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Japanese knotweed - some background

Japanese knotweed has become increasingly well known in recent years and is a growing commercial problem because of the challenges it causes in the urban environment. The plant, which is native to eastern Asia, was introduced in the early 19th century to adorn the gardens of Victorian England. As early as the beginning of the 20th century it was widely recognised as an invasive plant/species. Where the plant grows on development sites, it can cause damage to hard structures and surfaces. Developers also often need to tackle the plant in order to avoid contravening the Wildlife and Countryside Act 1981.

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What are the problems caused by Japanese knotweed?

When growing adjacent to built structures such as walls and buildings, Japanese knotweed rhizomes can exploit cracks and weaknesses as the root network expands. As with other plants, the pressure exerted by the expanding fibrous rhizome (or roots) can split structures along weak points and push up through car parks and drives especially where the asphalt has been poorly laid. 

Japanese knotweed rhizomes in their search for moisture can interfere with drainage pipes and other structures, blocking and sometimes lifting the pipework and clogging sumps. Other underground infrastructure may be at risk, such as cabling and water pipes.

In a similar way to other types of building survey, a specialist knotweed surveyor will take will take the risk of damage from Japanese knotweed rhizome into account in their assessment of a property. This is based on criteria advised by the Royal Institution of Chartered Surveyors.

When knotweed causes problems with the buying or selling a property

Very often, the problem of Japanese knotweed is only discovered during the buying or selling of a home. Where Japanese knotweed is considered to pose a risk to the property, it can be controlled by implementing a Japanese knotweed management plan.

In order to meet the requirements of the mortgage lender, the plan and its execution need to be undertaken by a member of a recognised trade association such as the Property Care Association. The mortgage lenders recognise the standards and professionalism of the PCA along with the assurance that comes with their work.

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What does a Japanese Knotweed Management plan consist of?

There are several ways our PCA qualified specialists may manage Japanese Knotweed, ranging from long term management through the use of herbicide sprays to potentially faster, but more disruptive (and generally more expensive) full scale excavations.

For the majority of homeowners though, a control program and subsequent management plan using herbicide spray is the most common and cost effective approach which causes the least disruption.

Depending on your property and circumstances, this may consist of applying herbicide once or twice in the first year and then once each following year until the plant no longer reappears. The property will be monitored for regrowth for the following two years and if still no regrowth, a Completion certificate can be issued. Were it to reappear within those two years, the herbicide treatment would resume and so on.

Am I breaking the law?

If you have Japanese knotweed growing on your property, unless required to do so under a Community Protection Notice (see below), there is no legal requirement to take any action to deal with it. However, you should take measures to control the plant, so as to prevent it spreading outwith your land boundaries (this includes the roots/rhizomes). If you decide to try and dig-up and remove/dispose of the Knotweed, all wastes generated would need to go to a licenced landfill. 
 
To find out more about Japanese knotweed and the law , click on the link below
 
Japanese knotweed legislation 

What if Japanese knotweed affects your neighbours

 A common occurrence is where the Japanese knotweed on your property extends into the next door neighbour’s plot, or your property is free of the weed but it is close to a boundary with adjacent land. A collaborative approach is by far the best way to deal with Japanese knotweed; indeed, in some instances it may have been introduced to or spread along/between a number of properties. 
 
Achieving collaboration in such cases is challenging and you may decide to take expert advice first from a Japanese knotweed specialist. Once agreement has been reached, a plan drawn up and costs agreed, a solicitor can arrange a contract between all parties. 
 

Japanese Knotweed - affecting neighbours - PCA

Some Japanese Knotweed “do’s & dont’s”

  • Do make a start straightaway to deal with Japanese knotweed growing on your property. The longer you leave dealing with it, the more Japanese knotweed there will be to deal with! It can grow quickly and costs will grow as the plant does.

  • Don’t just cut the plant down and try to cover it up. Apart from being highly irresponsible, the problem could come back very quickly. If you have since sold the house there could even be a legal claim against you.

  • Don’t cut down and/or dig up the plant and put it in the local authority compost collection. This would be breaking the law and Japanese knotweed rhizome is not necessarily killed by the composting process, part of which is to break up the material into small fragments, thereby potentially exacerbating the risk of spread.

  • Don’t contact the Environment Agency, SEPA, Natural Resources Wales or the Northern Ireland Environment Agency to provide advice on your specific situation or to recommend a suitable contractor. They are not able to advise on each and every case and are restricted from recommending contractors.

  • Don’t break the law. Remember, if you cause Japanese knotweed to spread ‘to the wild’ you may be guilty of an offence under the Wildlife and Countryside Act, 1981.  Recent high-court judgements have also established a clear precedent for potential claims of ‘nuisance’ (loss of amenity) from neighbours.

Professional help is available

In order to ensure that Japanese knotweed on your land is effectively and completely treated, we do highly recommend you obtain professional advice. This can range from checking that you have correctly identified the plant as Japanese knotweed through to drawing up and implementing a Japanese knotweed management plan.

In order to ensure that the advice you receive is reliable and recognised by mortgage lenders and other relevant agencies, you should contact a company that is a member of the Invasive Weed Control Group of the Property Care Association.

If you are uncertain and simply want some help, most specialist PCA invasive weed members will be happy to offer advice and guidance over the phone and, if you have pictures, will be happy to look at those before confirming if you need to book a survey.  To find a registered PCA specialist near you, simply use the search tool below. 

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More about Invasive Plants & Weeds

To find more about other invasive plants and weeds, visit our main Invasive Weeds section.

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Amenity Standard Protection

The'assured standard' for weed management practices that ALL PCA invasive weed members adhere to.

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