Japanese Knotweed Killer

Discussion in 'Organic Lawn Care' started by metro36, May 4, 2012.

  1. metro36

    metro36 LawnSite Silver Member
    Posts: 2,412

    I have a customer who has a serious problem with Japanese knotweed. It is rapidly taking over her entire yard. Does anyone have any experience with an organic herbicide that will kill it? I understand that it will kill the plants in the area but the customer says she can live with that. My spray guy can handle it chemically but the customer likes to keep everything organic as she has a couple dogs.

    Any advice would be appreciated.
     
  2. RigglePLC

    RigglePLC LawnSite Fanatic
    Posts: 11,938

    Simple. Just keep mowing it. 5 inches tall. And then shorten it to 2 inches. It does not withstand mowing...eventually. When the top cannot use photosynthesis to send needed food the roots, the roots die. You may wish to reinforce this by digging out most of the roots with a forked implement, like a Dingo or front loader. Use pruning shears or string trimmers to cut off any sprouts that escape--never let any sprout get over 6 inches tall.

    Of course, you may need to wait until winter when frost kills the tops, but not the roots. Cut it down, then...get ready to mow in spring. Use your oldest blades at first.
     
  3. metro36

    metro36 LawnSite Silver Member
    Posts: 2,412

    Thanks for the reply.

    Its mostly growing in her beds so I cant mow it. It was ripped out about 4 weeks ago and it is already about 6 feet tall. I can cut it with a string trimmer because it is coming up through her bushes.

    Only option I can see is to spray it with crossbow unless I can find an effective organic herbicide.
     
  4. RigglePLC

    RigglePLC LawnSite Fanatic
    Posts: 11,938

    That is a toughie! It may work--IF--you cover the good bushes with a plastic bag. Spray with vinegar, hot steam, exhaust from your mower, ammonia, whatever you can think of.
    Then with rose pruners or scissors, cut off new shoots of the knot weed every week to keep it less than 6 inches tall. You may wish to use Octane or Quicksilver--both are about a hundred times safer than Weed B Gone. You only need about 3 milliliters per gallon.

    If this is not practical. Remove bushes. Kill whatever you can and lay sod. Keep cutting it short. Plant bushes in big decorative pots.
    Just my opinion...YMMV.
     
  5. upidstay

    upidstay LawnSite Bronze Member
    from CT
    Posts: 1,293

    I like to use some good organic Round Up on knot weed.Sorry, but it has been my experience that the devil himself grows this stuff, and nothing short of ALOT of round up will take it out. Yes, cutting it short will eventually take it out, but it will take a long time. Years. The roots go down feet, and all it takes is a little piece for the plant to regrow, so I doubt if a burn down will work.
     
  6. OakNut

    OakNut LawnSite Platinum Member
    Posts: 4,070

    Posted via Mobile Device
     
  7. OakNut

    OakNut LawnSite Platinum Member
    Posts: 4,070

    Mow it to kill it? That's just silly

    I mow a patch of that evil stuff weekly. Every week there's one to two more feet of new growth from the stubs I left behind.

    Good luck. I don't think "organic" is gonna cut it.
    Posted via Mobile Device
     
  8. metro36

    metro36 LawnSite Silver Member
    Posts: 2,412

    Yeah, I gave the lady the option to have me spray with some sort of organic and remove everything, but I explained that I cant really quarentee sucess. I also had my spray guy price out spraying the whole area with crossbow. I have knotweed at a few other accounts and 2-3 apps of crossbow seems to do a good job of killing it.
     
  9. upidstay

    upidstay LawnSite Bronze Member
    from CT
    Posts: 1,293

    Thinking more about this, and again, I doubt if anything organic will kill it. Oh, you''l keep it at bay for a little while, but it'll be back. A guy down the street from me had a HUGE patch of it. He cut it down with a sickle bar, then covered it all over with heavy black plastic, staked it down then mulched over it about 6"with wood chips. A month later, the evil stuff had poked through the plastic and chips, and was happily taking the area over again.

    There are some things you are nice with, and use a kind, gentle approach. Other things, like japanese knotweed, you take off the gloves and use everything short of a nuke to take it out. You either use pesticides, and strong ones, or learn to like knotweed.
     

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