Knotweed - an enormous problem

Knotweed (usually with the prefix Japanese) is a major problem in the UK with inadequate laws controlling its growth. It was introduced by the Victorians and for much of its time in the UK there has been no natural insect or caterpillar in the UK to control it. In 2010 an experimental introduction of a predatory beetle began.

A landowner must take steps to prevent it spreading to a neighbour's land (including public highways) and must destroy the cut down pieces by burning on site, by chemical reaction or buried in special deep sites. Under the Wildlife and Countryside Act 1981 (Wildlife {Northern Ireland} Act 1985) it is an offence "to plant or otherwise encourage" the growth but as the law stands it is not compulsory to remove existing plots of knotweed. It is illegal to remove it to a public "household refuge" tip, leave it in dustbins or leave it on land in an unauthorised manner. Removal to a licensed "hazard" disposal tip is under conditions where notice has to be given to enable the waste disposal company or council to enable especially deep disposal in containers. There are no public funds available to eradicate it although a group of landowners adjoining a public path or highway could reasonably expect a council or highway authority to share in the cost of removal.

The average depth of knotweed roots is 6 feet, it grows to between 8 and 10 feet in height and in summer can grow at the rate of 4 inches per day.

Knotweed has been known to grow through motorways, concrete car parks, metal road signs, tarmac and decking. In Australia they use a high pressure steamer to boil the roots, constant strimming actually encourages growth and the plant has developed its own skills in that it can lay dormant for a year or so then spring back into life. Burning the stems with pressurised paraffin or butane gas "shocks" the root into creating new growth. Firms and garden centres who sale flame wands to control weeds are laughing all the way to the bank. There are specialist contractors available but because of the expectation of a landowner that he requires "guaranteed" clearance the contractor charges a high (although to the individual operator a realistic fee) as usually the firm is called back within a short time to have a second or third go at reducing it. Some operators offer a 10 year guarantee, it would be useful to learn of any cemetery owner planning to use such a firm so we could monitor and advise of successful eradication.

One big problem is that it chokes culverts, grows right through drains and sewers and it is particularly difficult to control in cemeteries, grows up through graves and can soon make areas inaccessible. Until our National governments seriously address the spread the situation will worsen with global warming. One TV gardening expert was quoting as saying our country landscape in 10 years or so will be acres upon acres of knotweed.

As many cemeteries have wildlife characteristics or adjoin Sites of Special Scientific Interest there is a reluctance to engage in the use of weed killers. The digging out the root is similar to when you weed your garden, the cleared out area soon encourages weeds rather than wild flowers and it would take great skill and heavy cost in man hours to remove every cm of root. Some brands of weedkiller which attacks the root has had reasonable success but it is a very expensive exercise to spray just the leaves of offending knotweed and avoid neighbouring undergrowth or wild flowers etc. The specialist knotweed control firms are facing a growth industry and some councils now employ teams specialising in the control of knotweed. However what is really needed is an incentive scheme to persuade landowners, gardeners, allotment users, local authorities, private and public landlords and cemetery managers to remove and safely dispose of the roots. This in itself is a recipe for fraud or a danger of spreading the offending rhyzones as any subsidy or incentive scheme would need to do spot checks to minimise fraud. Removal to an 'audit control' site must in turn present risks of the rhyzones spreading elsewhere.

The 2012 Olympics in London with massive overspend of the budget is now faced with enormous problem of clearing knotweed from the 10 acres of waste land earmarked for the Games. The Treasury currently allows tax breaks to developers of brown field sites if they first clear any contamination (known as land remediation relief). Consideration is being given as to whether a similar concession could be given for knotweed clearance. The cost of clearing the ground for the Olympic velodrome and for the aquatic centre at Stratford could add £70 million to the projected cost. For each month the project start is delayed the knotweed will spread at an alarming rate. Perhaps this might focus the government's mind to the alarming spread of knotweed (Fallopia Japonica).

In July 2009 it was announced that permission is being sought to introduce to the UK a parasitic beetle which the Enviroment Agency and CABI Biosciences believe will have an effective control of knotweed. The beetle seeks out knotweed to lay its eggs and the larvae suck the sap causing the plant to restrict its growth. The beetle will not eradicate the problem as parasites normally do not kill off the host as it would diminish its own food supply. Experiments so far indicate that the beetle does not choose any other type of vegetation. The introduction began in 2010 and it will be a few years before a noticeable reduction in the host plant but we will report on future results.

In October 2011 it was reported that a family home adjacent to some knotweed infected wasteland where knotweed was growing up through the floor of the house and the suggestion was that the house would have to be demolished.