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Japanese Knotweed - how to kill?

dryan

http://www.breakingnews.ie/ireland/residents-fear-for-homes-over-japanese-knotweed-infestation-794801.html

Started of with a small infestation 2 years ago in a beech hedge at the road entrance to the home place.
Was out trimming the hedge earlier in the week and i see thats its spreading at an alarming rate along the hedge on the site boundary.

Also starting to notice it in the farm boundary fences as well.

Is there any product out there that will kill it?

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Mousewar

Japenese knotweed in my estate is looking very poorly now. Starting to wilt and many of the leaves are browned. I fear my neighbour went at it too early. He seems buoyed by the results but I'm skeptical as I doubt it'll even be alive for the late september spray. He has been spraying it weekly since at least the start of August and says he will continue that up to the end of september after which he will spray monthly. Not sure what he imagines the point of that will be as it will be long dead. My next challenge will be to stop him spraying the new growth next spring.

Incidentally, my journey home on the dart every day shows me an increasing abundance of japanese warning signs along the dart line. I'm not sure if that indicates its spread or just that IE are taking it seriously at last.

my3cents

Mousewar wrote: »

Japenese knotweed in my estate is looking very poorly now. Starting to wilt and many of the leaves are browned. I fear my neighbour went at it too early. He seems buoyed by the results but I'm skeptical as I doubt it'll even be alive for the late september spray. He has been spraying it weekly since at least the start of August and says he will continue that up to the end of september after which he will spray monthly. Not sure what he imagines the point of that will be as it will be long dead. My next challenge will be to stop him spraying the new growth next spring.

Incidentally, my journey home on the dart every day shows me an increasing abundance of japanese warning signs along the dart line. I'm not sure if that indicates its spread or just that IE are taking it seriously at last.

I wouldn't worry too much if your neighbor kept pumping the the Roundup onto the JK while there was still good leaf to take it up he might have done a good job.

The fact he keeps spraying it has to be a good rather than a bad thing so if any does come back next year I'm sure he'll be back out on to it.

Now btw is a good as time as any to start spraying.

cosbawn

So now is a good time to spray? And again in about 3 weeks? I have that right? The weathers been very broken here ( north west ) for last two weeks and wondered what I was gonna do. But it’s been fine last two days and grass is nice and dry today so action stations tomorrow all going well.

orm0nd

cosbawn wrote: »

So now is a good time to spray? And again in about 3 weeks? I have that right? The weathers been very broken here ( north west ) for last two weeks and wondered what I was gonna do. But it’s been fine last two days and grass is nice and dry today so action stations tomorrow all going well.

no need for the second application , other than doing patches that were missed first time

Edit

the slower the kill gives the chemical an oppotunity to travel well into the root system where it is most effective for long term control

GreeBo

As others have said, you cant cut or pull it to kill it.

there is a central root ball that can be a couple of feet in size, the rhizomes/roots run like bamboo and can popup several metres from the root ball.

You can kill these runners easily enough with roundup applied at the right time, but unless you treat ALL the visible growth you are not impacting the root ball.

If you do treat all visible growth with roundabout (injecting) then you destroy the plants ability to gather energy for that growing season and so the plant uses some energy from the root ball (think if it as a fat store)

Next growing season you need to again treat the visible growth and again you will reduce the size of the root ball.

Repeat this process for 5-10 years and you should be done, but a single cm of plant is enough to start a whole new root ball that you wont be aware of until you have another infestation.

Simmental.

I sprayed Japanese Knotweed last Autumn and there is a few shoots coming up now. Do I let them grow and wait to spray again in the Autumn or should I spray the shoots as the come up now?

my3cents

Simmental. wrote: »

I sprayed Japanese Knotweed last Autumn and there is a few shoots coming up now. Do I let them grow and wait to spray again in the Autumn or should I spray the shoots as the come up now?

Personally I'd let them get to as high as possible while still leaving it easy to get over them with a spray. Say no more than a meter tall then spray.

The ideal method is to leave them till the Autumn but I prefer to be proactive and get this early spray in and another one in the Autumn.

Both are know documented methods.

Markcheese

There's a good side and a bad side to repeated spraying with roundup,
The good is you've a wasteland where you can easily see the knotweed shoots coming up, the bad is you've a wasteland.
If you can see individual shoots coming up, they could be "wiped " with a round up gel..
I think I'd give them a good dose as soon as there is visable leaf,
If youre not spraying it... It is edible... Break off the young spears or shoots as they come out of the ground.. And cook like asparagus...
Its not supposed to be great...

GreeBo

my3cents wrote: »

Personally I'd let them get to as high as possible while still leaving it easy to get over them with a spray. Say no more than a meter tall then spray.

The ideal method is to leave them till the Autumn but I prefer to be proactive and get this early spray in and another one in the Autumn.

Both are know documented methods.

The longer you leave it to grow the bigger the root ball is getting...they die by starvation of this root ball so i wouldn't be letting them go very long...

my3cents

GreeBo wrote: »

The longer you leave it to grow the bigger the root ball is getting...they die by starvation of this root ball so i wouldn't be letting them go very long...

No that isn't how it works.

It is well proven that the most effective time to spray JK with glyphosate is in the Autumn before it dies down. Monsanto themselves recommend spraying at flowering time which is the end of August. Only later in the year does the plant transport enough of the glyphosate back down to the root system to get a really good kill.

However the problem once the plants are fully grown is that they can be just too big to spray easily and to get good coverage. The answer is to time an earlier spray to reduce the growth so the plant is at a more suitable height to spray late in the growing season.

I have tried many spraying methods and chemicals against JK and always the best kill rate (never 100% but still good) has been with spraying with glyphosate after flowering. Its hard to be sure but I suspect that I've had a better end of year kill rate with glyphosate when I've sprayed in May when growth is at about a meter (the window to spray is small as the plant goes from 1m to 2m in a week) with triclopyr (SBK Brushwood Killer). I stick with glyphosate now as its cheaper.

Once you are really on top of the JK you'll probably start to get small plants growing back that are very small compared to the originals. Again these ideally should be sprayed late in the season.

Here is what Monsanto have to say https://www.monsanto-ag.co.uk/roundup/roundup-amenity/difficult-weeds/japanese-knotweed/ and these guys in Cornwall were some of the first to tackle JK as an invasive species in the UK https://www.cornwall.gov.uk/environment-and-planning/trees-hedges-and-woodland/invasive-plants/japanese-knotweed/guidance-for-control/herbicide-treatment-for-japanese-knotweed/ for many years they were the major source of JK control information on the web.

cosbawn

So my nice crop of JK took a good hammering from the spraying last year. I was actually able to get right in at it as opposed to this time last year when it was a bloody forest and I nearly broke my ankle tripping over stones. The stones are from a wall that the JK has pulled down. So I'm hoping this spray will curb the height as I reckon I got it just in time. So overall I am very pleased. I'm only sorry I didn't take a photo of it last year before I started

Mousewar

The knotweed in my estate has not returned this year so far. I thought my neighbour was making a mess of treating it - his spraying had it totally dead by the end of August so i feared the weedkiller would not have penetrated the roots much.
Still, looks like we don't have to worry about it this year. Expecting it to return next year though.

patsy_mccabe

Only today I noticed a big patch of dead JK near Limerick City beside a public road. Looks like the Council sprayed it.

6600

Would something like forefront not be better? Kill the weeds and leave the grass instead of bare ground for the JK to take hold again.

my3cents

6600 wrote: »

Would something like forefront not be better? Kill the weeds and leave the grass instead of bare ground for the JK to take hold again.

Thats a point thats being made more and more but having been in conflict with this weed for nearly 40 years killing it by whatever means is the main point. A bit of grass that is killed off is very temporary when you look at the larger picture.

Personally I'd be happy to use forefront at this time of year to reduce the amount of growth the JK produces but I'd still hit it with a glyphosate based product in the autumn.

I spray this stuff off for free on neighbors land and the local beach so for me price is a consideration and €50 a year on Roundup Biactive is about as much as I'm prepared to donate to it.

Redsoxfan

Would this stuff be the job for knotweed in a small garden?

https://www.horkans.ie/p/weedfree-360-weed-killer/112000019

Or what else is suitable for non-professional use?

Bass Reeves

Redsoxfan wrote: »

Would this stuff be the job for knotweed in a small garden?

https://www.horkans.ie/p/weedfree-360-weed-killer/112000019

Or what else is suitable for non-professional use?

Ya it gysophate under a generic name

Same product here but cheaper

https://www.google.com/search?q=Weedfree+360+Weed+Killer&client=ms-android-oppo-rev1&sourceid=chrome-mobile&ie=UTF-8

99nsr125

Redsoxfan wrote: »

Would this stuff be the job for knotweed in a small garden?

https://www.horkans.ie/p/weedfree-360-weed-killer/112000019

Or what else is suitable for non-professional use?

It's roundup in a different box

So yes

TomOnBoard

The most important things are

1. Don't cut anything from the standing plants

2. Spray end of August or early September (when you have a predictable dry period ahead) so that the weedkiller is brought down into the roots.

Plan to spray again next May and once more in late August.

K3v

Garlon Ultra is the best herbicide by far to treat JK.

The active ingredients Aminopyralid and Triclopyr are the most effective treatment. Its able to penetrate the waxy leaf of the plant.

Bass Reeves

If leaves are waxy add an activator this soften's the wax and cause the weed killer to stick better.

Markcheese

On a small scale , a little bit of washing up liquid helps a lot , both to get through the waxy coating ,and to get the herbicide to stick ....

Hard Knocks

Bass Reeves wrote: »

If leaves are waxy add an activator this soften's the wax and cause the weed killer to stick better.

Do you spray the entire plant or just the trunk close to the base?

Bass Reeves

Hard Knocks wrote: »

Do you spray the entire plant or just the trunk close to the base?

I say the whole plan never had the problem. I presume it the same as any other plant spray it all

GreeBo

I believe you are better off injecting the stems when dealing with knotweed. Either way a couple of years of vigilance are required to kill it off.
Don't cut anything until you are 100% sure it's dead.

K3v

GreeBo wrote: »

I believe you are better off injecting the stems when dealing with knotweed. Either way a couple of years of vigilance are required to kill it off.
Don't cut anything until you are 100% sure it's dead.

That is mainly the case when using Glyphosate. You can just spray Garlon Ultra on the foliage & it will kill plant & roots.

Redsoxfan

K3v wrote: »

That is mainly the case when using Glyphosate. You can just spray Garlon Ultra on the foliage & it will kill plant & roots.

Is Garlon Ultra available to anyone?

K3v

Redsoxfan wrote: »

Is Garlon Ultra available to anyone?

No it is not. Its for professional use only. You must hold a Hand Held Pesticide or a Boom Sprayer Pesticide cert. Otherwise if you are employing a contractor, you must provide your contractors certification at the point of sale.

Redsoxfan

OK, if I have this bloody thing at all, it's a very small amount. I'd rather try and deal with it myself than paying someone at this stage.

This seems like it might be worth a try

http://topline.ie/garden-outdoors/lawn-garden/plant-lawn-care/lawn-feed-weed-killer/round-up/tree-stump-killer-250ml

Bass Reeves

Redsoxfan wrote: »

OK, if I have this bloody thing at all, it's a very small amount. I'd rather try and deal with it myself than paying someone at this stage.

This seems like it might be worth a try

http://topline.ie/garden-outdoors/lawn-garden/plant-lawn-care/lawn-feed-weed-killer/round-up/tree-stump-killer-250ml

If you have got it early I say spray with roundup and respray next year and keep at it until you wipe it out. Just make sure not to cut or dig any of it.