildings- Requires further information by an appropriately qualified person.

Category 3 - Japanese Knotweed is present within boundary of the property but is 7 meters outside of any habitable space, conservatory, garage or outer buildings.

Category 2 - Japanese Knotweed was not seen within the boundaries of the property but was seen in a neighboring property within 7 meters of habitable space, conservatory, garage or outer buildings.

Category 1 - Japanese Knotweed was not seen on the property but is evident on neighbouring land outside of 7 meters of habitable space, conservatory, garage or outer buildings.

Eradication Methods

1. Spraying with Herbicide

   Spraying the plant with an appropriate herbicide is the most effective option available, however it can take several years and rarely achieves eradication without mechanical disturbance. Herbicide treatment can give the appearance of control but the rhizome network (roots below ground) may still be viable and disturbing the ground will cause the plant to regrow. Soil movement should not be attempted until no rhizome remains in a viable condition.
   Spraying can only be carried out during the growing season when there is green, leafy material present. Herbicide treatments take effect within a few weeks but eradication can take a minimum of two sprays in one growing season to achieve. Often, when a contractor takes control of a site, the working programme is tight and does not allow sufficient time for this method of eradication to be used. Even so, a spraying programme may be an option for weakening the plant before removal or treating regrowth and remaining plants in the spring.
   Anyone planning to spray a herbicide must be "competent in their duties and have received adequate instruction and guidance in the safe, efficient and humane use of pesticides." This means that the person who will be undertaking the spraying must hold a Certificate of Competence for herbicide use or should work under the direct supervision of a certificate holder. A Certificate of Technical Competence can be obtained by attending a short course at an agricultural college or similar institution.
   The most effective active ingredient for use on Japanese Knotweed is called Glyphosate. This is the active ingredient found in 'Round Up' and other similar herbicides. It is effective on Japanese Knotweed because it does not kill the plant immediately. Instead, the herbicide soaks through the leaves and is taken into the plant root system. The greater the number of green leaves present, the larger the quantity of herbicide that can be absorbed into the plant. It can take up to ten days for the plant to begin to die off after treatment and you should always watch for regrowth.

2. Digging and Spraying

   A quicker method of removing Japanese Knotweed involves the clearing of above ground leaf/stem material and the removal of ground material polluted with roots. Care should be taken to ensure that all Japanese Knotweed roots are removed - this is one situation where it pays to remove too much material.
   Even with great care, a certain amount of regrowth in the spring would be expected and any should be treated with an appropriate herbicide as discussed above. Make sure you read on for tips on how to prevent spreading Knotweed fragments around the site during the works.

   Excavation of the plant and its roots

   As Knotweed and the soil in which it lay is considered contaminated it must be excavated and disposed off by a license waste control facility. The scale of excavation will depend on the infestation but you can expect soil to be excavated up to 3meters vertically and 7 meters horizontally from the top soil layer. In December 2011 disposal prices ranged from £25 to £50 per tonne. Typically off site disposal will cost up to several thousand pounds

   On-site burial and encapsulation with membranes

   The Knotweed itself may be excavated and reburied on site with overburden (a specialist Knotweed resistant membrane) to a depth of no less than 5 meters below top soil. To prevent any re-growth the overburden layer must be encapsulated with a Knotweed resistant barrier encapsulating the affected area.

   Biological treatment

   The introduction of a pest which attacks Knotweed is known as a Biological Treatment. This approach not eradicates the Knotweed entirely but will instead keep it at a controllable level.

3. Disposal of Japanese Knotweed Polluted Material - Removal from Site

   • Polluted material should be removed from the site for disposal, unless otherwise agreed with the Environmental Regulator and Client.
   • As Japanese Knotweed is considered to be a pollutant, you can apply to Customs and Excise for a 'Landfill Tax Exemption' for polluted soil. For further information on the Landfill Tax and exemptions, use the links to LFT1 and LFT2 in the 'See Also' box.
   • Any bags/skips containing Japanese Knotweed or polluted soil leaving the site should be covered to avoid spread along public highways.
   • Waste Transfer documentation will be required for any polluted material leaving the site.
   • Check with the disposal site in advance that they can receive material containing Japanese Knotweed. Be aware, the disposal site may require notice to allow an area to be prepared for this material away from the landfill liner.

Best practice, Contractors working near Japanese Knotweed

• Knotweed polluted areas should be clearly marked out on site. Areas that do not need to be disturbed during the works should be fenced off, allowing a buffer of at least four metres to allow for the likely extent of the roots.
• Use of tracked machinery should be limited until areas polluted with Japanese Knotweed have been cleared and/or identified and cordoned off.
• If tracked machinery must be used in areas where Japanese Knotweed is known to be present, then consider using a strong geotextile overlain with hardcore as a base for vehicles to travel on.
• Areas where Japanese Knotweed has been identified should be cleared slowly, one at a time with ongoing assessment of the extent of polluted ground. Only essential vehicles should be present in areas polluted with Japanese Knotweed.
• Never stockpile potentially polluted material within 10 metres of a watercourse.
• On leaving areas of the site known to contain Japanese Knotweed, any tracked machinery that has been used should be thoroughly cleaned within a designated area. This area should be as close as possible to the polluted area on which the machinery has been working to avoid the spread of the species. This area should be monitored in the spring for Knotweed growth and a spraying programme implemented if necessary. Any machinery used in clearing polluted areas should be similarly cleaned.
• Care should be taken to ensure that polluted material is not dropped or transferred to other areas of the site.
• Japanese Knotweed polluted spoil should only be placed on top of a fabric/membrane in an approved, fenced area. Once the polluted material is removed from these areas, it should be monitored for regrowth, particularly during the growing season and, if necessary, treated with an appropriate herbicide as discussed above.
• All site operatives should be made aware of the requirements associated with the removal/disposal of this species in order to help limit accidental spread.
• All haulage lorries or dumpers carrying Japanese Knotweed polluted material should be covered.
• Never use a strimmer, mower (without collection bucket) or chipper on Japanese Knotweed material.
• If you are working between November and March in an area where Japanese Knotweed is known to be present, then dead shoots from the previous year can be a good indication of its location. Even if there is no growth evident above ground, the below-ground parts of the plant will still be alive. Breaking up this root network and transporting either off site or around your site on vehicle tracks will spread the plant. Use the precautions outlined above to reduce the risk of spreading the plant.

How Japanese Knotweed affects Property

• Annual site visit for up to 5 years or more,
• Includes completion of certificate and herbicide treatment if required,
• The fee for visit and treatment is fixed in advance,
• May be presented to banks, building societies and Local Authorities for consideration in planning and mortgage applications.

Lenders are cautious to loan on properties affected by Knotweed. Although cases are reviewed on a case by case basis lenders will generally not consider loans unless either an initial treatment program has implemented or there is a commitment from the owner(s) to fund an advance treatment program lasting (typically between three to four years).

Some of the following firms in the link below may be useful
http://www.japaneseknotweedcontractors.co.uk/

BUT

Each bank or mortgage lender is likely to have different preferred contractors. A spokesman from Santander said: “If the weed threatens the structure of a building, then a mortgage application would be refused.” Rival lender Nationwide also admitted that it had turned down mortgages in the past because of Japanese knotweed growing close by houses.

“There have been cases when we have been prepared to lend on a property with knotweed and cases where we haven’t been prepared to lend. It depends on the proximity of the weed to the property and the commitment of the relevant parties to eradicating it,” said a spokesman for Nationwide.

Controlling the invasive weed is costing homeowners thousands of pounds as professional eradication of the weed comes with a hefty price tag. Eradication programmes can cost up to £5,000 over several growing seasons.

The example below describes the consequences of when Japanese Knotweed is left untreated:

"The price of a couple's Hertfordshire house has dropped by more than £250,000 because Japanese Knotweed has invaded it, according to an independent surveyor. With its value falling from an estimated £305,000 to £50,000, experts have told owners Matthew Jones and Sue Banks from Broxbourne that, unless action is taken, it will be impossible to sell. They have been told 10 feet of soil needs to be removed from beneath the foundations to remove the plant. The invasive weed was discovered in the garden of their new-build house in April 2009 after they had been living there for about a month. A couple of months later it was found growing in the dining room. ..Just two months later it was found underneath breaking through the skirting boards and displacing floor boards"

What to do

• Ensure that any contractor is acceptable to a range of mortgage lenders or banks by asking for their track record and references.
• Let occupiers of property know that the plant is present and may restrict lending.
• Ask them to confirm that any contractor suggested by us is acceptable to their lenders.
• Let them know that any work has to be guaranteed for five years and subject to a long term insurance backed guarantee by a company already accepted by mortgage lenders
• Check that any company is what they seem to be there are many rogue firms about.
• Do not let ordinary gardeners or clients remove the plant themselves this will only make matters worse.

Companies that deal with knotweed are:

TP Knotweed Solutions

- 3 year treatment plan approx cost for small sq metre area £1500 - £2500
- 5 year guarantee after treatment period
- 2 year treatment per year winter clearance & 3rd year clearance

JapaneseKnotweed LimitedEnvironet UK