The war on Japanese knotweed | Hacker News Reader

The war on Japanese knotweed

theguardian.com

85 pointsrapnie37 comments

Knotweed in denmark says hello :-). I've been semi-daily (summer months) cleaning a 2×12 m patch of knotweed for 4 years now, on a house we bought. Currently I have it covered with dark fabric, which I regularly remove to pull up the shoots, then cover again. They should make an aliens movie about that plant.

How is it going? As I understand it, the plant grows roots several meters deep, survives being covered up potentially for decades and can regrow from tiny fragments of root left in the soil. Yes, I have some I’d like to get rid of, too.

Honest question, where does it get the energy and mass? Surely without solar energy, any root system will eventually die. Hell most of the plants that I try to grow suffer that fate despite plentiful sunlight.

The root systems can stretch literally miles.

The roots go 2 meters deep, and can spread horizontally several meters.

Have you tried glyphosate?

I cut the new chutes after about a week of growth and place two drops of glysophate on the stem. Each year I see less and less of them.

I'm not a fan of herbicides in general, but I have to admit that direct application of glyphosate in this manner is extraordinarily effective and, if done correctly, poses almost no risk to other nearby plants.

The amount of effort, I think it would be worth excavating it totally or paying someone to excavate it.

Can you heat treat to kill the knotweed? Like injecting steam into the ground?

Inspired by a demo reel of a ground cooking weed remover, I've experimented with using the tea kettle to kill stuff in my drive way. Works pretty good. A few square inches at a time. I poke a few holes and pour in boiling water.

The industrial size tool covers the ground with a foam, to create a thermal blanket. And then it cooks the ground. It looks like those street pothole fixing tractors, but using steam, instead of flames to remelt the asphalt. (The foam is like a thick bubble bath and will rinse away.)

Just curious. I recently became a "forrest steward" volunteer, and knotweed was specifically called out in training. Do not touch! Immediately escalate!

Ignorant, naive me thought blackberry and ivy were the final bosses.

Here's the plant's CABI Compendium entry: https://www.cabidigitallibrary.org/doi/10.1079/cabicompendiu...

Reading it is quite chilling. Getting rid of the plant is extremely difficult, requiring displacing several meters depth worth of soil, or using extremely toxic chemicals.

There have been some pilot trials approved in Europe (Netherlands, UK) using biological control with psyllids imported from Japan in the recent years. We'll see how that goes.

This struggle reminds me of my personal battle with morning glories, nadinas, and bermuda grass, and a neighborhood effort to remove several ailanthus from along a local creekbed. Rhisomatic weeds are just a style of plant that we've never developed a good strategy for, outside continuous poisoning with something like glyphosate.

If you do ever see an ailanthus seedling, dig it out if you can. They're terrible and I've even seen them crowding out young redwoods here in northern CA. https://extension.psu.edu/tree-of-heaven

I think in college I rented a house where ailanthus was growing up through the lawn. Every year we pulled starts out and the foul odor in that description makes me think that was it.

I'd like to add horsetail to that list.

https://www.cabidigitallibrary.org/doi/10.1079/cabicompendiu...

Dig out every single sapling too. I despise those trees so much here, they take over every thing and smell awful. Their root system when they're larger is expansive, I had to use a backhoe to dig out enough of the root system to get it to stop spreading and now it's a non-stop battle digging out the saplings. Previous owners loved the look, or it showed up by accident, but a 30' tall tree of heaven is no joke to exterminate.

"Once hailed as a ‘handsome’ import, this most rampant of plants has come to be seen as a sinister, ruinous enemy"

Those importers should have taken the name "knotweed" into account.

Maybe they heard "not weed".

We have this lovely new plant, Strangleweed Landchoker

Perhaps the Japanese name is more appealing.

"In Japanese, the name is itadori (虎杖, イタドリ). The kanji expression is from the Chinese meaning 'tiger stick'. One interpretation of the Japanese name is that it comes from 'remove pain' (alluding to its painkilling use), though there are other etymological explanations offered." (https://en.wikipedia.org/wiki/Reynoutria_japonica)

'Dog Strangling Vine' is a nasty invasive in north america.

https://www.invadingspecies.com/invaders/plants/dog-strangli...

I’m sorry Frye, but astronomers renamed Uranus in 2620 to end that stupid joke once and for all.

What’s it called now?

Urectum.

Netherlands here, I have a patch in my garden that I weed continuously from april to september. We eat the shoots. In Japan Thei call it "sansai" and they are quite good. It tastes like artichoke.

"sansai" or 山菜 just means mountain vegetables. It is just a catchall term for any edible plant found in the wilderness.

Thanks for sharing the specific meaning. Anyhow, it is quite tasty! ;)

You know how there are those plans to gene-hack mosquitos into sterility? Could we make an “herbicide” that’s actually a bacterium carrying a knotwood-specific CRISPR program, to do something drastic and awful to crucial portions of its DNA — and then just spray it on one part of an infestation, and wait for it to spread across the whole soil-connected colony?

That’s generally been my thought on how to deal with invasive plants (and probably insects). We’d need to assuage public concerns first in order for the strategy to be accepted, however. But ultimately I think there is huge potential for such highly targeted control, and I look forward to its use in North America for eliminating invasives.

Why do many resveratrol supplements contain Japanese knotweed? Which part of the plant secretes that?

The highest concentration is in the root.

Am I missing something? We have knotweed, we just tear it out and that's it.

Yeah not sure, growing up we had a swampy area of our property covered in it, was really fun to run through as little kids and cut them down with stick swords. Our parents finally realised they needed to sell the property and eliminated them all over two years, not sure what the big issue is.

The title is misleading, almost thinking that Japan is waging war again

I don't think it is that difficult or expensive to control knotweed using modern methods, at least on a small scale. I started investigating this in order to control a persistent patch of knotweed at my parents' home, but unfortunately, the patch was cut down before I could implement what I think is the most safe and sustainable method, at least for isolated patches: stem-injection or hack-and-squirt with the herbicide imazapyr.

Imazapyr is slower-acting but more effective than other herbicides. As you can see in this study, which compared several herbicides applied with spraying, the imazapyr formulation performed worse than all others for up to 58 days, but after 333 days, the knotweed was 95% gone, better than any others, even the formulation that mixed imazapyr with glyphosate.

Evaluation of Imazapyr, Glyphosate, and Triclopyr for Japanese Knotweed Control https://weedscience.ca.uky.edu/files/japaneseknotweed2005.pd...

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Here’s another study - 96% of imazapyr-treated trees were in the highest defoliation class vs. 62% for glyphosate:

Efficacy of ‘hack and squirt’ application of imazapyr, triclopyr, and glyphosate to control the invasive tree species Chinese tallowtree | US Forest Service Research and Development

https://www.fs.usda.gov/research/treesearch/35461

"These results indicate that imazapyr can be used to eradicate Chinese tallowtree by ‘hack and squirt’ injection without short-term (12 months) damage to dominant live oak trees."

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Controlling Knotweed in the Pacific Northwest (this mentions stem injection using glyphosate)

https://www.invasive.org/gist/moredocs/polspp01.pdf

"Although time-consuming, not only does this approach essentially eliminate drift, but Clark County (WA) Weed Management reports obtaining 100% control in one treatment by injecting 5 ml of 100% Aquamaster or Round Up Pro into each stem of a given clump. More than 20 patches were so treated"

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Here they also use glyphosate: https://web.archive.org/web/20030404152410/http://www.co.cla...

"If 38 of 50 canes are injected, expect the twelve that were NOT injected to survive and reproduce. EACH CANE HAS ITS OWN SEPARATE RHIZOME SYSTEM. Even though the injection process is initially time consuming, it is more cost-effective than several trips to the same site for foliar applications made over years with minimum results."

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None of these studies mention the specific technique of using stem injection with imazapyr, which I think is likely to be the most effective method. Although I haven't yet tried imazapyr on knotweed myself, I used an extremely minimal amount to kill several different species of obnoxious shrubs.

I used it to kill:

- Japanese barberry

- Sumac

- Elm saplings

- Fox grape

All these had been growing from the base of the external walls of my parents' house and had been uncontrolled for decades despite (probably-not-frequent-enough) cutting.

The amount I used was maybe a fluid oz. in total for all of these, and that was probably overkill. I just cut a flap into the bark in such a way as to maximally expose the cambium, then applied a few drops and tied the flap closed with some string. I did this to some sumac suckers right in the middle of a bunch of my mother’s day lilies and my stepfather’s blueberries and they weren’t affected at all.

In the case of the sumac and others, it took a couple weeks before the plant was visibly wilting, but after a while, even untreated suckers several yards away died. The fox grape didn’t show signs of wilting at first, but was dead by the following spring (I treated in early July, which is actually less than optimal. Late summer is recommended because of the predominant direction of sap flow at that time - from the leaves to the roots)

I have a meat syringe which I plan to use to inject knotweed when the opportunity arises.

This title is ridiculous

Eh, it's pretty normal, see also War on Drugs, War on Terror, War on Poverty, War on Want etc.

The whole article is tongue in cheek.

A few dashes of hyperbole improves the flavour and helps with the digestion – particularly for longer texts.

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