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The case of the disappearing Knotweed

Japanese Knotweed has again been in the news recently. As usual it is not good news.

Japanese Knotweed has again been in the news recently. As usual it is not good news.

For the benefit of the very few of you who may not know the background, Japanese Knotweed is an invasive plant introduced into the UK. It is very common in many parts of the country, including South Wales. The problem is that when land has Knotweed growing upon it, many potential problems arise.

One of these is that soil removed from the land, perhaps because building work is being carried out, must be treated as controlled waste. This makes building works more expensive than they might otherwise have been. It also places the land owner at risk of legal action by their neighbours if there is any risk of the Knotweed spreading to neighbouring land. Factors such as these combine to make land which has Knotweed growing on it for less attractive to potential purchasers. Some lenders are quite reluctant to agree a mortgage on properties where Knotweed is present. All this can combine to result in a significant reduction in the value of the house or land. That is, of course, bad news for you if you happen to be the owner of said house or land.

An industry has, grown-up specifically aimed at “treating” and/or all “eradicating” Japanese Knotweed. Some of these companies offer 5 or 10 year guarantees against the Knotweed returning. Such guarantees were, until quite recently, comforting for people who had purchased properties relying upon them.

However, recent research by a team at Swansea University has raised serious doubts about the effectiveness of the treatments which are currently commonly used to tackle an infestation of Knotweed. The research paper can be found here.

It seems to suggest that the current “treatment” even when applied correctly over a period of years leads only to the plant becoming effectively dormant, in that the complex root system remains alive but does not give rise to any above ground growth. This can, therefore, presumably, lead to a resurgence in the plant at some point in the future.

It will be interesting to see how the companies specialising in the “eradication” of Japanese Knotweed deal with this research. In particular, will they still be able to offer guarantees that the plant will not return?

If you have bought a property subject to one of these guarantees, it may be useful to consider the wording carefully in case the plant should return and you need to rely upon the guarantee.

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