Japanese Knotweed

[svenrufus]

Japanese Knotweed is dieing off. I was surveying a site in Essex last month - a 'wasteland', rank grass, and tall ruderal vegetation, you know the sort of thing, found in any forgotten scrap of land anywhere you go.

In terms of botany, the most notable species there was Japanese Knotweed. There were maybe 4-5 distinct patches of it. What really struck me though was that one of these patches seemed to have completely died off.

It was definitely still the right time for them in that area, as the other patches were irritatingly vigourous and robust, but this one patch was just a collection of dead stems, no sign of any more stems growing up from beneath, and from what I could make out, it looked like the dead stems there were last years growth. The patch was about 3x4m in size, but a bit thin, so there was still other stuff growing beneath it.

I had never been to the site before, don't know the area well, but as far as I know there has been no work such as weedkilling going on there. It appears that this clump just died back all of its own accord. Most obliging.

So, the point of posting this here, is to ask - has anyone else noticed anything similar happen? If so, when, what sort of conditions, what sort of habitat, what was growing near it, how big was the clump that had died etc etc. Basically, I am interested to know if there is any common theme for this happening that might give a lead to a potential Achilles Heel.

I have often wondered if there may be a native plant that can out compete it. Maybe something as commonplace as our humble Bramble, which if it can be left to dispatch it on its own, leaves us with a much simpler job of clearing up afterwards. Anyone aware of any research that addresses that?

Cheers
Sven

[Gill Catton]

Originally Posted by svenrufus

Hi there
I was surveying a site in Essex last month - a 'wasteland', rank grass, and tall ruderal vegetation, you know the sort of thing, found in any forgotten scrap of land anywhere you go.

In terms of botany, the most notable species there was Japanese Knotweed. There were maybe 4-5 distinct patches of it. What really struck me though was that one of these patches seemed to have completely died off.

It was definitely still the right time for them in that area, as the other patches were irritatingly vigourous and robust, but this one patch was just a collection of dead stems, no sign of any more stems growing up from beneath, and from what I could make out, it looked like the dead stems there were last years growth. The patch was about 3x4m in size, but a bit thin, so there was still other stuff growing beneath it.

I had never been to the site before, don't know the area well, but as far as I know there has been no work such as weedkilling going on there. It appears that this clump just died back all of its own accord. Most obliging.

So, the point of posting this here, is to ask - has anyone else noticed anything similar happen? If so, when, what sort of conditions, what sort of habitat, what was growing near it, how big was the clump that had died etc etc. Basically, I am interested to know if there is any common theme for this happening that might give a lead to a potential Achilles Heel.

I have often wondered if there may be a native plant that can out compete it. Maybe something as commonplace as our humble Bramble, which if it can be left to dispatch it on its own, leaves us with a much simpler job of clearing up afterwards. Anyone aware of any research that addresses that?

Cheers
Sven

Very interesting, I'm afraid I'm not going to be much use to you because the only time I have seen what you describe there were stunted twisted specimens below illustrating that weedkiller had been used.
Perhaps that particular patch had grown into some particularly nasty contaminated land some way below the surface.

I wonder if bramble may struggle in competetion with JK as young plants would just be overshaded. Bramble in woodland always seems pretty wimpy when compared to specimens growing in more open glades only meters away....

[Dan Salter]

The patches on the land bordering our house show no signs of natural die back...granted they die back when sprayed with a herbicide giving you a short feeling of winning...then you turn your back and they have grown back...its a constant battle.

I KNOW the best method is injecting the stems but when there are thousands it just seems like an impossible and expensive task...Go away knotweed..JUST GO AWAY please.

[Chiltern Chris]

I'm unaware of anything that can compete with JK in this country but there is hope. I think Defra are on the verge of licensing field trials, starting next year of either a Japanese weevil or fungus both of which seem very effective at crippling JK and are completely species specific. I’ve not heard if they attack the JK hybrids. Out of all the major invasive species we have it looks like JK is the one which really can be brought under control over the next decade. I’m not in the Defra loop but I expect trials may start in north Cornwall and south Wales.

Chris

[svenrufus]

Originally Posted by Chiltern Chris

I'm unaware of anything that can compete with JK in this country but there is hope. I think Defra are on the verge of licensing field trials, starting next year of either a Japanese weevil or fungus both of which seem very effective at crippling JK and are completely species specific. I’ve not heard if they attack the JK hybrids. Out of all the major invasive species we have it looks like JK is the one which really can be brought under control over the next decade. I’m not in the Defra loop but I expect trials may start in north Cornwall and south Wales.

Chris

While I'd dearly love for there to be no more JK in the country, the thought of releasing anything into the wild to tackle it fills me with dread - surely we have to be able to learn sometime that we just can't be trusted to get it right! Species specific they may appear to be (at the moment), but once out there, who knows what they will end up doing.
Our history is littered with well intentioned cock-ups. I

[Dan Salter]

Originally Posted by svenrufus

While I'd dearly love for there to be no more JK in the country, the thought of releasing anything into the wild to tackle it fills me with dread - surely we have to be able to learn sometime that we just can't be trusted to get it right! Species specific they may appear to be (at the moment), but once out there, who knows what they will end up doing.
Our history is littered with well intentioned cock-ups. I

Yes i agree with this too and it worries me stupid...two wrongs cant ever make a right...introducing an non native to control an intorduced non native...

Didnt this happen with snails?...they introduced one to kill another type but they just ended up killing all the natives too.

[Chiltern Chris]

I agree, it’s a bit scary releasing non-native species, especially a fungus. I know they’ve been testing the JK pests for a few years in a lab and the science looks pretty watertight regarding prey species, adaptation ability and cross-breeding etc – but as they said in Jurassic Park, “nature finds a way”. I expect Defra are pretty jittery about the subject and will be cautious but nothing is 100% guaranteed when it comes to nature. If they do go ahead with field trials I’ll let you know.

Chris

[Phil Rusted]

Originally Posted by Dan Salter

The patches on the land bordering our house show no signs of natural die back...granted they die back when sprayed with a herbicide giving you a short feeling of winning...then you turn your back and they have grown back...its a constant battle.

I KNOW the best method is injecting the stems but when there are thousands it just seems like an impossible and expensive task...Go away knotweed..JUST GO AWAY please.

In what way exactly is stem injection the answer?? - Lack of research, vast amounts of chemicals, poor results.......
Would love to hear the reasons behind stem injection

[Hobjob]

Originally Posted by Chiltern Chris

I agree, it’s a bit scary releasing non-native species, especially a fungus. I know they’ve been testing the JK pests for a few years in a lab and the science looks pretty watertight regarding prey species, adaptation ability and cross-breeding etc – but as they said in Jurassic Park, “nature finds a way”. I expect Defra are pretty jittery about the subject and will be cautious but nothing is 100% guaranteed when it comes to nature. If they do go ahead with field trials I’ll let you know.

Chris

Its right to be a bit worried, but it is not all failures on the introduction
of species specific pests. South Africa has largely controlled
prickly pear which used to be rampant, with a specific beetle.

... and if you think we have problems with introductions, then read
up on the eucolyps introduced in SA

[Dan Salter]

Originally Posted by Phil Rusted

In what way exactly is stem injection the answer?? - Lack of research, vast amounts of chemicals, poor results.......
Would love to hear the reasons behind stem injection

I have been looking into methods of erradication...spraying doesnt seem to work to well, cutting just spreads the issue as new plants can grow from 1 gram of green stem, and by the root systems so digging out is not an option...burning doesnt work...so they say that injecting the herbicide into each stem then lets the poison sink down into the root system below ground.

And yes im with you....i dont like chemicals, herbicides, pesticides as much as the next person and if there was a natural way (which there isnt) of getting rid of it then great. We have a large wooden cabin /garage directly next to the JK and its only a matter of time before the foundations collapse and the JK fills the building....they can do a lot of damage and can penetrate through concrete and building footings. Hence why its such a problem on building sites ( which i quite like the way its slowing down the spread of building developement) but our house is a few hundred years old

[almostnormal]

the alternative is to chop it down and then pour the nasty round up down the tubes. has a similar effect as stem injection. EA have a booklet about controlling the stuff.

my understanding on the field trials is that the fungi/beetles are species specific, ie they only attack japanese knotweed if this is the case it could be a cheaper and more environmentally friendly solution to masses of round up.

[Paul mabbott]

Couldn't resist resurrecting this thread. Something I've not seen before, and I thought I'd seen F.j. almost everywhere: Hutcliffe Wood Cemetery, Sheffield - it seems to prosper on the graves ...

[Dan Salter]

Originally Posted by almostnormal

the alternative is to chop it down and then pour the nasty round up down the tubes. has a similar effect as stem injection. EA have a booklet about controlling the stuff.

my understanding on the field trials is that the fungi/beetles are species specific, ie they only attack japanese knotweed if this is the case it could be a cheaper and more environmentally friendly solution to masses of round up.

I see your point Almost...but the worry is they have said this about introduced control methods in the past...and when they start killing other things they go " Ooops...we were sure it only liked Jap Knotweed".

[oceanroc]

I have a cure... Take 4 boys from an EBD school with lots of energy and anger to spare, let them find sticks, and tell them to knock down the knotweed. Then walk away and leave for 15 minutes. You will hear lots of noise and return later to find flattened area and (if you are lucky) boys still alive and rather more limp.

Then return to work and be reprimanded because the JK spores could be spread by contact with the boys' clothing.

I know of no cure. Perhaps bracken??? IT seems to be able to establish a monoculture in most places once established.

Oceanroc

[bee warrior]

I dont think JK spreads by spores?
It is spreads vegetatively by rhizomes as I believe it is not known to produce seed in this country. However the smallest fragment can root and grow and this is why it is so easily spread by human activities. Anyone removing JK has Duty of Care to ensure it is disposed of safely. Best practice would be on site, piled up and regularly checked to ensure it is dying off and not rerooting. If removed off site it needs to go to a landfill that is specifically able to deal with JK in accordance with the law.