How to kill Japanese Knotweed.
Fallopia japonica var japonica control
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!. 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! It can
cost building contractors and developers dearly - sometimes many
thousands of pounds if they have it on their building site.
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 Japanese Knotweed
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 Polygonums!
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 - and
prevent its further spread. It is no use just phoning the local
council. It is your problem. You have to kill your own Japanese
Knotweed. 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 it - it is a waste of
time and will lead to problems if you then use that compost on your
Weedkillers and how to Kill Japanese Knotweed
No weedkillers which are persistent in the ground should be used for
controlling or killing Japanese Knotweed (Fallopia japonica var
japonica). The two which seem to offer the best solution in the UK
are those with Glyphosate as main ingredient, or weedkillers
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
Glyphosate and 2,4-D can be used as a 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 ten 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 canh 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
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.
Further information on codes of practice etc can be obtained via