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Japanese Knotweed 😩

  • 04-08-2021 8:48am
    Registered Users Posts: 17,905 ✭✭✭✭ _Brian

    Having to tackle a few decent stands of this shiite. Thankfully not at home place but has to be done

    Have held off spraying until now. Plan is to spray it 3-4 times now before end September.

    Grazon90 or Roundup, have both to hand.

    love to hear some success stories



  • Registered Users Posts: 1,763 ✭✭✭ Lime Tree Farm

    Don't know anything about knotweed, but do know that plants use a lot of energy to produce flowers. Cut back hard after flowering, allow approx 3 weeks to recover ( the plant, not yourself) then hit it hard with a brushwood killer. You need a full 24 dry day afterwards, to get maximum effect.

  • Registered Users Posts: 25,512 ✭✭✭✭ Dempo1

    Awful stuff and make sure your well covered up. Knotweed seems to be very resilient against most weed Killers but I've heard Grazon90 pretty tough.

    I've not come across much of this weed here in the Midlands but I was in rural maryland, USA for a few years, it seems there approach was spraying but afterward they dug up roots.

    Good luck, just be careful, I believe it can give a nasty rash 😉

    Is maith an scáthán súil charad.

  • Registered Users Posts: 10,070 ✭✭✭✭ wrangler

  • Registered Users Posts: 390 ✭✭ PoorFarmer

    I injected Roundup Biactive into the stems 3 years ago. Small bits of regrowth since only. Will struggle to control it here though as I have it on the riverbank and it keeps getting washed down to me

  • Registered Users Posts: 1,763 ✭✭✭ Lime Tree Farm

    The cursed plant around here is old man's beard. Although I have seen it in flower arrangements and it's lovely.

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  • Registered Users Posts: 17,905 ✭✭✭✭ _Brian

    About 5 years ago we had a bunch of horsetail appear at the end of our lane after digging and filling with stone.

    on the recommendation of a friend I used a combination of Grazon90 and mcpa mixed and it knocked it out in one application, I’m not keen on mixing chemicals but am tempted to try this again.

  • Moderators, Social & Fun Moderators, Society & Culture Moderators Posts: 25,260 Mod ✭✭✭✭ looksee

    Japanese Knotweed (and Giant knotweed, which is similar) will not cause rashes - though it can cause minor irritation in some susceptible people, which is true of many plants. Giant Hogweed is dangerous, but a completely different plant.

    also check out this site/pdf

  • Registered Users Posts: 464 ✭✭ ABitofsense

    I've being spraying 2 spots on the farm for about 5-6 years now. Father at the time didn't know what it was until I told him. When I started I had to be lifted using the tractor loader to spray it it was that high. Thankfully it's only small shoots in the 2 spots which I spray each summer & Autumn. It never spread any further or massive growth since

  • Registered Users Posts: 5,546 ✭✭✭ Blaaz_

    We mixed brush spray and roundup earlier in year on rented ground and it hasnt come.back after could see exactly,where we ran out like

    Another patch has been hit 5/6 times with grazon 90,and only starting to slow down regrowth now.

  • Registered Users Posts: 79 ✭✭ maconof

    Spotted the JKW on a small patch at the far corner of our farm 4/5 years ago. It must have been 8 foot high at least and covering 20 square metres. Roughly 100 or so shoots coming up from the ground. The first year we sprayed Roundup early in the year in April to reduce the growth throughout the growing year and then sprayed in mid-September to get it into the roots for Winter. There was probably 3/4 the amount of shoots the following year.

    Each year since we've used Forefront T (using same application method as Roundup) and finally this year we're down to 1 shoot. We switched to Forefront T as it doesn't kill the grass around the area, so less bare ground for new shoots etc. It uses two chemicals (aminopyralid and triclopyr) instead of Roundups one (glyphosate).

    Also, I see a suggestion above to cut back the plant, would heavily advise against this as even the tiniest of fragments from the plant can cause new growth. The local council decided using a hedge cutter on a local road with some JKW was the best course of action and now there's a good 1 mile stretch of JKW that's now sprayed every September instead.

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  • Registered Users Posts: 464 ✭✭ ABitofsense

    Yeah as above definitely don't cut that's how it originally moved on out farm from one point to the other. An old wall was taken out that had a small bit of it (originally sown as garden plant long time ago) & took of from there. After the 1st year of spraying, I gathered up all the shoots of dead material & burnt them just encase. I hate the stuff!

  • Registered Users Posts: 493 ✭✭ Billgirlylegs

    Definitely do not cut it. Can you spray in situ and then burn (ie petrol) the dead stalks and stems as they stand.

    Avoid moving it or other material close by. Avoid grazing nearby if you can.

    Best of luck with it

  • Registered Users Posts: 9,467 ✭✭✭ patsy_mccabe

    We had a patch here about 5 years ago. I sprayed it with Roundup (Glyphosphate) in August for 2 years straight and then I forgot about it. Noticed this year that a smaller patch is starting to grow again.

    So as above, don't cut just spray in August, as advised by the experts.

    " And on the riverbank forgotten the river's name."

  • Registered Users Posts: 10,043 ✭✭✭✭ Danzy

    Hedge cutter went at one stand near here a few years ago, the whole length of the cutting that day has it in groups now.

  • Registered Users Posts: 803 ✭✭✭ bb12

    had patches of it here and there. the thing with knotweed is not to touch it in any way such as cutting, digging up etc as that will just make it worse. a strong glyphosate mixture always works for me and i've pretty much eliminated it everywhere now

  • Registered Users Posts: 1,446 ✭✭✭ Seanergy

    To try something new, I bundeled up a small patch of JNW into zip lock bags this month. It takes a bit of time to do this, espically if you do not want to break any of the stems/leaves, but the JKW was amongst some plants I did not want to harm.

    Filled about a dozen bags before pouring in some glyphosate. Most of the bags have gone full brown now, so presuming roots too, will top up any of the bags that didn't brown fully again.

    Haven't heard of this approach, time wil tell.

  • Moderators, Society & Culture Moderators Posts: 12,024 Mod ✭✭✭✭ blue5000

    Warm, sunny August afternoon and sprayed with Roundup worked for me. Don't cut or dig it.

    If the seat's wet, sit on yer hat, a cool head is better than a wet ar5e.

  • Registered Users Posts: 17,905 ✭✭✭✭ _Brian

    I’ve seen this done with bindweed with very successful results.

  • Registered Users Posts: 11,080 ✭✭✭✭ Nekarsulm

    Big stand of it at the gates of our girl's school, between the lane way and the local river.

    Nobody doing anything about it, so I hit it with Glyphosate one Sunday morning last September.

    Got a good kill on what I could reach, and I'll hit it again in a month.

    Might try mixing the two chemicals this time.

  • Registered Users Posts: 68 ✭✭ twofish101

    A bit of reading on the subject

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  • Registered Users Posts: 17,905 ✭✭✭✭ _Brian

    Reading the label on a bottle of roundup yesterday and it recommends 60ml/litre for knotweed.

    Bit of dry weather on forecast for next week so I’ll tackle it then.

    it turns out it’s Himalayan Knotweed rather than Japanese. Same problems though just different shaped leaves.

  • Registered Users Posts: 762 ✭✭✭ oldsmokey

    Roundup,ll kill it, just watch out, the rhizomes could burs into life several years after you reckon you’ve the hoor killed. It can be done though…I sprayed it in may and sept, and really wet the earth at the base

  • Registered Users Posts: 5,591 ✭✭✭ saabsaab

    Don't cut or burn it. A good spray when flowering should kill it..repeat for a few years as necessary.

  • Registered Users Posts: 1,209 ✭✭✭ Barktastic

    If you dont want to go down the spray route you can go for smothering.

    Cut the plant a few times this time of year before it goes to seed and bag it, it will die in the bags.

    The plant is shoots are edible, supposedly rich in resveratrol.

    In October when it dies back cover the area with cardboard, then a weed barrier (quiet reasonable in hardware shops) and finally a bit of topsoil.

    Spraying can kill it but it can go dormant for a few years and come back. If the rhizomes are starved by not being able to grow plants it will die off under ground.

  • Registered Users Posts: 17,905 ✭✭✭✭ _Brian

  • Registered Users Posts: 5,546 ✭✭✭ Blaaz_

    How many years would the rhizomes live for dormont under the ground?

  • Registered Users Posts: 14,122 ✭✭✭✭ Donald Trump

    In theory, are the councils supposed to come out and take care of it? I knew a fella who was working for a private company who were doing it for the Councils a few years back. That was more for people's gardens but I think the principle was still the same.

    There is a verge not too far from me that the Council put up signs saying knotweed was present and reminding it's workers not to cut the get a good view of the signs every year after they come along and cut it. (It's one of the few that they actually cut.)

  • Registered Users Posts: 317 ✭✭ What.Now

    Please do noy cut it. You will be aiding the spread.

  • Registered Users Posts: 1,209 ✭✭✭ Barktastic

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  • Registered Users Posts: 1,209 ✭✭✭ Barktastic

    Yes, the cutting cant be done with a strimmers, needs to be precise, bagging everything