Monday, 2 December 2013

Control of Japanese knotweed in the private garden



There is no doubt that Fallopia japonica - it used to be called polygonum - is a very serious weed. Its elimination can cost hundreds of thousands of pounds on a single building development. 

It is not difficult to control in the private garden, but you must not take your eye off the ball and it will take time. If you have the misfortune to possess a strong growing clump it will take at least three years to clear it using herbicides.
Without herbicides it will be a complete nightmare, but with much persistence and a great deal of effort you can still achieve complete control. 

I do advise that you eliminate this plant. Although it is not unattractive and you might feel it not to be a problem, beware! You might find yourself with some very expensive provisions if it gets into your neighbour’s garden and, should you or your neighbour want to build an extension and planners become involved, well need I say more? It’s best to quietly get rid of it before it ever becomes an issue. Some people are now frightened that it can even affect the value of their own property.

It will normally take at least three years to get rid of a strong clump of Japanese knotweed by spraying with glyphosate. It’s worth repeating what I have previously said about a principle that applies when eliminating difficult perennial weed - the actual work involved is quite small, it’s just that it is spread over a long period of time! 

In my own case, in Worsbrough cemetery garden, I eliminated a vigorous quarter acre stand of luxuriant ten foot high knotweed, but it took ten years. It took me two years to ‘break the back’ of the problem and I then lost focus. The area just became part of my less intensive spraying routine.

I propose to describe my own methods and the very exciting recent success of Peter Williams in a garden in Derbyshire.

About Japanese knotweed

Native to Japan, it grows on Mount Fuji above 2400 ft and is an efficient first coloniser of infertile volcanic slopes. It make me wonder how such a vigorous plant obtains its nitrogen. The Japanese call it ‘itadori’ which means ‘healer of the sick’, and I recently read how its shoots can be used to make a very fine gin! So much for hysterical claims from the Ministry that you should wear protective clothing, a mask and generally look like a spaceman and terrify the local population just to burn the tops

It is however a pretty tough cookie. On volcanic slopes it grows close to fuming fumeroles. No wonder it can take over a garden or claim large tracts of riverbank and wet ground in the wild. It has a fantastic ability to smother and kill competing vegetation. This plant really is allelopathic and exudes plant killing toxins.

The problem of Japanese knotweed has become worse where Fallopia japonica has  hybridized with other vigorous knotweeds such as the Russian vine, Fallopia baldschuanica. This is rather similar to the problem I wrote about recently with the hybrid Rhododendron x super-ponticum.

Sources as reputable as the Environment Agency will tell you that the weed can spread as much as a meter a month and grow more than 10cm per day. It is surprising how quickly plants grow under optimum conditions. Just google how far common creeping thistle will spread in a season! Yes, Japanese knotweed will spread very quickly in a wet month in August when there is no competition and yes, it will shoot up to ten foot high in very few weeks in June and July. Plants commonly grow rapidly in short vigorous bursts but then stop. Yes, it is a very real problem and has the ability to speedily spread, but I do find the propaganda hugely overstated.

There is a rumour that it is illegal to plant Japanese knotweed in a garden. I wouldn’t recommend it, and it is definitely illegal to introduce it into the wild. It originally became a problem because it was introduced as a garden plant. A few years ago I visited a botanic garden (not one in God’s county) and admired their magnificent Polygonum japonica (as it was then called). The plant was confined by a lake on one side and a broad band of regularly mown turf on the other. Absolutely superb.

My experience in Worsbrough cemetery.
I explained in an earlier post how nearly twenty years ago, with the help of the naughty boys on probation who were  doing community service, I eliminated more than acre of six foot high brambles in the wooded cemetery. Within the overgrown jungle was an irregular clearing of a quarter of an acre of very well established Japanese knotweed. The colony was bounded by a sturdy cemetery stone wall, trees and brambles. It was virtually impenetrable and grew as strongly as on any riverbank in Wales. I make one visit per month and in the first few years I had other ‘fish to fry’ and completely neglected the knotweed. It remained confined, I did nothing, but it did not spread much further.

Eventually I got round to the fascinating horticultural challenge to kill it. I started on my project at the ideal time in late June when it had achieved maximum height and the leaves were still soft and receptive to my glyphosate. The literature does not confirm my opinion and says that translocation is more effective later in the season. I agree this is true of some translocated herbicides but not glyphosate. 

Japanese knotweed has a very limited season, not emerging until after severe Spring frosts and making no further growth after Autumn frost arrives. I would be able to spray about three times a year.
As Is my wont when faced with difficult weeds on the first occasion of spraying I used my glyphosate at the maximum permitted concentration (and a little bit more) and gave them a drink in the morning and for good measure another later in the day. It was not possible on that day to reach all the weeds with my knapsack sprayer, even with its extended lance. I was aided in my efforts that the clump was irregular in shape  and I could get in at the edges. I sprayed three times that season. The three sprays took in total, about six man-hours. I did the same in the following year. By the third  year strong new growth had ceased and ‘bonsaied’ new growth was only about a foot high. As far as I was concerned, ‘job done’ and the site only received my normal maintenance spray. The knotweed did take another eight years to be completely eliminated but I am certain had I continued with my former intensity it would have been completely killed by the end of the third year.

It is rather ironic that other than Keith Burkinshaw the cemetery sexton, hardly a single Birdwell resident knew that they had a Japanese knotweed problem in their locality. They were certainly unaware that I had solved the problem for them. Nobody noticed!  St. Mary’s Church community pay me generous travel expenses for my monthly visit and pay for my glyphosate but the marginal cost to them of eliminating the weed was zero.

That will be £50,000 sir!

In contrast I received an anxious phone call from Bolton Percy church warden that someone had spotted knotweed in the cemetery and there was a bit of a local panic.The cemetery has never seen Japanese knotweed. The plants that had been spotted were completely harmless Polygonum persicaria that I planted.

Peter Williams’ exciting success in a private garden…. somewhere 



Application by injection is not a new principle. It worked very well for Peter this Autumn. The problem was that there were a few very healthy clumps of knotweed in someone’s garden. Some metres away there was to be a new building extension. There was not a cat’s chances in hell of the knotweed harming strong new building foundations. Unfortunately the plants reputation to penetrate badly laid or crumbling tarmac and its acknowledged ability to penetrate cracks made it wise to eliminate it.
This is what he did.


He drilled the base of each tough stem and injected a 10% glyphosate solution. This was at the beginning of September. The quantity of the weed was about twice that in the picture and it took him two hours. I asked him if the method would translate to larger plantations and he said no, it was too labour intensive, he would spray in such circumstances.


One month later the top of the knotweed was dead and he cut it back to the ground. None of the surrounding ornamental plants suffered any damage what-so-ever. For practical purposes the knotweed was gone until next June! 
Now the question is will it come back? Almost certainly yes, and the knotweed must be allowed to grow a new top before it is re-treated, perhaps the then much weakened and smaller knotweed will be sprayed.
I have no experience of Peter’s method. Wouldn’t it be wonderful if the Japanese knotweed has been killed outright. I doubt it, but I will keep you informed.



Does digging out roots help?
No digging was done at Worsbrough and I do not imagine Peter intends to dig either. The professional literature suggests that a combination of root removal and spraying is best. This might well be true but it is very important that you spray the undamaged intact weed first.


Further technical and legal information provided by Peter Williams and quoted verbatim 

Hi Roger

Looks an interesting article and I assume you have some pictures of the foliage to show just what a beautiful plant it is. You might refer at slightly greater length to the timing of spraying or injection - The sources I looked up all stressed the need to spray late in the growing cycle when nutrients were being translocated back to the roots for overwinter storage. I used just a few ml of glyphosate per shoot and as you say nothing in the area was affected even the grass growing very near the clumps.
Its distribution is also possibly worth a mention - whereas it is very widespread throughout Britain (as shown by the national 10x10km grid square data) it is only locally very common and usually in past industrial sites ( as shown by reduced presence in 2x2 km squares).
Interestingly Edward Salisbury in the classic work on weeds in 1964 (2nd Ed) hardly mentions this plant but he does quote  the RHS journal ‘The Garden’ for 1897 thus "A plant of sterling merit, now becoming quite common...and is undoubtedly one of the finest herbaceous plants in cultivation". He goes on to comment that that reputations can be lost and it can be seen on waste ground in London and once established "it is a labour to eliminate".
It might also be worth mentioning the Cornwall County Council website that is helpful without being over dramatic and does I think, cover all the legal issues.
Best wishes
Peter

Japanese knotweed (fallopia)

Not just a weed but a biohazard. Introduced from Japan mid C19.  In
Japan it does not cause problems because of its natural pests  and
predators.  These were not introduced with the plant into the UK.
Noted in wild in London 1900, Exeter 1908 and Suffolk 1924. Cornwall
1930. By 1960’s Land's End to John o Groats and beyond to the isles (isle
of Lewis?).  Although it flowers, spread is vegetative - roots
extend 2 m down and 6m laterally per year. (p263).  Spreads in urban
areas/churchyards  but not in ancient woodlands or grassland or
agricultural land.  Japanese knotweed is listed on Schedule 9, Part II
of the Wildlife and Countryside Act 1981 making it an offence under
Section 14 (2) (a) of the Act to "plant or otherwise cause Japanese
knotweed to grow in the wild". Both the Police and local authorities
have enforcement functions under the Act. Penalties for a Section 14
offence have been modified by the Countryside and Rights of Way Act
2000 for England and Wales. A magistrates’ court can impose a maximum
fine of £5000 or a maximum prison sentence of six months, or both. A
Crown Court can impose an unlimited fine or a maximum prison sentence
of two years, or both.

Under the Environmental Protection Act 1990 above and below ground
parts were classified as 'controlled waste' and have to be disposed of
in licensed landfill sites only.   The fear and legislation relating
to this species led to the establishment of a specialist industry
aimed at its destruction. The industry stressed the dangers of the
plant and pointed out the difficulties not only of killing the weed
but also its subsequent disposal. Public authorities and worried
private citizens employed the contractors and business boomed.  This
developing 'pest removal' industry received another boost in 2009 when
the Finance Bill allowed companies tax relief of 150% on the cost of
removing knotweed from contaminated land. The price for clearing the
weed rose to above £50 per square metre and the annual cost in GB in
2010 was in excess of £150 million. Clearing the Olympic site cost
£70 million.

Thank you Peter You have given much food for thought.

Update November 2014
In response to recent hysterical Government legislation I am writing a further post about Japanese knotweed next Spring. In the meantime a few further thoughts...

My mention that the hybrid between Japanese knotweed and the Russian vine might be a problem is probably nonsense. I have reported elsewhere that the best known hybrid is a complete wimp!

There has not been a single sign of Peter’s injected Japanese knotweed returning and there has been zero damage to surrounding plants. I deliberately ‘miss spoke’ about his glyphosate concentration. Although he only injected a very few ml of the chemical it was actually almost neat 360g/l commercial product!

My  concentration of spray for my own spraying against Japanese knotweed in Worsbrough was 1 in 50,  360g/l concentrate/water. I mixed this by adding 200ml of 360g/l glyphosate concentrate to ten litre of water in my knapsack sprayer.

A number of interesting have arisen in my comments section. Just press the comment button!

52 comments:

  1. We had this growing on the edge of our allotment plot but fortunately the council dealt with it. There was some growing alongside the house of a lady of 90+ on land belonging to Leeds council which I reported to them but they seemed rather unconcerned and just gave me suggestions as to how I could remove it to which I replied it's growing on your land and is your responsibility!

    There was a case where a plant emerged through the floorboards of a house too which may I suppose say something about how the house was built!

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    1. It is certainly an aggressive plant Sue, but its not the only one and others don't get as much hype. I frequently see tree roots busting up tarmac and poplars can be a real nightmare.
      My Hydrangea petiolaris and my vine regularly invade my garage interior.

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    2. I have read your blogs about this plant Sue
      I think it's aggression is a different kind of problem
      I do have this plant in Bolton Percy cemetery, but I did not put it there!
      (Don't tell anyone but I am in the nectar camp, I like it!)

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    3. I think it's only a problem in river banks. We have a patch just outside the gates of our allotment site which doesn't cause a problem.

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  2. Excellent post Roger, I have never suffered the intrusion of Japanese Knotweed but I am inclined to think that, like many things today, the problem is somewhat exaggerated. A telling quote from Peter's excellent information is "The industry stressed the dangers of the plant and pointed out the difficulties not only of killing the weed but also its subsequent disposal." To misquote Randy Mice-Davies "they would say that wouldn't they"! One of the biggest problems is that we as competent gardeners forget that the majority of the public have no idea what Japanese Knotweed is so those who are completely ignorant let it grow regardless whilst those who recognise it, probably due to the media, immediately panic and call in expensive contractors.
    On a different tack, is Himalayan Balsm going to succumb to the same disease that has devastated our bedding Impatiens or can it be used to breed back resistance?

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    1. You have certainly been exercising the little grey cells Rick!
      I think the politically incorrect Himalayan Balsam has so many detractors that there might be a wish to transfer the downy mildew to it. I suspect that although both are the genus impatiens they are genetically fairly distinct. I do miss busy lizzies!

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  3. My neighbour tried a similar stem injection method. She cut them off just above the lowest node, pierced a hole down through the node to the lowest hollow section, and filled. It was only a small clump of knotweed, but one she had been ignoring for a few years. She treated it in Autumn 2012, and said it didn't come back up in 2013.
    Unfortunately there are two other neighbours who are still ignoring it, and unless there is a combined effort to tackle it, it will just keep moving about. Hopefully not in my direction!

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    1. Thanks Sarah, Peter will be delighted if it does not reappear next year. I expect Deane Forde might suggest it has just shut down and your neighbour will have it back next year.

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  4. The Knotweed in the case did not need to take 8 years to eradicate! The fact that you used more than the recommended concentration (which is also illegal) means that you made the plant shut down and sent the plant into a bonsai state and has not eradicated the problem, so in fact the way it has been treated has meant that it has taken longer than it should of done!
    It would not be a problem at all eradicating the Knotweed in 2 years and this would not affect the surrounding vegetation at all- we spray next to TPO trees all of the time.

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    1. Thank you for your comments.
      Perhaps you did not note the irony in me taking ten years. I did claim that had I carried on in year three as I had started it would all be gone at the end of three years. My normal method of weed control for general weeds is to spray with a regular spray of about 1 in 100 dilution and at that part of the cemetery I get round every two to three months.
      What on earth do you mean by the plant shutting down? In the third year I referred to the new growth of the Russian vine as bonzaied, i.e. dwarf. It was about a foot high and its new leaves looked perfectly healthy.
      Its now four years since I eliminated the knotweed - and by eliminate I meet zero sign
      of any Russian vine growth whatsoever. If that is shutting down, it's good enough for me
      I am aware that using glyphosate too strong can be counter productive but at no stage was my spray stronger than 1 in 60.
      I do find maximum permitted concentrations perplexing when I find that reputable manufacturers recommend glyphosate concentrations as low as 1 in 25 for weeds such as marestail.
      I am impressed you can get rid of it in two years without expensive excavations. As my title says My piece is about private gardens and I am using glyphosate. You are perhaps using other professional sprays which I would not be comfortable recommending to the public

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    2. ps sorry about my freudian slip by wrongly stating 'Russian vine,' Deane

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  5. Off topic, and at the risk of causing an argument (or another one) please could I ask exactly what is illegal? I'm aware that anyone holding a licence needs to obey certain regulations, as do the manufacturers and retailers. But is it actually illegal to do whatever you like in your own garden?

    For example, Ammonium Sulphamate cannot legally be advertised or sold for weed control. Therefore it follows that it would be illegal for a professional weed controller to sell it as a service. But that doesn't automatically mean it's illegal to use it in your own garden, however you jolly well want to. Or does it?

    (personally I don't like the stuff, I can't imagine it does the ecosystem of the soil much good. But if it will get rid of the horsetail then it's worth a try!)

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    1. Yes Sarah, you have opened a can of worms! I have entered the fray myself in my post about moss killer where sulphate of iron sounds if its a similar case to your chemical ammonium sulphamate which is a stump killer and a fertiliser. Sulphate of iron is a fertiliser and a moss killer and it is probably illegal under the pesticide regs to sell it at as moss killer although you can sell it as a fertiliser even for your mossy lawn!

      It is probably illegal to spray stewed rhubarb leaves to kill aphid
      I was told recently that no one has ever been prosecuted for doing this or for using a fertiliser as a moss killer or a fertiliser as a stump killer!

      As to controlling mares tail that will be another post

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  6. Hi Roger,

    It's now 'next year' and i am wondering if there is an update on Peter's injection method. Did it work? how much re-growth was there?

    I am preparing to tackle some knotweed in the next month or so and would love to hear how peter got on and / or if there are any further learnings.

    Cheers,
    Andy

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    1. Completely successful Andy!
      Peter has been promising me a picture for a few weeks now and I hope to publish it next but one post. It shows distinctly healthy! herbaceous perennials enjoying completely healthy growth in total absence of knotweed!
      It is a very clear demonstration what a very precise application of glyphosate at very high concentration will do when injected into the stems of knotweed.- even though the total amount is quite small.

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  7. Hi Roger,
    Just started building on our new plot and have realised that there is japanese knotweed on the banking of the local rugby club. There is a small river between the banking and my plot which is holding it at bay, so far. Can you please tell me how to treat/kill it. Thanks John.

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    1. Hi John
      It won't grow across a river as opposed to a small stream where it might if it sometimes dried out.
      The chance of seed blowing over is zero but in theory broken off pieces might root if they floated across. The press overhypes the dangers from small pieces regenerating. It is surprisingly difficult to get small pieces to establish but where they do it takes several years of neglect for them to become a problem. I am sure you would not let that happen!
      Our hyperactive government threatens legislation that might be costly for the rugby club and you might have a quiet word with the groundsman about eliminating it.
      It is easy to eliminate by spraying with glyphosate but it might take a few years if it is well established.
      The groundsman will have available commercial glyphosate 360g and it can be sprayed at dilution of 1 in 50 on intact foliage.
      It might be too late now, albeit if still green and if you don't have a heavy frost very soon it is actually excellent to spray it today!
      Next year let it make strong new growth and spray, perhaps in late June. Repeat spray regeneration after about two months and maybe once more? It might take a year or two if the infestation is very well established.
      As I say in my article easy in terms of labour input but takes a few years before its gone!

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    2. Just a couple of further comments!
      I have been in W.Yorkshire today and seen still green knotweed - they would drink up glyphosate very well!
      I was initially a little perplexed that you asked about control when I thought I had already written about it. In fact this post does assume some of my methods described elsewhere. I have written about glyphosate extensively, just put 'glyphosate' into the search box at the bottom of the blog 'wallpaper'

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  8. Hi Roger,
    Forgot to add I am from Swansea and they have introduced an insect from Japan which which eats the sap of the plant with good results, so I've heard. Is there any hope of purchasing any of the said insects.

    John.

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    1. I doubt it yet but watch the press. It will take several years for this fly makes an impact and you will be rid of yours soon enough.

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  9. Hija Roger - After several hours on Google I found your EXCELLENT blog - straightforward honest advice. Most of the other sites seem quite 'scary' and over technical.
    Here in Nunhead London our garden and five others are all
    'infected' by this wretched plant - The Victorians have a lot to answer for!
    Earlier in the summer I dug a trench a metre deep and filled over ten bags - hindsight informs me this was not an ideal solution - a nieghbour got a quote £500 x 6 households to 'treat' however some do not have that finance available.
    http://www.bbc.co.uk/programmes/b04mv9gk - Jeremy Vine Show BBC Radio 2 Thursday 20th November discussed the issue and I was most impressed by the no nonsense advice shared by David Verdicchio of Epuk Ltd. He only had a few minutes but gave down to earth advice on spraying - however maybe due to time contstraint's there was no mention about cutting back the plants - QUESTION: After spray treatment is it advisable to dispose of the remains - if so how long AFTER treatment.
    My intention is to follow his advice and YOURS on a 'do it yourself' approach which I will share with all the neighbours.
    Two initial questions:
    1) Can you recommend some robust spraying gear?
    2) Disposal - Burning seems to be a serious contender - I would obviously purchase a decent incinerator - what is your opinion on this option?
    I will propose a collective purchase of sprayer - incinerator etc ie share the cost.

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  10. Morning Michael
    I see you have added your name to the patchwork on the right. Welcome aboard!

    You have really been dragged in to the hype about knotweed – it’s only a plant!

    PROTECTIVE GEAR You do not need to pretend to be a spaceman! Think of a little old lady buying a glyphosate ready mix to spray the weeds in her path.

    SPRAYER Unless you have more than say 40 square meters you need no more than a three quid hand sprayer as illustrated in my post called Glyphosate roundup last August- the bit on convolvulus at the end

    DISPOSAL OF DEAD TOPS What’s wrong with a small bonfire or putting them on the compost heap or even burying them. They must be dead of course but they will be a few weeks after spraying

    SPRAY Although you could invest in a gallon of commercial glyphosate on the net for about fifty pounds that will spray several acres and last you for a lifetime of gardening, why not just get a litre of Roundup GC (Stands for garden centre and indicates a rip off) that will be enough for perhaps 100sq meter of knotweed for the three years it might take you.

    Before you start, read my post very carefully and the above comments including to John just above and also the August post. Unless in balmy London your tops are still green and alive and you can spray them now (Very unlikely) then DO NOT spray them until they are large at the end of June. Just leave any dead/dying tops until Autumn when you can cut them away. They may regenerate at their tops but much more so at the base. Probably erratically as you sound to have chopped them about. DO NOT zap new shoots as they reappear, let them get big first. You will probably need three sprays a growing season for three years to be completely rid, although by year three they will be just little runts!
    Best of luck in your new career as a landscaper!

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  11. Hi roger
    please could you give me some advice if possible. My sister wants to give me some of her plants from a garden which has japanese knot weed. She says that she has changed the soil from the plants now in pots and thinks it is safe and free from the weed. How does the weed grow from pores and can it somehow attach it self to plants
    thanks

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    1. Japanese knotweed grows from seed anon but only rarely and it is not a normal source of infection.
      Your plants from your sister will be fine

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    2. Hi Roger,

      Many thanks for an excellent and informative article. I love the 'common sense' approach. Looking forward to tackling the knotweed!

      Can you please give me an easy to understand guide to the glyphosate mix. I'm new to gardening and dont understand the 1 in 50 mix etc.

      Thank you!

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    3. One answer is that it is all explained in my glyphosate posts - listed in the theme column on the right!
      I expect you don't want to trawl through them!
      My advice to mix at 1 in 50 assumes you are using commercial glyphosate - it says on the label that it is 360 gm per litre strength and is much stronger than the amateur product.
      I expect as you are a beginner that you are perhaps using the amateur product Ghalib.
      What 1 in 50 means is that when you mix up the spray you use fifty parts of water to one part of the concentrate
      The amateur product that garden centres sell is much weaker.
      This DOES NOT mean that when you make up a solution to spray that it is weaker than that made from the the commercial product. It just means that you need more of the garden centre concentrate to make up your diluted spray - and costs much more!
      Unfortunately I do not know the strengths of garden centre products - and they vary!
      The best advice I can give if you are using the amateur product is to make it up to the maximum strength recommended on the label - it will be the strength they suggest for 'difficult 'weeds!
      It might still be a bit early to spray J knotweed - let it make a big plant before you spray it

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  12. Thanks for all the useful advice here and time taken to write/post. I'm very grateful.

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    1. Letters like yours make it all worthwhile!

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  13. By spraying with glyphosate you probably eliminated the bees as well. I think the more laborious method of persistently removing it is definitely better.

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    1. I know no reports of glyphosate toxicity to bees!
      If you could see the hundreds of honey bees and bumblebees in my garden today you would not make such uninformed comment anon
      Of course dead knotweed does not provide much pollen and nectar.

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  14. Hi there. Could I ask if JKW can travel through a regularly mown lawn? We live near a railway embankment which is teeming with it, but we are separated from it by a meadow which is regularly mown by the council, and they weedkill the boundaries a couple of times a year. Should this be enough? I did have a small clump but I injected it three years ago and that killed it.

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    1. it would only cross a meadow over many years and you would observe its advance!
      No worries here Charlie
      A botanic garden in Cheshire has a magnificent one confined by a regularly mown lawn on one side and a lake on another!

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  15. Hi there, I have two small pieces of japanese knotweed on my driveway. I've sprayed it with roundup. How often should it be sprayed each year and when should I see it growing the following year. Thank you.

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    1. I cannot predict how often anon, there are too many variables! The ten foot high plants at Worsbrough would need to be sprayed three of four times when I started.( I now fail to find any whatsoever). A smaller plant in your garden might need two or three times. No good spraying when it is very small or brown and yellow. Wait for strong new growth to spray it and don't zap it at first appearance. Let it put on some green top
      My post on ground elder probably explains more about the strategy against this type of weed.

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  16. Thanks for the reply Roger, I wasn't sure if I was to spray it every few weeks or months ect. I'll have a read of you post about ground elder just now.
    Thanks again, adam.

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  17. Excellent post, Roger. Today a garden designer friend called me after seeing a photo my husband posted to Facebook of me attacking the garden of our new home. Somewhat apologetically she delivered the bad news that what I was hacking and throwing onto a heap was JKW. When I told my husband he said he felt physically sick and that we'd made a mistake. I can't tell you how grateful I am for your post. Like you, my thought is "it's just a plant". Anyway, I'm now relishing taking on this battle, and am somewhat relieved that it seems to be fairly confined to a couple of clumps (which had previously been treated I now realise) and enjoyed a hot summer. My question is, am I ok to burn what I've felled and also, shall I now just wait until spring to spray? Or should I give it the gift of glyphosate now? Many thanks, Roger. Truly appreciate the time you've spent writing all this. Emma

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    1. IIt sounds as if I made your day Emma!
      Only if the weed has made meaningful new growth and is still green should you spray now. If so it will be worthwhile
      Burning is the best way to dispose of any roots you might have dug out.
      Although tops are capable of rerooting if you keep an eye on them they can even go on the compost heap!

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  18. Thanks, Roger! Yes, you made my day. It wasn't the sort of thing we were expecting to discover at our new house. Your straightforward piece was an antidote to all the doom and drama I'd read elsewhere. I'll get spraying asap :)

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  19. Roger - great article. I note you've wondered about the effectiveness of the injection technique, and might like to know of my own experience.

    We live near rail property from which a HUGE bush (8 feet tall and wide) overshadowed our garden. After a bit of research I decided on drastic action - cut through the stems about 2 feet up (they were 2cms in diameter) and literally poured glyphosate down the tube.

    That was a single treatment 3 years ago. I've never sprayed it, but there's been no sign of life from that bush since.

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    1. Great to have your thumbs up Anon!
      I suspect your 'neat' glyphosate (if the amateur version) would be the same as my declared strength for Peter's successful injection as 1 in 5 commercial product
      ... on second reading your comment does not say you used it neat
      I would appreciate if you would confirm the strength you used

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  20. Unknown3 March 2017 at 19:09
    This is such a great page! I am a structural engineer and am well aware of the scare stories about structural damage and the large bills for getting specialists in to eradicate it. We have even had some of these specialists in to do 'CPD' sessions. There are also a lot of scare stories about property values plummeting or sales falling through because of it. It is good to see someone giving advice in a calm and sensible manner.
    I moved house a year ago and in the summer I noticed that the garden backing onto mine has knotweed growing in it (I sent a photo to 'ID my weed' via the PBA website and they confirmed it). I went around to their house to tell them about it (invasive weed/structural damage etc) and they just thought I was mad and told me to go away! It was not very tall (1ft) but it had spread wide. The leaves have died back now but I am sure it will spring back in the summer and I am just anxious to see how large it will be. As a new homeowner I am worried about my rather large investment going to pot!
    It is going to be difficult to have more conversations with them and get them to deal with it so I am wondering if I can at least keep it at bay by sticking a sprayer over the fence to get at the perimeter of the growth and at least stop it spreading my way! Do you think this is at all feasible? I just don’t want the rhizomes spreading under the fence line. Would it be illegal for me to spray nasty chemicals onto someone else’s property?

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    1. Thanks for the challenging question Louise!
      It is definitely a problem when noxious perennial weed keeps returning from a neighbour.
      Personally I have never resisted spraying right up to the border of a clients property (or my own). Most none gardeners either don't notice or are even grateful for any translocation-killed weed on their edge. Of course I am on dodgy ground if the neighbour wants to cause trouble or has prejudices against chemicals.
      It would be quite illegal to spray over the fence! Most neighbours if asked welcome help but that does not appear to be so in your case
      It might be desirable to go for a quick kill of your own knotweed. Peter Williams injection technique killed his daughter’s weed in one go. It never returned.
      A blog correspondent recently reported using nearly neat glyphosate sprayed on the cut back hollow stems of his knotweed with a claimed complete success. He let the fluid drain down into the stems.
      Killing this way avoids unsightly dying back and might advertise your activities less!

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  21. Hi Roger,

    Your article is great - it is so hard to find a rational, unbiased opinion on JKW - so thank you for writing one. We are in the process of buying a property, and there is a fairly extensive JKW problem - 4 large patches in different areas of the land, probably totalling about 0.5 acres total area (they are not too close to the house - 2 patches are near to each other in the middle of a paddock, and the other patch is running along a dry ditch, with the closest shoots being within maybe 15m of the house). We really love the property, and would still like to go ahead (we are probably crazy). We are keen to start treating ASAP however - so would it be wrong to treat the more mature shoots fairly soon (some are already a metre tall), and then if we were to treat 3-4 times, what other times would you recommend treating - we are happy to be in it for the long haul! Any advice would be hugely appreciated.

    Many thanks
    Sarah

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    1. You will be rid of it in three years so as long as you are not selling the house before them....
      For half an acre invest in a decent knapsack sprayer such as the Berthoud I have recommended elsewhere. Also get five litres of professional glyphosate.An amateur friend recently bought a gallon of Gallup 360 on the net for about 40 pounds.
      I am getting bolder in my strengths and suggest dilution of 1 in 40 for JKW.o a day when it is not going rain.
      I would wait another ten days before spraying your metre high weed. Let it expend a bit more energy in its rapid growth at this time of the year.
      It should not be necessary to spray the yellow dying shrivelled weed again, Just the new growth which will surely come in the form of new shoots or extended tops. You will know when it is about a foot high.Expect to spray two three times this season.
      Growth next year will be much dwarfer but will keep coming back. Spray at about a foot.

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    2. Thank you so much Roger, really appreciate the advice - have a great Easter!

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  22. Please don't be fooled by this sneaky weed. I had about a quarter acre of the ten feet high variety which I am still treating ten years later, but I also had a small patch on the bank of a stream which after two years had gone - or so I thought. Two years ago it came back, after an absence of SIX years! I hope I live long enough to actually see it off.

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    1. Thanks for the warnings Tony.
      I cannot believe it disappeared for more than a year.and came back. But as you say it's sneaky and low level infection might go unnoticed and build up again.
      Although Worsbrough cemetery took me nearly ten years there has been no sign of it for five years now.

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  23. Dear Roger, Many thanks for this page and all the information I was able to view. I found KKW in my back garden and there isnt a big patch but around 19 individual stems. Both of my neighbours either side have JKW in their gardens though. I treated it last year with weedkiller and it dies but it came back this year in new places.

    I was not aware that it spread itself and thought that it only spread if disturbed.

    I have treated it again last week with a good spray and a week later, most of the leaves and stems are folding over. I understand from the information above that you should only spray it 3/4 in the season, so my next spray should be in June.

    What happens if I spray it more that what was suggested? I am hoping that by next season it will start to die.

    My neighbours have been chopping theirs down not knowing it spreads more. I have made them aware, hopefully they can start treatment too.

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    1. Go by the new growth rather than the calendar - let it get say six inches before you spray.
      If you spray too often on either dying top or very small shoots you are wasting your money
      Anyone spraying larger areas too often might run up against legal annual maximums and be technically breaking the law
      I am increasingly impressed by results when people cut them back and really douse the hollow stumps with very strong glyphosate. I am not sufficiently confident to promote that method but recently have had spectacular results with dousing cut back ornamental equisetum that was starting to get out of hand in my cemetery garden

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    2. PS see comment from anonymous on 30 jan 2017

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    3. Thanks for that. Good luck and keep up the good work.

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