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Continental touring and Japanese Knotweed

Posted: 15 Jun 2016, 8:52pm
by steady eddy
I noticed last week in Holland that there are many outbreaks of Japanese Knotweed growing alongside stretches of the north sea cycle route. Two big patches just south of the Hague particularly spring to mind as they hung over the cycle path. I have seen it else where in Germany alongside the Rhine. It spreads particularly well along transport corridors and can regenerate from small fragments of root or leaf. It is not something you want in your garden and you can now be fined in the UK for not controlling its spread. It is resistant to most weed killers and can grow through concrete. If you have an outbreak and want to remove you can't just cut it down and compost it. It needs expert treatment or digging out in a controlled way and carting to a special waste disposal site.

It may seem pedantic but It seemed prudent on returning home to hose the bikes down well away from the garden to reduce the risk of spread. For those of you not familiar with this plant and touring on the continent it would be worth looking at the many websites where it is detailed so that you are familiar with its leaves at least.

Lots of Giant Hog Weed as well growing by the dikes. This can produce very serious skin burns if touched. it is not a common site in the UK. Being aware of what it looks like could be a life saver.

Re: Continental touring and Japanese Knotweed

Posted: 15 Jun 2016, 9:04pm
by Paulatic
I had some on my building plot when I bought it. It had come from a patch of it the other side if the railway line. Network rail certainly killed their lump off with something. I used 2 4D neat on the leaves had to do it 2x in first year. Year 2 no sign of it Year 3 it came back so I treated it same way again and it's never been seen again.

Continental touring and Japanese Knotweed

Posted: 15 Jun 2016, 9:30pm
by Heltor Chasca
Note the exemption: It can be burned on site (JKW) so you can avoid the usual administrative palaver and expense. HOWEVER if you cause any further spread due to carelessness that's when you can incur trouble. It cannot be moved off site.

That said: I personally think it is demonised beyond all reason. Propaganda? It's relatively easy to control organically and I have NEVER seen it causing any environmental harm. Round here there are a few large swathes and it's a simple as that. Large swathes that cause no further harm. In fact it supports a decent number of inverts. 2 of my gardens have it and it's no issue. It's very pretty too. Ground elder and bind weed. Now those are two baskets I dislike. and cow parsley. Just a little bit

There are much more problematic plants. Some grown commercially. I'm hinting at monoculture without starting a fierce debate

EDIT Giant hogweed is more common than you would think especially here in the SW. One of my client's SILs has horrific scarring all over his torso. From strimming back vegetation in Wales WITHOUT a shirt on .

Come in Ben Forest.

Re: Continental touring and Japanese Knotweed

Posted: 15 Jun 2016, 10:35pm
by gaz
I'm OK with identifying JKW as I pass some on my commute. GHW I find hard to distinguish from just plain Hog Weed. GHW cuttings are also in the controlled waste category.

Re: Continental touring and Japanese Knotweed

Posted: 16 Jun 2016, 9:39am
by pwa
Heltor Chasca wrote:Note the exemption: It can be burned on site (JKW) so you can avoid the usual administrative palaver and expense. HOWEVER if you cause any further spread due to carelessness that's when you can incur trouble. It cannot be moved off site.

That said: I personally think it is demonised beyond all reason. Propaganda? It's relatively easy to control organically and I have NEVER seen it causing any environmental harm. Round here there are a few large swathes and it's a simple as that. Large swathes that cause no further harm. In fact it supports a decent number of inverts. 2 of my gardens have it and it's no issue. It's very pretty too. Ground elder and bind weed. Now those are two baskets I dislike. and cow parsley. Just a little bit

There are much more problematic plants. Some grown commercially. I'm hinting at monoculture without starting a fierce debate

EDIT Giant hogweed is more common than you would think especially here in the SW. One of my client's SILs has horrific scarring all over his torso. From strimming back vegetation in Wales WITHOUT a shirt on .

Come in Ben Forest.


Sorry to disagree but JK certainly does cause serious environmental harm. It can gradually replace woodland by shading out saplings, so that when the older trees die off there is no new generation to replace them. it also shades out native ground flora. You can end up with a rich and varied woodland being replaced by a JK blanket with very little of anything else. In the valleys of South Wales it dominates many hectares of land. It is a huge problem for those who, like myself, have been involved in trying to improve woodland for wildlife diversity.

I've succeeded in killing off areas of up to several hundred square metres using a combination of glyphosate (several applications) and matting. Basically, there are geotextiles that knotweed struggles to punch through. Flatten the area, cover with matting and weight it down with something (gravel, wood chips, whatever) and most of the JK will be killed, Eventually. You should be ready to leave it like that for a year or more. It will still come up around the edges, and anywhere the mat has been damaged, and that is where the glyphosate comes in. But because you have reduced the scale of the problem, the area to be treated is much more manageable and less chemical is needed. Hit the plant before it gets too tall. I feel that the soft, young leaves are best at taking the glyphosate in. But another good time to hit it is as it flowers, just before the leaves fade. The theory is that as the plant withdraws nutrients to the roots in late summer / autumn, any glyphosate in its system will be taken down to the roots to finish the job.

Glyphosate should be used with care because it will kill any leafy plant you get it on. Be careful where you spray and don't try it on windy days. Keep it out of streams and don't get it all over yourself. Or your neighbours. Stick to the recommended dose. Compared to many herbicides, however, it is fairly safe and is thought to leave no long term nasty residues.

Re: Continental touring and Japanese Knotweed

Posted: 16 Jun 2016, 12:03pm
by iviehoff
From a gardening perspective, the very worst weed to get rid of is a native: horsetail, Equisetum spp. It has roots about 5m deep and basically don't expect to be able to get rid of it. It can resprout after being concreted over for decades. Fortunately if you haven't already got it, it doesn't travel around and establish itself to the extent of the more mobile monsters; it's not commonly found in gardens.

I think it is unlikely that cyclists will be spreading JKW. Lorries are more often implicated. Although it can spread from "small" pieces, the canes are quite thick and in practice and it would be difficult to break a piece off by hitting it with your bicycle, and also you are going to notice if a piece of JKW of sufficient size to spread has got stuck in your wheel. In any case, it is so common in Britain itself, that a week in the Netherlands makes no practical difference to the risk. I would imagine the JKW spread onto segregated cycle paths in NL is more likely due to maintenance vehicles, eg for vegetation clearance.

We had Giant Hogweed Hysteria in our village recently, and had warnings sent from the school that it had been spotted locally. Eventually I found out where the alleged sighting was, and I went there and discovered it was innocuous common hogweed, which can also grow 10ft tall, but does not have the enormous leaves and general solidity of GH. It tends to be plant you find alongside ditches which are permanently wet, and we don't really have such conditions in our village.

There are several kinds of invasive giant hogweeds, and they tend to be invasive in different parts of Europe. Here and in W Europe generally north to Denmark and east to Germany, we have Heracleum mantegazzianum, which is a nasty. In Sweden, Norway and Finland, right up to the arctic, the giant hogweed there is Persian hogweed, which I think is relatively innocuous. In Poland and NE Europe, they have Sosnowsky's hogweed, which is also a nasty one.

Re: Continental touring and Japanese Knotweed

Posted: 16 Jun 2016, 12:16pm
by pwa
I've heard that horsetail can be killed off by glyphosate, but only after whipping the stems with a cane to damage the surface to allow the systemic weedkiller in. I don't know if it works.

Other (organic) methods of dealing with it must include shading it out with dense shrubs that are simply taller.

Re: Continental touring and Japanese Knotweed

Posted: 16 Jun 2016, 1:39pm
by Heltor Chasca
Horsetail is a dinosaur amongst plants. It's ability to shield itself from chemicals and regenerate after any organic method is impressive. The clue is in the name (silica) I'm lucky I that I don't come across it in my gardens much.

No wonder it's still about. Nothing will conquer it.

Re: Continental touring and Japanese Knotweed

Posted: 16 Jun 2016, 3:12pm
by pwa
Heltor Chasca wrote:Horsetail is a dinosaur amongst plants. It's ability to shield itself from chemicals and regenerate after any organic method is impressive. The clue is in the name (silica) I'm lucky I that I don't come across it in my gardens much.

No wonder it's still about. Nothing will conquer it.


One of those nuisance plants you have to admire.

Re: Continental touring and Japanese Knotweed

Posted: 16 Jun 2016, 3:28pm
by Neilo
Heltor Chasca wrote:Horsetail is a dinosaur amongst plants. It's ability to shield itself from chemicals and regenerate after any organic method is impressive. The clue is in the name (silica) I'm lucky I that I don't come across it in my gardens much.

No wonder it's still about. Nothing will conquer it.


Had to kill the whole garden when I neglected it when I had horsetail.

JKW in most of the valley where I live, It seems to follow the rivers

Re: Continental touring and Japanese Knotweed

Posted: 16 Jun 2016, 4:21pm
by cc1085
Horsetail can be used to prevent potato blight, but you must know what you are doing. I wouldn't worry about any plants/vegetation/shrubs/trees etc. Remember all flora is poisonous. Looks like Glyphosate use will be banned in the near future as a probable carcinogen. Any way how did I get into this, I came on here to ask about recumbent v diamond frame. Which is easier to travel on? speed is not a consideration.

Re: Continental touring and Japanese Knotweed

Posted: 17 Jun 2016, 2:22am
by PJ520
Bit of off topic trivia here. The UK's beloved European or Common Privet is a noxious alien species in the Virginia. So it's not just them invading us.

Re: Continental touring and Japanese Knotweed

Posted: 17 Jun 2016, 10:11am
by PDQ Mobile
In the upper reaches of the Moselle river in France around Remiremont JK has overun huge areas of the river bank- mile after mile of it.
It suppresses almost all other vegetation and affects the rivers ability to flow and flood. It has blighted the place.
It is an enormous and very (and I mean very!) expensive and intractable problem.
Best got rid of at first sight.

Re: Continental touring and Japanese Knotweed

Posted: 17 Jun 2016, 11:41am
by iviehoff
Cows like to eat it. This can be a useful way of keeping it under control in some situations.

Re: Continental touring and Japanese Knotweed

Posted: 17 Jun 2016, 11:49am
by pwa
I've heard that in the UK, Japanese Knotweed was first recognised as a problem in the wild in the Llynfi Valley of South Wales (Maesteg area), and it is certainly very well established there. It does tend to exclude other plants, including tree saplings. I've never noticed it being a significant food source for any creature.