Japanese Knotweed: The Silent Nuisance

Mike Hedges looks at the damage caused across Wales by Japanese Knotweed.

Japanese knotweed is the cause of a great deal of anguish and despair in Swansea. Known locally as “Sally Rhubarb” due to its similarity in shape and colour to rhubarb, experts estimate that the Swansea area alone has around 62,000 tonnes of the stuff, which is the equivalent weight of 400 blue whales.


The truth however is that Japanese Knotweed is one of the most damaging non-British species of weeds we have in the UK. Fallopia Japonica, to use its scientific name, was first introduced around South Wales in the 1800s by wealthy Victorian families in the belief that it was an ornamental plant.

Japanese knotweed can grow at an astonishing speed and with the power to push through concrete and tarmac, damaging buildings, roads and pavements in the process.

As the plant has no natural domestic predators, it can both damage and out-compete our indigenous species at an alarming rate, with the tiniest piece of stem being able to re-grow into a fully-fledged nine foot giant. We’ve seen this pest take over gardens and land throughout Britain with only the Orkneys being clear of it.

The horrors associated with Japanese Knotweed are not just limited to the environment. In recent years, we’ve seen knotweed affect the housing market, with many mortgage lenders now refusing to give financial backing to buy a property where the weed is present, and in some cases, when it is present on a neighbouring property or neighbouring land. This effect has seen the value of knotweed-riddled properties and those in knotweed infected areas drop, with frustrated homeowners left having to spend thousands of pounds to clear it before they are able to sell their house.

It’s therefore unsurprising to learn that each year, Japanese Knotweed is seeing landowners and public authorities spend an estimated £150m to control and clear-up the pest, which is also costing the British economy an estimated £165m annually, whilst estimates put the total cost to clear the knotweed infestation at around £1.5billion. The problem for homeowners doesn’t stop there; the removal of knotweed is both expensive and difficult to eradicate because as all the roots need to be completely removed to prevent any future resurgence.  One small part of a root left behind and a new plant will grow and prosper.

So what weapons do we have in the armoury to combat the invader?

Physical control and chemical methods are the two main types of treatment; however, in the quest to find an answer, an innovative trial has already begun into using a “natural control” as a feasible and long-term solution to controlling the weed.   Up until now chemical treatment has been both expensive and lengthy, with treatment having to be carried out over at least three years but Swansea University is working on a new chemical means of destroying knotweed.

In July 2009, DEFRA announced plans to release a native sap-sucking psyllid bug, known as the Aphalara Itadori, into the wild to help control knotweed. The psyllid bug, which is the first time a biological method has been used in the EU as a natural control of a weed, was released on several test sites in spring 2011 under the control of the Centre for Agricultural Bioscience International.

The project is currently in its fourth year of five, and according to a recent update from the then Natural Resources Minister Alun Davies, “early signs are encouraging” and the bugs are coping well in the UK. However, as the Minister acknowledged, natural control is not a “quick fix” and successful bio-control methods usually take around five to ten years from release before the overall benefits can be realised.

Let’s hope that this natural control project gives us the “silver bullet” needed to tackle the knotweed once and for all, not least because so many hopes are resting upon the small shoulders of these bugs!

Mike Hedges is the Assembly Member for Swansea East.

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