Japanese Knotweed - a growing problem

[diggernotdreamer]

Just wondering has anyone any personal experience or knows of anyone who has successfully managed to kill a stand of Japanese Knotweed. I have volunteered to do a presentation to make people in our village more aware of the problem. Some houses here have it up to the back door and have no idea what it is. Having been an avid knotweed spotter for the last 20 years (yeah I know a bit sad and anoraky), I have watched its progress and know that there are a lot of programmes in the UK to deal with it. I don't know of any organic approaches as it is quite difficult to tackle. The council here only became aware of it two years ago

[Flo]

Apparently the flower heads have to be bagged up before they seed and taken to be disposed of by licenced operatives to prevent the seeds propogating - which they do very easily of course, being from a sturdy weed.

Clearing the leaves and stems of Japanese knotweed that are above ground and then removing soil contaminated with roots, rhizomes (underground root-like stems) and seeds can provide faster results than just spraying with herbicide and will be as organic as you can get but it's a game on to dig all the stuff out and then you have to dispose of the results which again will be your licenced operative - not stuff to compost, it doesn't. Any soil left behind will most likely have seeds in it so you could be on a long term job to get rid of the stuff going down this route. Suppose that a prompt bonfire would ensure complete destruction (if you can arrange bonfires of course without upsetting all the neighbours) and it would need to be done promptly before the roots take off and start the cycle again (if you are in a smoke free area, forget bonfires).

I've heard that a very strong dose of Glyphosate down the resulting hollow stems after removing heads does wonders for killing the plant but due to the extensive root system you can be doing this for two or three years and should really have a proper certificate so that you have access to stronger than garden centre watered down roundup wee. Such fun. Having been the holder of appropriate certificates in the past for a lot of wonderful sprays (many now banned), that comes from some long ago training. Never had to deal with the stuff. Now talk to me of mares tail and Himalayan Balsam and I can be quite up to date on those two.

[ojay54]

if you've got a holding number(if you haven't then get your friendly local smallholder(!) to do this for you) go to your local Agri supplies outlet,and buy full strength Glyphosate.Then ,as you say,cut the largest stems about 2' high and mix the stuff with 10%water(just to make it easier to pour) and pour it down the hollow stems.
Severe infestations you will have to repeat this 2X a year for maybe 2 or 3 years.
I don't like chemicals,but don't kid yourself that anything else will treat a bad infestation.A friend of mine ,once an ordinary industrial landscaper,now does this stuff full-time ,mostly in the West country and South Wales,gives you an idea of how bad it's become.

[Zech]

I've heard (possibly from Andy) that it's possible to eat it to death, but you have to harvest every shoot for five or more years.

[diggernotdreamer]

Thanks for the replies.

Thankfully, Japanese Knotweed does not spread by seed, only female specimens were sold. Seed produced will not be viable, thankfully. There are other knotweeds, Bohemian and giant which are more unusual, but have the potential to produce viable seeds and could produce hybrids.

Although not a notifiable weed, it is illegal to grow or it encourage it to grow. Once the stems or rhizomes have been cut or excavated, it is then considered hazardous waste and has to be dealt with accordingly. Removal off site is an expensive option and any plant material (all parts of this plant can propagate) has to be dealt with in a responsible manner. Deep burial on site of soil and rhizomes in a sealed membrane in a pit at least 3-5 metres deep, Stems must be dried of the ground on a sheet to prevent contact with the ground and when dried burnt to ash, no pieces can remain. Boots must be cleaned off before leaving the site as must any vehicles and machinery. Common vectors for the spread are hedge cutting and river erosion. When dealing with the weed on rivers, care must be taken when using herbicide and often wiping and stem injection are indicated rather than spraying.

I do not have knotweed on my land happily, but I do have Himalayan Balsam, which I am on the cusp of eradicating over the last six years, it is down to just a few plants popping up here and there, but local beekeepers keep chucking the seed around up the mountain near here as they like it as a nectar plant.

[boboff]

We get it here along the River bank.

The Cornish spray it with Glysophate some years, the Devonians arn't that bothered with it, they both hate Giant Hogweed, which are sprayed yearly and neither care about Himalayan Balasam.

I can see a Big Stand of JK out my window now, Devon side, the top 4 foot has turned a lovely yellow, pretty.

[ina]

I've heard (possibly from Andy) that it's possible to eat it to death

Whose death...?

[MKG]

True - he has a recipe for JK wine.

Hopefully it doesn't make a very nice wine, otherwise I can see winemakers keeping a surreptitious plantation of the stuff.

[doofaloofa]

I have experiance fighting knot weed and have been quite successfull

The key is to be persistent and cut regularly, once a week or more

idealy start as soon as they show themselves in spring

Patience is also required as this method may take several seasons

Turning the infested area into lawn and keeping it well cut is effective

it is important to familiarize yourself with all the growing sites and keep at them

Cuttings can be fed to rabbits, dried and composted or just left to rot, as any regrowth will be caught on the next cut

Digging up roots is also effective, though more labourious

[diggernotdreamer]

Thanks Doofa. How successful have you been, ie have you got rid of it, have you reduced the size of the stand and how long have you been at it. This may be ok for a stand say in a garden, but if you have it in lots of places and say the size of an acre covered it might be more tricky defoliating. Not sure I would ever risk composting it, I would dry it and then burn, it burns very hot so might be useful biomass in a stove. The roots extend 7m diameter and can go down 3 meters or more which is why it takes so long to deal with it. I don't want to be doom and gloom, I would like a few success stories.

[doofaloofa]

I have been most successful where I was most persistant. I tend to pull it whenever i see the shoots. Where our whole lawn is now was thick with it. The constant cutting of lawn maintainance won the day, any bits that turned up in beds were easy enough to issolate and erradicate

Apperently if you can pull it whist it is still red you sap the roots more than if it is green and therefore producing its own energy

Larger areas could be maintained with machinery, like a tractor mower?

The places I have seen it get out of hand are areas that are neglected or difficult to get at

[doofaloofa]

[doofaloofa]

a weeks growth

[doofaloofa]

a large clump in heavy woodland killed in a couple of yers by cut and cut again method

[doofaloofa]

hiding in amongst other plants

Sneaky!