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Japanese Knotweed

Last post 01-12-2005 11:16 AM by ndhort. 9 replies.

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  • 18/10/2005 08:57 AM
    • jingles56
    • 18 Oct 2005
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    We recently moved house and were less than delighted to find the end of the garden (30'' by 15'' area) infested with this little darling. I have dug up a lot of the rhizomes and sprayed with roundup and this seems to have had little impact. There is also the problem that the spread of rhizomes goes into adjoining land which is owned by a block of flats and we doubt that they will be active in its eradication. I have decided to get heavy on this weed and am digging down 3 feet wherever it grows and am pulling out all the rhozome material I find. I have been told that if I place a barrier material down and then cover this with soil (which I will seive for rhizomes) this should prevent further growth from anything I have missed that is deeper. The question is, what barrier material would you recommend and also is there any vertical barrier I could put up along the boundary of our property to prevent re-invasion from next door (we are unsure where the plant originated, on their land or ours). I had thought of putting down aluminium sheets do a depth of three feet but did not know if this would contaminate the soil with metals after time? Any advice would be appreciated.

  • 19/10/2005 12:30 PM
    • Obelix
    • Belgium
    • 24 Nov 2004
    • 442
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    I had understood that Japanese knotweed is a notifiable weed so if you inform your local council, they will either do something or oblige the flat owners to deal with it. I disposed of horsetail by regular spraying and "stroking" with triple strenght glyphosate solutions. It took a while but worked in the end. You could try the same with your knotweed and leave a strip of land at the bottom of the garden for it to grow into and be sprayed in. You could disguise the strip with a row of trellis and climbers. Can't help with the aluminium sheets but maybe a sheet of rigid plastic in front would protect you from any bad stuff if it starts to break down.

    Obelix - Belgium
  • 19/10/2005 12:40 PM
    • William
    • 24 Nov 2004
    • 210
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    Since it grows deeper than 3 ft and even can penetrate macadam maybe better have a look at this website http://www.ex.ac.uk/knotweed/ PS it can go down at least 3 metre and the rhizome can spread 7 mtr form it home base.....

    Happy Gardening, William
    (Netherlands)
  • 19/10/2005 03:03 PM
    • jenni
    • 20 Jul 2005
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    Having read your post earlier, I was surprised to see just now on my return from a walk a small van advertising a company specialising in Japanese Knotweed control. I memorised their website (it wasn't difficult!) in case it may be of any use to you: http://www.japaneseknotweed.co.uk/ You may find some useful information on it. Their root barrier section indicates a barrier of not less than 2 metres is required! Good luck.

    Jenni
  • 20/10/2005 08:28 AM
    • jingles56
    • 18 Oct 2005
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    Thanks for the suggestions everyone. I had actually spotted that site Jenni, but thanks anyway for putting it up. I do love the picture of the person installing the vertical root barrier and reading the note that says it has to be installed to a minimum of 2m... while the picture patently shows about three feet of soil depth.

  • 21/11/2005 06:27 PM
    • ipt8
    • 22 Nov 2004
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    Keep spraying with Roundup. Buy your Roundup from an agricultural supplier, I have a feeling it is a stronger solution than that at garden centres. If I remember correctly a litre costs up to £20 and I used it at the recomended strength for tree stump control. Bruise it and spray it.

    I P Terry
  • 24/11/2005 10:48 AM
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    Fallopia Japonica or Japanese Knotweed has been an introduced species since about 1890 and has became a real pest. The weed is not specifically covered in the wildlife and countryside act, rather bundled in with two other problem plants. While it is an offence to plant it, it is not an offence to ignore it. In fact if you do attempt to dig it out, beware as there is specific legislation relating to its disposal and must be disposed of on a registered landfill site as a dangerous or obnoxious substance. The landfill operators must be informed and they must follow specific rules on its disposal. It takes only a small piece of root to create a new plant, it also seeds profusely. I approached the Government in 2002 after I got nowhere with my Council, I was informed that it would be looked at in 2004/5 under the new Biodiversity Panel, created to look at items such as this. I also petitioned the European Union (Petition 239/202) declared admissible on 25th September 2002 under rule 175(3) It has taken since that date to get a reply, of which I received just two days ago. They of course recognise the seriousness of the problem and will be advising its members. So that is about the strength of it. I would suggest anyone who does have a problem, to contact their Member of Parliament and ask them to do as I did and demand change to legislation, a simple alteration to the Weeds Act to include non native species would force Councils to resolve the matter. Why can we not have rules such a in New Zealand where it is not only against the law to plant non native species, but an obligation to remove them with hefty penalties for those who ignore the Law with an environmental police to back it up.

    Terry Harding
  • 24/11/2005 11:16 AM
    • miranda
    • Oxfordshire
    • 17 Nov 2004
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    Jingles, I think glyphosphate is a systemic herbicide and works best on actively growing plants, which take it in through the leaves. You'd be better to wait till the plants start growing again next year, when you can give the whole plant a good drenching. Using it now won't have much affect.

  • 30/11/2005 03:24 PM
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    There is a product called Rootbarrier (previously called Rootcontrol), manufactured by Dupont and available from the company Green-tech Ltd - www.green-tech.co.uk To view it on their website, go to 'site map' and you'll find Rootcontrol under the heading 'Trees'. Regards, Helen, Advisory (RHS)

    Helen Bostock
  • 01/12/2005 11:16 AM
    • ndhort
    • 06 Aug 2004
    • 37
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    I'm confused as to how 'rootbarrier' would control Japanese Knotweed. From the picture shown and from experience at how deep JK can grow, you would need a mini digger, a skip to remove the soil and a very costly product that the odds are won't work, or it would be advertised as a JK barrier. The best thing to do is check the DEFRA website for up-to-date news, sooner or later they will hopefully come up with a solution. I found round up worked as the new shoots were coming through but you had to crush the stems to allow the chemical to absorb into the plants, this was recommended to me by a few headgardeners, and it worked. But you do have to go out on a regular basis to keep on top of it.