Japanese Knotweed - Renouée du Japon


We have in our small hamlet the beginnings of the dreaded Japanese Knotweed. I notified as a first port of call, the communes Mairie but never received acknowledgement. This year, the unwelcome, rampant and invasive visitor is gaining more ground and several locals are showing more concern now as to what can be done to eradicate it.

My question to the forum, is does anyone know of a government department which we could notify of this situation?



Where we live, in the 'Parc Régional de la Haute Vallée de Chevreuse', we have been asked by the parc authorities to notify them when we see it in our communes. They want to map out several invasive species, so they can be managed. However, I don't believe they are actively trying to eliminate the stuff. Every year the knotweed creeps a bit closer to us... Not many people in France understand the menace, as far as I can make out. But I can't say that my contacts are a scientific sample! I do not know of a national body responsible for 'notifiable' weeds. Sorry. There may be something like our 'parc' near you.

Knotweed has the reputation for being impossible to eradicate but it isn't true. Cut it down to just below the first joint and burn the cuttings. Fill the hollow stem with Roundup. Top up as the Roundup level drops. It isn't immortal.

The problem is when it gets out of hand. I have destroyed a small patch of knotweed near my house, using Jon's method. It is very effective, and easy on smaller patches. It's harder when the patch is bigger, such as along the railway lines into Paris.

We are not allowed to have bonfires here (The Essonne). Everyone should check the rules on that. Here, it is to reduce air pollution. I put invasive weeds into the non-recycled rubbish, as it is burnt for 'chauffage urbain'. Not a good option if your rubbish goes to landfill.

When I was early retired and needed extra money, when my paintings were not selling, I created a new vegetable garden for the owner of a Regency mansion. Right there was a rampant knotweed. I surgically removed the b*stard, right through its root system. The roots are red, so easy to follow. The boss had plenty of dosh, and let me get on with it. It took me a number of days: I wish I knew, over 20yrs ago, the Roundup method. I had a mountain of horse manure to dig in. No Rotavator, but good old spade work! They were pleased with my efforts, and I sorted out their flooding problem with their new pond on the front lawns, installed by the landscapers there at the time. One needs an overflow system: duh!

One of my paintings. "Flock Coming Home" Scotney Castle Estate, where Maggie Thatcher had a weekend retreat.

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I used the same method as Jon and it worked well, though it took three years to get rid of the invasion altogether.

Years ago I helped run a nature reserve in the UK, and we were assured that cut knotweed MUST be well dried before burning or it can just spread where any life fragments fall. Round up will work - anything with glyphosate should work - but do it now, drench the leaves and repeat as new growth pushes up. Cut and dry dead stems, then burn. At least 3 applications by September and buy in stocks for next spring, probably the one after as well. It must not be composted or put with green waste, and if you dig up any roots, their fragments can sprout.

It is a problem in our area, and the authorities don't check it often enough, cutting it down every summer isn't enough. It has spread down the length of some rivers, nd was left far too long before treating.

JKW is covered by strict laws in the UK, as per usual, France is 20 years behind the times. There is no legislation regarding treatment/eradication and it is has only recently been considered a problem but not serious enough for a national strategy campaign.

The problem is that if you leave just 1cm of root in the ground, it will grow back. Round-up will shortly be on the banned product list by the way, but injecting each stem with the afore-mentioned (or diesel - very illegal but also very effective) will reduce the activity but you will need to repeat the procedure regularly for the next 5 years. Any foiliage and roots will need to be incinirated, not just dumped over your neighbours wall.

Alas there are no training courses available in France regarding JKW treatment, otherwise I would have done it and made my fortune. There are training programmes available in the UK but guess what, they're not valid in France!

I will contact CEPA (Confederation European Pest Management Associations). I'm not a member, it's too expensive for a "boys club" that need dentures, but there's no harm in asking them the question.

I will keep you informed, but don't expect a rapid response. I will meet with their directors in Paris in November regardless.

In the meantime, as the treatment of JKW comes from local budgets, nobody will touch it. So at the moment, it's all for one and one for all.


I'm not sure of the legalities re the use of weed killers in France but we live on a farm in Wales and have totally iradicated our JKW with glysophate liquid spray. My husband did our friends garden in the local village as well as it was invading her neighbours, and so far this year, it hasn't emerged again, unlike the JKW which was burnt by someone down the road and its come back stronger than ever. It needs to be sprayed as soon as it gets a good head above the soil, and if it does come back spray as soon as you see it. Note: glysophate will kill everthing EVERYTHING! with a leaf so be careful if you do spray near to your loved plants.

'Don't put it out with green waste' can't be emphised enough. But people do and hence using compost from the local tip (because there's no attempt to sterilise it) almost guarantees that it will spread.

Glysophate has been banned from our village "services technique", but it isn't banned for personal use, or on local farms here, in the Essonne.

I did hear it was going to be banned in the UK but not sure if that means just for people who don't have a holding number/licence?

I understood there was to be a vote in the EU for either prolonging or banning the use of glysophate. The current licence expires in June, I think.

But you are not allowed to burn it outside either. Garden waste is considered to be part of your 'domestic' rubbish, and is illegal to burn it in France unless there is no garden rubbish collection in your commune:


The fine is €450, but I've never heard of it being enforced.

And burning the stuff is illegal in open bonfires in any case! (Unless you are a garden professional) I'll be interested to hear what CEPA says.

Just an update regarding CEPA as requested.

CEPA deal with pests with a hearbeat therefore JKW is not a recognised pest with them.

I guess it's back to square 1 and maybe contact needs to be made with the Environment Agency, whoever they may be.

Aploogies for the lack of news but I'll enquire at the European Pest Control Exhibition in Paris in November...hopefully more news then and we can come up with a solution (start) next year,

The JKW are coming into flower at the moment, so [responsibly] cut and burn as much and as soon as possible is my personal opinion.


Came across this: http://www.juvisy.fr/wp-content/uploads/2012/04/renouee.pdf which suggests cutting it down, bagging every scrap, and incinerating it. This doesn't match what we were advised to do in the nature reserve 30 years ago. Industrial incineration, maybe, but not a bonfire as bits can fly off and grow elsewhere. Also, any bits which don't get bagged can restart growth. It doesn't just spread through the roots. In the UK, it is now an offence to ignore JKW or let it spread (neighbouring properties can be impossible to sell), but the French just wait and see.

Which contradicts the national ban on burning garden rubbish in France, which is enforced to a greater or lesser degree depending where you live.

We have a patch about 1 metre square growing in a field next to ours. I would say it is about 100 metres away from our boundary. Should we notify the mayor? The field gets cut for hay.

When we came to France in 2005, there was a Garden Centre not to far from us that was actually selling JKW in smallish pots for 2.50 Euros per pot…Sue went and spoke with the Boss but just got a shrug…

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