Does Japanese Knotweed affect the value of your property and jeopardise a straightforward mortgage offer? The short answer seems to be, yes. And yes, the plant has been found in the Dulwich Area.

Extensive coverage has been given to the effects of Japanese Knotweed on house values and mortgage problems by the media including the Telegraph on 10 July 2013, the Guardian on 8 September 2012 and 9 June 2013, and the Daily Mail on line on 20 July 2013. Those articles and other recent publications refer to the tenacious and deleterious aspects of the plant and the negative consequential issues.

What is the problem? Japanese Knotweed ( Fallopia japonica ) is a rampant perennial plant described as the ‘most invasive species of plant in Britain’ by the Environment Agency. It would not be an issue if its strong invasive root system, which can extend 3 metres deep and 7 metres horizontally, did not have the ability to damage drains, concrete foundations and brickwork, while above ground the plant’s strong growth forces its way through tarmac surfaces and paving.

It is these invasive and destructive aspects that mortgage lenders have picked up on. A survey report identifying the plant as being on the property will have a direct effect on a mortgage offer. However, there are moves by the Royal Institution of Chartered Surveyors to have conditions attached to a mortgage for a recognised treatment regime.

There is legislation, regarding Japanese Knotweed, in the Wildlife and Countryside Act 1981, which makes it an offence to, ”plant or otherwise cause to grow in the wild”, while it is not an offence to find the plant growing in your garden. However, by failing to eradicate it or control it from extending into your neighbours’ gardens it would constitute a private nuisance under common law. That neighbour could apply to the courts for an injunction for the nuisance to be stopped, and claim damages against loss of value of the property and the costs of its removal and any remedial building works. Concealing the existence of the plant on a property before a sale could lead to a claim too.

How to deal with the plant? It is not a simple matter of cutting it down or digging it out to remove it. Digging it out is reported as being ineffective as anything left behind will sprout very vigorously. Under the Environmental Protection Act 1990, Japanese Knotweed is classified as a “controlled waste” requiring it to be disposed of by a licensed waste control operator. Just putting into a composter is not right, at all!

And the solution is? The most effective treatment is reported as being with strong herbicides, like Glyphosate, at appropriate times of the year, such as on re-growth. Even with this approach it can take 4 or more years to eradicate the infestation. Specialists may be able to reduce the timescale by using stronger commercial herbicides.

There is research being carried out on biological control of the plant with Japanese fungi and aphids, but this is not currently a viable short-term option for the householder with Japanese Knotweed in their garden, or those adjacent to them.

The growing number of firms that offer expertise in controlling and eradicating this plant, along with other invasive non-native plants like Giant Hogweed and Himalayan Balsam, reflects the size of the problem. To seek a professional solution look for accredited contractors, and if an insurance backed guarantee can be provided.