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How to kill Japanese Knotweed | How to Control and Treat Japanese Knotweed

Japanese Knotweed. Fallopia japonica var. japonica - Killing this invasive weed

Japanese Knotweed has been around for years. Many many years, for as a young boy, I used to use the hollow stalks for peashooters. My friends also used to 'smoke' the dead stalks in the winter, but that is another story!

Nowadays - some 55 years on - it has become public enemy number one insofar as weeds are concerned - it is not easy to kill or control! No longer a toy, but now a serious menace - so much so that there are strict rules (laws) governing what you can and cannot do if you have the wretched weed!

Japanese Knotweed treatment is essential as it can cost building contractors and developers dearly - sometimes many thousands of pounds if they have it on their building site. Control of Japanese Knotweed is essential.

Furthermore, if soil removed from a building site is proven to have any trace of Japanese Knotweed, then there are hefty fines that can be imposed, together with which there can by claims for compensation if the recipient's land becomes contaminated with Japanese Knotweed. You need to know how to kill and then controlJapanese Knotweed.

Killing Japanese Knotweed

Japanese Knotweed at its worse!

It is an invasive weed - spreading relentlessly through the UK after being introduced by some unsuspecting plant hunter as a highly desirable exotic garden plant in the middle of the nineteenth century. It does not spread by seed, for it is infertile. So all of the weed crops are seen throughout the UK were spread vegetively. They started their new life as a little bit of plant - maybe just a centimetre long that was transported to the new home! This can happen by way of topsoil import, being carried by birds or animals, or even by some unsuspecting and untidy human.

Certainly the transportation of building site excavation material and debris has been a contributory factor in the spread of Japanese Knotweed - as has the moving of general garden waste and rubbish from an infected area to a landfill site and thereafter to anywhere! Waterways, railway embankments, roadside verges, building sites, and of course, gardens, are all potential home to the Japanese Knotweed (- Fallopia japonica var. japonica).

In the native habitat, Japanese Knotweed has several 'predators' ranging from certain insects and a few diseases. These keep the 'problem' confined. In the UK, no such predators exist - though experiments suggest that a small insect can now be released, which will feed on the invasive weed, and hopefully control its spread if not in time totally eradicate it. Hopefully this insect will not then turn its attention to our ornamental varieties of Knotweeds - Persicarias and Polygonum!

As a garden weed, it can cause many problems in borders, or invade lawns - where the small fragments cut up by a lawn mower can then spread to other parts of the garden. These lawn mowing can also then be transported to other areas by way of household waste, or by fly-tipping garden maintenance operatives. Not all garden maintenance firms are fly-tippers of course!

Structural Damage caused by Japanese Knotweed

As well as being a 'weed' Japanese Knotweed is a serious problem in terms of structural damage. Once it has taken hold in ground near to buildings, it can soon cause problems of damage to buildings and certainly paved areas such as footpaths and patios. The underground stems (Rhizomes) are capable of diving down into the soil to a depth of 3 metres. Japanese Knotweed has even been found to be growing through the floorboards of a living room, after presumable growing under the foundations of the house! So - NOT to be ignored. One it takes hold, it is capable of spreading over an area of a few hundred metres within the space of a year!

Control and Treatment

If you find Japanese Knotweed (Fallopia japonica var japonica) on your land, it is your responsibility to eradicate it - kill it - control it,and prevent its further spread. It is no use just phoning the local council. It is your problem. You are responsible foryour own Japanese Knotweed Control. If of course, it has been bought on to your land with a load of topsoil, or other similar provable source, then you have a claim against the persons who imported it onto your land. If you are in a new build property, and suffer from the weed, then it may well be that there is a case against your builder!
Don't try composting it, this will not kill or controlit - it is a waste of time and will lead to problems if you then use that compost on your garden!

Weedkillers and how to Kill Japanese Knotweed

No weedkillers which are persistent in the ground should be used for controlling, treatment or killing Japanese Knotweed (Fallopia japonica var japonica). The two Japanese Knotweed Treatments which seem to offer the best solution in the UK are those with Glyphosate as main treatment ingredient, or weedkillers containing 2,4-D. Glyphosate is normally sold under the brand name of Roundup, Tumbleweed or Elimin8. There are others!

If you mean business with getting rid of Japanese Knotweed, then you should invest in a good sprayer and use the concentrate form of the weedkillers, rather than the silly little Ready to Use spray cartons.

Glyphosate and 2,4-D can be used as a Japanese Knotweed Treatment foliar spray - READ THE DIRECTIONS!. It will need to be applied over 2-3 years to totally kill off the Knotweed. This is a long term war, and for success you will need to win several battles!

A further method that can be adopted - though rather time consuming - is that of 'injecting' the stems with a strong solution made from the concentrate. In this case, it will need to be around plusten times the recommended dilution used for spraying. It has been said that the best time for 'injection, is during the Autumn months. We disagree with this, and have seen this carried out very successfully in the full growing season. The mixture can be directed directly into the hollows stems, but far better to cut the cane stems to around 8-10in from the ground - just below a visible joint. This will give you a hollow receptacle into which you can pour approximately your mixture - about 2-3 cm deep.

Any further re-growth - and there will be some, can then be foliar sprayed in the normal manner.

Remember, both Glyphosate and 2,3-D are weedkillers that will also kill off any of your prized plants if you accidentally spray them. The same is true of your lawn!

Alternatively, you can enlist the help of a professional weed clearance company.

Recommendations for for control of Japanese Knotweed for contractors and building development

The costs - direct and indirect - can be quite considerable if found on building land. Directly, you can negotiate a better price or price adjustment to take into account the expense of dealing with Japanese Knotweed. You cannot simply ignore it, as a buyer or a seller. By law, Japanese Knotweed has to be dealt with. Early identification of Japanese Knotweed is essential in obtaining land for development purposes, or land that has laid vacant and is now being considered for development.

Soil which has been contaminated with Japanese Knotweed will need to be treated before it can be re used on the site for landscape or other purposes. The alternative being that untreated soil will need to go to landfill - at cost. It is essential that your staff can identify Japanese Knotweed or a consultant employed to advise. Likewise, no topsoil should be allowed on to your site until there has been an inspection of the load, and it is assessed as being free form the weed.

A suitable member of staff should be delegated to ensure that all of this is in place. It is an offence under the Wildlife and Countryside act 1981 to allow Japanese Knotweed to be spread into the wild. Together with this, all waste containing Japanese Knotweed is subject to control under the Environmental Protection Act 1990. Developers and contractors may get advice on the Environmental hotline - 08708 506 506.


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