Japanese knotweed

It is evil. We have a relatively small but spreading infestation and are bordered by a bad infestation. The first new shoots have just started appearing. I am already familiar with its useful properties - we do eat new shoots, and we collect dried stalks for (very good) kindling. but I need to eradicate it. We have had a consultation with two companies, one of which is the one used by the national park (our property is within the park, but we dont have to use them), both said that due to the specifics of the site, they would not recommend mechanical methods (digging) and would treat it with chemicals. I am keen to avoid this if at all possible, not least as we are just a few hundred meters upstream of the reservoir we get our drinking water from! (the knotweed is along the river banks). I have thick black plastic sheeting that I will be putting down tomorrow over as much of the affected area as possible in an attempt to starve it of light (I can leave the plastic there for years if necessary, it's an area that won't be used for anything else).
Are there any other ways to treat it? If I do have to resort to herbicides, are any of them less evil than others, or are there any means of application I could use to limit impact on other plants and the wider ecosystem?

A couple of times I have accidentally eradicated something that is said to be impossible to eradicate, just by harvesting it a lot and pulling it up when I could. If possible, try conventional pulling up again and again, especially at whatever time is best for weakening it, probably right after flowering and before setting seed. It's time consuming but if you have the time and can enjoy, give it a try.

I would put something else heavy over the plastic....to prevent the spears from punching through. Old scraps of carpet come in handy for this. Being a tall, rather than a creeping, perennial, it also seems that simply regularly cutting or mowing it would eventually starve it out, but it might take a couple of years.
Then there's the idea of penning animals in there with it....goats, pigs, even chickens. Of course you'll have to supplement their food, but by having them in there where the weeds will be about the only fresh stuff will motivate them to munch it. And pigs will dig, too...

Thanks for your reply. That is a really good point on the carpet actually, I will try to get some on it this week.

I have considered animals, but the patch on our land borders the river - right up to the water's edge - so it's not really practical.

I will try digging as well, because there are a few areas that I couldn't cover with plastic. But the rhizome of each plant can go down 2 meters and horizontal 7 meters (I have seen this myself so it's not hyperbole)!!! And as the plant can regrow from 1 sq cm of rhizome or less, I am very nervous about attempting to dig it out, and possibly making it worse - also it is a criminal offense to 'cause the plant to grow in the wild' where we are, as it's such a detrimental species.

I'm sure you probably are already aware but the environment agency website has useful guidance for dealing with invasive, see link below:

http://www.environment-agency.gov.uk/static/documents/Leisure/Knotweed_CoP.pdf

Hope this helps and good luck!

S Carreg : I have it on three sides of me, and it has also invaded the nicely composed pile of horse manure i used to have free access to. I have
observed that very small pieces of the roots have the ability to propagate. thats the bad news, the good news is a neighbor of mine eradicated it by
covering the entire ground where he had his infestation, with two layers of black plastic (after first removing a few trees that were providing over-
head cover/shading.

After two years he took up the black plastic. Then later on he terraced the slope that had been contaminated/infested and replaced the black plastic
on top of the terrace running the two layers under the pressure treated lumber that made up his cribbing/retaining wall, and then put pea gravel
down everywhere on the terraced slope, The gravel was there because he not only wanted to get rid of the knotweed, he wanted to not have to mow
this area, while this does sound less then ideal, it is the area behind his house where people gathered - there was a micro climate effect that made
the prime time to be there the late afternoon rely evening.

I just walked across the road and where there was enough gravel over the plastic it seems to be holding up well!

Be safe, keep warm, PYROMAGICLY Big Al


P.S. Could any one help me get rid of some mint !

S Carreg: Japanese knotweed is indeed a menace in Wales. Have you talked to Martin Bryant at Environet UK yet?
He's based in Wales and all he does is eradicate JK so may be worth a chat. 029 2060 1863
Allen Lumley may well have found a way to contain his infestation, but I'm afraid there's no way he's killed it! It will perhaps be dormant for now, but it will reemerge in the fullness of time
in its insatiable quest for water and light.

I may not have made myself clear the two layers of black plastic burned up all of the surface plants and sterilized the ground,
and kept it too dry for any thing to grow.

It seems that two layers of plastic is the secret to getting the ground hot enough, the second layer of plastic helps hold the heat in

Be Safe, keep Warm, Pyromagically - Big Al

Thanks for further replies. I will definitely contact Martin Bryant, thank you for that.

Yesterday our local national park ranger came down for a chat and to look at the infestation. The potential good news is that there might be some community money available to treat the infestation as a whole - tracing it back to the source further up the river and treating the whole thing. Because as several people have pointed out, there's little point in treating on our site if it's just going to keep washing down onto our land. Because the flows through an area under control of the forestry commission and the national park before it reaches us, there is a chance that this can be tackled as a group effort. I read through the environment agency guidance for property developers and unfortunately a lot of it does not apply to us - the mechanical methods of removing huge volumes of soil and sifting and berming it to treat the rhizomes are not an option because it borders the river (and because we can't afford it!). Some of the shoots are actually coming up in the water! This is also why attempting to 'burn' it by heating it up under the plastic is not an option - it's in the water table. And in any case we get nearly 2 meters of rain per year so 'dry' doesn't really figure into the equation!

I have Japanese Knotweed growing between the garages here in Toronto, ON. It is only ever a nuisance when it starts growing inside the garage, through the walls.

I realise that as the park is handling it now, it may be out of your hands, but I'd be asking yourself if the removal of the knotweed is worth poisoning the water with sprays. The only commercial sprays I can think of that may not be deathly toxic to humans rely on oversupplying the plants locally with excessive levels of something they absorb readily. I think I've heard of iron being used this way. Have you thought of making a tea (for garden application) of some local plant that exhibits allelopathy? If you have walnut trees, for instance, find out if any part of them can be boiled or whatever for its juglone, which should keep anything but walnut from growing in the area where it is applied (walnut and juglone were illustrative examples and may not actually apply to the eradication of Japanese Knotweed).

As to animal solutions, before you dismiss them, find out if goats will browse Japanese Knotweed. They are petrified of water, from what I understand, and so make perfect riparian area browsers. And last I checked, passing through the bowels of a goat will stop all but the hardiest seeds from sprouting.

In my books, spray=bad is something of a rule, and any kind of water in the equation makes the effect worse, not because it is worse for the user, but because it is constantly diluted, it needs to be constantly reapplied, or heavily dosed in the first place. I wouldn't poison where I live.

Why is Japanese Knotweed so bad that you'd want to kill yourself and your part of the world? Without generalising too much, I think this sort of situation and reasoning are a problem with the human treatment of natural space. We give pioneer plants horrible titles like "invasive" and "noxious" and then we poison and sterilise because we think we know best.

You know what could be done with your "invasive?" They are among the first pollinator plants to bloom where we are, and honeybees use it to make a honey very much like buckwheat (because it is a member of Polygonaceae). Not to mention the fact that with the number of predatory wasps it draws, I will never have a problem with certain types of fruit and veggie pests. Instead of killing the host (your ecosystem) with chemotherapy (the spray) to eradicate what you think is cancer (but is really just another plant), raise bees.

In all likelihood, the emergence of so many invasive species, apart from being the unintended fallout of shipping and transportation, are just the physical symptoms of climate change, in my opinion. If your environment becomes unsuitable for its native inhabitants, and a niche opens up, if an "invasive non-native," or a group of such, doesn't move in, it will remain empty, and whole food webs can die. We're just looking at species succession over time, and from a perspective so near that we can't even see when we're doing something stupid.

-CK

Why do I want to get rid of it? here are a few reasons: it can damage the house - it's an old stone house with no foundations and lime mortar and if the knotweed gets to it it could cause structural damage within a matter of weeks. because the knotweed can regrow from such tiny pieces, if a piece gets stuck in a shoe or something, I could be facing that situation at any time.
It is highly damaging to the environment here. It is not one of the earliest things to flower in this area, not by a very long way and while yes, honeybees do like it, I am planting and encouraging beneficial native plants for the bees.
As I am upriver from the reservoir, I also have to consider the implications of knotweed for that environment, which are bad. It is already damaging the flood defense bank that protects my property, and clogging the channel under the road, affecting the flow into the reservoir. The water company is concerned about structural damage to the dam as well.
It is shading out many native species of beneficial riparian and wetland plants - such as willow - which would protect the banks.
I hear what you are saying and believe me, chemical treatment is an absolute last resort - I have never before even considered the use of any chemical treatment in my gardening. But this goes beyond what I want for my little patch. KW is not simply a poor misunderstood coloniser, it's doing very appreciable active harm to the environment here. I'm very happy to work and live with things that many other people around here consider to be invasive and useless - dandelion, dock, thistle, you name it. But not something that is a recent introduction with catastrophic effects on both the human and natural wild environment. And while I take your point about the human race generally being piss-poor at 'knowing best', frankly I think it's irresponsible to let KW take over the watercourse and area.

I will definitely investigate the goat option more, as goats were always in our long-term plan anyway.

I advocate the "animals method" especially pigs, keep them hungry enough and they will dig for even the tiniest pieces! Granted, pigs+ riparian area = ecological bad idea, but to get rid of JK...

and at the end of the day you have all that nice "gass fed" pork!
or you could just sell them at the end of the season, not worth much but at least they'ed pay for themselves.

Okay, so in my above posts, I said it was one of the first pollen producers to bloom. That is inaccurate. I'm sorry. I was thinking of something else. But the bees do love it, and so do apiarists. But I'm sorry its a problem for you. I would just balance the potential damage caused by this invasive versus the damage to the water table and surrounding ecology if you need to knock it out chemically.

Just walk around once a week and knock the new shoots down. It will eventually deplete the plants' stored energy reserves, and no more knotweed. You'd have to go to the source, though, as in all cases, long-term.

Unless, as Tom suggests, you let the animals do the work...

-CK

allen lumley wrote: P.S. Could any one help me get rid of some mint !

Haha, mint was one of the things I accidentally eradicated once. I had planted it in a corner of the flower garden a few years earlier, and then decided it was too rampant, as it has spread into and among perennials. I had heard how hard it is to eradicate, so I thought if I just pulled up all that was visible and easy to get at, it would regrow only enough for our needs. So I spent a few minutes maybe an hour, crawling around under thorny roses, sure I couldn't get at it all. But not even a single shoot came back.

Rebecca Norman wrote:

allen lumley wrote: P.S. Could any one help me get rid of some mint !

Haha, mint was one of the things I accidentally eradicated once. I had planted it in a corner of the flower garden a few years earlier, and then decided it was too rampant, as it has spread into and among perennials. I had heard how hard it is to eradicate, so I thought if I just pulled up all that was visible and easy to get at, it would regrow only enough for our needs. So I spent a few minutes maybe an hour, crawling around under thorny roses, sure I couldn't get at it all. But not even a single shoot came back.

I did almost exactly the same thing! Now, I am begging some back from everyone I gave it too. I even mowed it thinking it would survive anything...not so.

I have not dealt with something as aggressive as japanese knotweed but I think by keeping 'last resort' chemical control on the table some more creative and long range effective solutions might go undiscovered.