How to Eradicate Giant (and I mean GIANT) Japanese Knotweed

Discussion in 'Garden Pest Management and Identification' started by artnerd, Mar 28, 2006.

  1. artnerd

    artnerd Active Member

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    Back in the Kits lowlands, in my new yard, to my absolute delight... I have inherited a 10' tall Giant Japanese Knotweed. (Judging by last year's dead growth). It's just starting to emerge now, and I need to get rid of it, it's taking over my yard and the neighbours'. Boy are they happy we moved in, the previous "landscaper" had left it to grow this indelicate proportion... you can see where they've been hacking it back on their side of the fence...

    Problem is, it's a 4' wide clump, growing right against an large old tree stump, & in between huge roots so I can't dig it out. The canes are 1" thick or more. Frikkin' huge! That leaves chemical controls, but I want to grow veggies in the same yard, (@ 20' away, but in the direction of drainage on heavy clay soil), and I don't use pesticides or herbicides anyways, except as a means of absolute last resort.

    So, anyone know any natural alternatives? If I start pouring jugs of vinegar on it now, will it be gone in time for the Olympics??? Ideas?

    Thanks!
     
  2. Ginger Blue

    Ginger Blue Active Member

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    Roundup is the greatest labor saver on the planet. I'm a huge fan of its judicious use. If used properly and with care, it will not hurt anything else. It's not dangerous past the drying time and breaks down to inert things so the soil isn't harmed. It is absorbed through the plant's leaves and causes the blockage of food transport in growing plants. The killed plants are also not toxic. But you gotta make sure you put it only where you want it and nowhere else. It will kill anything it touches. And the overspray will kill or maim nearby plants if you're not careful. I've had good luck applying directly to leaves with a sponge paintbrush.

    Considering how persistant knotweed is, I wouldn't but too much trust in natural remedies. This is a time for the big guns. Save the vinegar for your dandelions.
     
  3. Eric La Fountaine

    Eric La Fountaine Contributor UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    Unfortunately I think Ginger Blue is right on this one. It is a serious pest. If you cut it down it springs up from the roots and will spread in all dirrections. I am looking at removing some huge clumps myself. I have not done enough reading, but I read a page that advised injecting herbicide into the base of the plant as it begins its spring growth. The page said it would take three years of this to erradicate the plant!

    I would read up on this one before trying to kill it. It would be awful to try to cut it down and only end up encouraging its spread.
     
  4. Gordo

    Gordo Active Member

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    One tip I remember about Round-up use involves using an empty yogurt or cottage cheese carton. Half fill with solution, cut an x in the lid, and insert branch tips of the weed to be eradicated into solution. This is supposed to work especially well for persistent weeds which spread by roots.
     
  5. Dixie

    Dixie Active Member

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    you can also use a sponge type paint brush to apply the round-up on the fresh cut. that way you will definitely apply the chemical to your target and nothing else.
     
  6. NiftyNiall

    NiftyNiall Active Member 10 Years

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    Vinegar will not work, the plant actually creates an acetic environment for itself. Round-up, full-strength applied to the cut stems in the fall,(5-15ml.) when the leaves are moving the nutrients, down into the roots is the most cost/time effective way, injection works, but is not really for home use$$$. It may take three years to eradicate,(sometimes even after applying three times per year!)
     
  7. Just Curious

    Just Curious Active Member

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    I'm trying mesotrione on it this year. So far it's grown through one application but I've applied it again this week, one can only hope.
     
  8. artnerd

    artnerd Active Member

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    Thanks for all the suggestions everyone.

    After digging up 10' tall parent plant, pulling 2 rounds of new plantlets, and digging out another round, 2 bottles of the evil Round-Up and one of a "natural" herbicide, it laughed at us.

    That corner of yard now under landscape cloth & 2 inches of gravel. Hah!

    (It will probably just grow out to the edges...sigh).
     
  9. Margaret

    Margaret Active Member 10 Years

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    I am tempting the gods by saying this but I have so far excaped this dreaded plant. Was just looking through the posts though and wonder that if it likes to be in an acidic area would it be weakened/ discouraged if the ph of the soil was changed?
    Just a thought.
    Margaret
     
  10. dawnh

    dawnh Member

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    Not sure if you're still looking for suggestions on how to eradicate your knotweed, but thought I'd let you know of some work that we've been doing to eradicate large knotweed patches at Jericho Park in Vancouver.
    We're working on getting the equipment and permission to do herbicide stem injection (the only noted way of eradicating knotweed on a long term basis) but in the interim have been working on ways to at least slow its growth. After two years of cutting, pulling, digging and other variations, the best treatment we've found is to cut back the knotweed each time it reaches about 10 cm in height (about every two weeks). Patches that were once dense and three metres high now are much more sparse and rarely get higher than a metre after a month. We've also noticed that where there is other vegetation -- tree saplings, horsetails, ferns, blackberry, the knotweed is beaten back even more.
    For a good review of knotweed and how to control it, check out The Nature Conservancy's abstract at http://tncweeds.ucdavis.edu/esadocs/polycusp.html. Although it is for Japanese knotweed (Polygonum cuspidatum), all the same principles apply to giant knotweed (Polygonum sacchalinense) and Bohemian knotweed (Polygonum bohemicum) – a hybrid of the two.
    If you'd like more references or info, just let me know.

    Dawn
     
  11. Michael F

    Michael F Esteemed Contributor Forums Moderator 10 Years

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    One other non-chemical option, if there aren't any other valuable plants nearby, is goats.
     
  12. Daniel Mosquin

    Daniel Mosquin Renowned Contributor UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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    Thanks Dawn - appreciate your input!
     
  13. fern2

    fern2 Active Member

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    What about cutting it back to ground level and then covering it with thick black plastic that extends several feet past the plant's current reach? That would block its ability to photosynthesise. I realise that the knotweed might try to stretch roots or creepers past the plastic's edge but, if you're careful to stay on top of those too, I think you could at least do some serious damage to the plant over the long term. I believe that that's what someone (park's board? UBC researcher?) has been doing in Pacific Spirit Park lately, along the main trail off Imperial. Last time I checked, it seemed to be working fairly well.

    PS: RoundUp is horrible stuff (for you, local ecology, & the global economy - for more info, do a google search for 'Round Up' + 'Monsanto') and, personally, I'd avoid it like the plague. Seriously, I'd rather ENCOURAGE the knotweed than use RoundUp...

    Good luck!
     
  14. jerik

    jerik Member

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    From Japan here:

    I would never, and I mean NEVER encourage knotweed. It can punch through 4 inches of pavement. It's roots also can run under a highway, and a little 2 cm piece of root can sprout on you. I'd clean out all the old stocks so you can see what is there. Cut off all the living stalks and make darn sure they don't have a chance to root in your compost pile. Then I'd hit it with roundup when it is just poking out of the ground, and go back every 2-3 days to do it again on any other new shoots. IMO you and your neighbors should inspect everything within a 20 foot radius.

    Maybe some forum member should try to isolate the gene that makes it grow so fast and try to splice it onto something else like a western red cedar.

    Good luck
     
  15. jimweed

    jimweed Active Member

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    Unfortunately for the original poster of this thread, herbicides are out of the question now because of the City of Vancouver's pesticide bylaw. I can see why so many people have no luck with spraying Knotweed, they're using Round up.

    Anyone ever tried 2,4-D or Amitrol-T on the small shoots? Then applied Simizine or Casoron or even better Picloram to the effected area? There are ways of controlling this plant, it's called $$$, and using the effective products.

    These products are not advisable for the home owner, but if anyone in the agricultural or weed control business is reading this because there Round Up job doesn't work on it, consider researching these products. Jim.
     
  16. Ron B

    Ron B Esteemed Contributor 10 Years

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    A plant that is prevented from storing food can't grow after a certain point. I think with persistent perennial weeds like this much of the time the difficulty experienced with attempting eradication through decapitation is lack of diligence. No plant can grow faster than a person can move. If all shoots are removed promptly for a period of years a stand simply MUST become starved and die out.

    Many down here are the sterile hybrid so these would not have generated a large amount of seed from which new ones would be growing after the parent clump was killed. Of course, the parent clump did come from somewhere and might be replaced at some point from new seedlings coming in from off the site - if any of these should appear and be overlooked or ignored before becoming fully developed.
     
  17. lots of apples

    lots of apples Member

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    I completely agree. It's a real dilemma: on the one hand, here is this noxious weed that is becoming ubiquitous in urban and forest areas, introduced either intentionally (through ignorance of what non-native plant species can do) or accident (seeds and spores travelling in soil or on feet) and is causing widespread devastation and seems impossible to eradicate...
    and on the other hand we have this noxious commercial chemical product, whose use is also becoming ubiquitous through ignorance ("gardeners" who want an easy alternative to pulling weeds) and aggressive marketing ("Just use Roundup and there'll be no weeds!) which is also causing widespread devastation (in the form of cancer and groundwater contamination and causing plants to evolve to be resistant to herbicides thereby causing the need for stronger chemical herbicides), the use of which, alas, also seems impossible to eradicate.

    There is a website based in Europe (I think) that advocates biological control of this problem, as being somewhat risky but in the long run far safer than poisoning our parks, forests and neighborhoods with more Roundup: www.cabi-bioscience.org/html/japanese_knotweed_alliance.htm
     
  18. pjtitangirl

    pjtitangirl New Member

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    I have tried most of what is suggested in this thread. Has anyone tried sulfuric acid? I have a patch of this terrible that is about 600 square feet and is on a rather steep slope. I am currently cutting down the old 'wooden' plants left from last year. and am experimenting with different solutions to kill or at least inhibit the new sprouts. also - I don't have a lot of money to spend on this project. PLEASE HELP!!! any advice is appreciated.
     
  19. Daniel Mosquin

    Daniel Mosquin Renowned Contributor UBC Botanical Garden Forums Administrator Forums Moderator 10 Years

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  20. ddrinnan

    ddrinnan New Member

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    I wish you luck (2" of gravel & all). But let me tell you... it took me 3 years of physical (cutting down) and spraying (with Roundup, which I detest as a product) to get my Japanese Knotweed under "control". I started 17 years ago (1998), and was vigilant for 3 years. But because I didn't continue being vigilant (due to acquiring chronic Lyme Disease), I'm STILL battling the same stands of knotweed... though now it's a much easier battle... depending on how many times a year I attack it.

    Considering my lapses in eradication (due to the Lyme Disease), I'd say that a concerted effort to eradicate it using Roundup (which, did I mention I detest?) would probably have taken 4-8 years, had I remained vigilant & committed. :-/

    By the way... for these last several years, I've been using Roundup Pro (50.2% glyphosate), mixed to roughly a 9% mixture. Recent articles I've been reading have been more advising a 100% mixture (i.e., full strength)... though I've also read that using it TOO strong doesn't work either, in that it doesn't allow the product enough time to work its way into the plant's root system... where it really needs to do its work.

    Digging up the root cluster/knots is supposed to be useful in the process, but that's physical and time consuming. Plus - it's not a 100% solution; it just slows the growth down. Aggressive vigilance and spraying/injecting seems to be the best strategy.

    For what it's worth... I've read that the roots of this plant (which are the real problem) can grow down as far as 3 feet, and as far away as 60 feet. So unless you get it all, it can still pop up somewhere else. :-/
     

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