Japanese knotweed

[judethegreat]

I have years experience of his plant and like all scare stories some people have become very rich on it. I've been at conferences with 'specialists' and they are the ones arriving in the Porsche and Bentleys! I know one company buying a factory that had three small areas along the back wall. The specialist quoted £12,000 for 'specialist' treatment and insurance. Local licensed landscaper I used charged £1,000 in year one for four visits to spray and £200 for each subsequent visit. It was gone after three years.

The plant was imported by Victorian botanists for collections for Kew gardens etc. Ironically it was found to be very good at binding soil and was planted on railway embankments. Now it is out of control in many areas.

It grows using a network of rhizomes, like ginger and turmeric roots, which grow underground and the plant then grows shoots which look like bamboo around this time of year. The flowers in September aren't for reproduction. The plant then dies back over winter, the rhizomes grow over winter and it spreads over the years.

A plant which is left untouched can remain small for many years, go and hack it and the rhizomes will spread further. Getting animals to eat it is a bad move, the rhizome fragments will be spread with their waste and one small piece will be a plant inside a year.

Thanks, good post. And good point about the waste, if all fragments are not fully digested...

 

[AndrewE]

Thank you InOban - Agree inject it - stems are hollow.
New method should be the answer - no poisonous chemicals!

I got rid of it in my garden - and the neighbour's that it was spreading from.
You can use glyphosate etc., but they are best with adjuvents (something like PVA glue) which stick the herbicide to the foliage and gives it longer to be absorbed, or instead inject it into the hollow stems as said above, but it is still glyphosate (and probably a pain to do!)

My system was to cut it off a bit above ground, then put ammonium sulphamate powder into the hollow cut stem. The explanation was that ammonium sulphamate is sulphate of ammonia (fertiliser) "made crooked" so the plant takes it right down into the roots and then gets killed by it. I bought it under the name of "Amcide." Not cheap though. Of course, it's no longer available as a herbicide as no-one will fund the testing required, but if you buy it as a compost accelerator it is still available!

This worked in one year, except that a few spindly bits came up the next. Cutting them off and putting it on the wet surface again seemed to complete the job. I suspect this method wouldn't work on a wider scale though, as the manpower costs would be too high for it to be viable.
A

 

[randyrippley]

I found it easy to clear my garden.
I doubledug it down to around 3 feet, removing and burning all roots.
Over the next three years any new shoots were hoed off. It died.
But if you simply hoe and burn on a monthly basis, after three or four years it will die

PS - what do you think you're eating when you have chinese bamboo shoots............???

 

[Pinus contorta]

Good point about the pigs or goats spreading the rhizome. I think I watched a lecture about the Japanese eating Bracken rhizome once. Didn't appeal. Nor does eating bamboo.

 

[Romsey]

I have also seen what is certainly Japanese knotweed at several locations in the north, as well as the equally concerning giant hogweed.

How well did that work? Would it even come close to killing the plants?

Would it not be better to incinerate that 200m³ of hazardous waste, rather than allow it to continue to grow in landfill?

It's treated like other hazardous waste which isn't incinerated, buried deep in clay lined pits which are finally capped with semi permeable membranes (terram is one) and some metres of clay and inert waste like rubble.

 

[507020]

It's treated like other hazardous waste which isn't incinerated, buried deep in clay lined pits which are finally capped with semi permeable membranes (terram is one) and some metres of clay and inert waste like rubble.

Does that process kill what is left of the plants? What would be the consequences of incineration?

 

[Mcr Warrior]

Does that process kill what is left of the plants?

Burying deep should, hopefully, stop it from growing again.

What would be the consequences of incineration?

You'll get rid of it. The stuff has a high water content though and needs to be dry, and so the problem is two-fold, risk of spreading whilst being stored and dried ahead of incineration, and incomplete incineration resulting in not everything being burnt and so being spread when subsequently disposed of.

 

[al78]

Does that process kill what is left of the plants? What would be the consequences of incineration?

Yes if buried deep enough. Plants require sunlight for the energy to grow, and if the knotweed is buried deep enough, the energy required for it to reach the surface to harness sunlight is greater than the available energy stored in its rhizomes and it will die. Excluding light (with ground cover) is done to control other invasive perennial weeds like couch grass and bindweed. With any weeds that spread prolifically and are hard to eradicate, incineration of the rhizomes is the optimal way of being sure they will never grow back.

 

[a_c_skinner]

Apologies if this has been mentioned but two legal points. Firstly it is illegal to allow it to spread to neighbouring property, it is one of many plants specified in the Wildlife and Countryside Act. Secondly a civil case, Williams v Network Rail Ltd, established that property owners are liable for the damage and loss of value their knotweed might cause to neighbours.

 

[randyrippley]

Good point about the pigs or goats spreading the rhizome. I think I watched a lecture about the Japanese eating Bracken rhizome once. Didn't appeal. Nor does eating bamboo.

Eating bracken was years ago shown to be a cause of bladder cancer in the Japanese population

And so-called "bamboo shoots" are usually one of the Asian knotweeds

 

[Grumpy Git]

And so-called "bamboo shoots" are usually one of the Asian knotweeds

Japan is in Asia.

 

[randyrippley]

Japan is in Asia.

yes but "Japanese" knotweed isn't the only one. And is as much Korean/Chinese as Japanese
There are a host of related species and hybrids, some difficult to tell apart