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Killing Japanese knotweed

alex69chargeralex69charger Posts: 15
in Problem solving
Moved house last year & discovered JKW at the end of the garden 100ft from house, I had it sprayed in May & Sept with asteroid biocare glyposate concentraite diluted at 50:1 ratio by a landscape gardener I know, he said this would eventually kill it. So far so good there is no new growth this year but what really confuses & frustrates me is assuming it eventually does die, what do I do then ?. I've an area approx 4-5 sq meters fenced off from the rest of the garden as if it was chernobyl & I can't find out what to do, I've contacted companies who all want me to employ them at approx 3k for spraying it with exactly the same stuff, i asked if they would eventually dig it up & they said no, well how does this help ? As far as i'm concerned the thing would still be in the ground, will it, crown roots & all eventually rot as last years dead is still protruding above the ground or should a certain section of the crown be removed ?



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  • wild edgeswild edges Posts: 9,926
    If the JKW just in one place or has it crept in from elsewhere? If it's also outside your boundary then it will be a repeat problem unless it is dealt with wherever else it is growing.

    It might be worth contacting your local council and see if they have their own treatment and monitoring scheme. The council here do and it works out cheaper than using specialists.


    Tradition is just peer pressure from dead people
  • glasgowdanglasgowdan Posts: 632
    Just remove the fence and enjoy the garden! If it appears in future, spray it again. Treat it like any other garden weed, although a bit more urgently once it appears, and don't put it in the compost or council collection bins!
  • pansyfacepansyface Posts: 22,318
    https://www.gov.uk/guidance/prevent-japanese-knotweed-from-spreading
    All the official things you need to know.
    Apophthegm -  a big word for a small thought.
    If you live in Derbyshire, as I do.
  • alex69chargeralex69charger Posts: 15
    As a precaution both sides of the boundry were treated, I contacted the council as I know some do help with dealing with but unfortunately ours don't. There just doesn't seem to be any definitive answer of what to do after it's been treated, I'm told after 2 yrs of recurring growth it's classed as dead but that's as far as the information goes which is absurd.
  • pansyfacepansyface Posts: 22,318
    The link above would suggest three years.
    And here is something else to bear in mind:
    https://tpknotweed.com/removal/residential/japanese-knotweed-mortgage/
    Apophthegm -  a big word for a small thought.
    If you live in Derbyshire, as I do.
  • wild edgeswild edges Posts: 9,926
    Swansea university are doing ongoing trials that found that nothing kills JKW for at least 3 years of treatment.

    http://www.bbc.co.uk/news/uk-wales-south-west-wales-43882916

    Just checked a knotweed management plan that we've been provided with for a project I'm working on: "All plant stems, crowns and rhizomes must be allowed to decompose on site or removed to a licenced location". "During the winter dead canes can be cut at least 15cm from the ground , left to dry out on a protected surface and burnt."

    The disclaimers read "herbicide applications alone can ultimately render the plant unable to produce new growth (deemed as eradication) but are unlikley to remove viability from 100% of the underground rhizome system)"

    The program we're working to is a 3 year spray, 2 year monitor with a 10 year guarantee.
    Tradition is just peer pressure from dead people
  • alex69chargeralex69charger Posts: 15
    Wild edges, i read about the Swansea trials, so the dead can be cut no less than 15cm above the ground ie 10 cm is too short, is this correct ?
  • wild edgeswild edges Posts: 9,926
    That seems to be the case. I assume the canes cannot be guaranteed to be dead below that point but I will ask the contractor to clarify that as I'm curious too. The scheme requires a 7 metre control zone around the knotweed in all directions from the furthest point of the above ground growth. It was sprayed last year and is showing strong growth already this year.
    Tradition is just peer pressure from dead people
  • [Deleted User][Deleted User] Posts: 0
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  • wild edgeswild edges Posts: 9,926
    Freddies Dad said:
    Japanese knotweed has been growing in the U.K. since 1850. Why is it that suddenly it is a problem when for 150 years there are no reports of it rampaging or causing issue?

    I firmly believe that trying to kill it is the worst thing to do. The plants survival mechanisms set in and it grows rapidly in response to attacks. 
    Because mortgage companies refuse to cover houses where JKW is growing anywhere nearby.

    You're talking about a plant that grows happily on the side of volcanoes. It can get buried under metres of molten lava and still grow back by busting through the rock when it's hardened. That's some impressive survival mechanisms.
    Tradition is just peer pressure from dead people
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