Japanese Knotweed, anyone?

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Japanese Knotweed, anyone?

Post by vizzle »

Hello there, people of Sydenham

I just moved into the area a month ago and I'm loving it.

What I'm not loving is reports from neighbours of Japanese Knotweed in our gardens. Has anyone had experience of it? I've done some light Googling and discovered May is the time when it grows like, er, Japanese Knotweed. Just wondered if it was a common thing round these parts.

Tim Lund
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Re: Japanese Knotweed, anyone?

Post by Tim Lund »

It's common in many parts, including here. There are fine growths of it to be seen behind Platform 1 of Sydenham Station. Control is notoriously difficult, but the standard way is to use a systemic weedkiller such as glyphosate, marketed as RoundUp by Monsanto, but now out of patent protection, so available from other manufacturers.

Systemic weedkillers work by being taken down from the leaves on which they are sprayed into the roots, so killing the whole plant. The only alternatives for plants with underground stems, such as JKW, are (1) to dig them up, taking care to get every last bit of them, and for the sake of others, burn them or destroy it chemically in some other way, or (2) to cover them with some impermeable barrier for enough years for the nutrients stored in the underground stems to give out - which is a long time.

Systemic weedkillers work best when plants are focusing on taking nutrients down from the leaves to the underground stems, in other words in the autumn, when preparing for winter, but that doesn't mean it's not worth applying them now - just it will take more applications.

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Re: Japanese Knotweed, anyone?

Post by stuart »

Tim Lund wrote:There are fine growths of it to be seen behind Platform 1 of Sydenham Station. Control is notoriously difficult, but the standard way is to use a systemic weedkiller such as glyphosate
Is this on National Rail/TfL land and is someone doing something about it?


Tim Lund
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Re: Japanese Knotweed, anyone?

Post by Tim Lund »

Here's the RHS on the matter

Scotts Roundup Tree Stump & Rootkiller has label recommendation for controlling Japanese knotweed, instructing it to be applied to the cut canes

Alternatively, try other tough formulations of glyphosate (e.g. Scotts Roundup Ultra 3000, Scotts Tumbleweed, Bayer Tough Rootkill, Bayer Super Strength Glyphosate or Doff Knockdown Maxi Strength Weedkiller)

Glyphosate is usually applied to the foliage and is passed within the plant to the underground parts

It is useful to cut away old stems during the previous winter to allow good access. The best time for spraying with glyphosate is at the flowering stage in late summer. However, it is difficult to spray at this stage, when the weed is 2.1m (7ft) or more high

A more practical approach is to allow Japanese knotweed to grow to about 90cm (3ft), which will usually be reached in May, and spray then. There will be regrowth and consequently a second application in mid-summer is useful. Check during September and if it has grown once more, spray again before growth begins to die down in the autumn. Check again the following spring

Avoid spray coming into contact with garden plants. Glyphosate-treated knotweed will often produce small-leaved, bushy regrowth 50-90cm (20in-3ft) in height the following spring. This is very different in appearance to the normal plant and it is essential that this regrowth is treated

It usually takes at least three to four seasons to eradicate Japanese knotweed using glyphosate. Professional contractors, however, will have access to more powerful weedkillers that may reduce this period by half

Roger Mellie
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Re: Japanese Knotweed, anyone?

Post by Roger Mellie »

I learned a lot about this recently as we were looking at buying a property where it was found in the garden.

It is treatable, and there are professional firms that do this - just cutting it down yourself is a big no-no and will exacerbate the problem (and is illegal)

There are plenty of scare stories around if you do your googling - however do be aware that mortgage lenders treat it as very high risk, and some will just not lend if it is found within 7 metres of your house - this includes on a neighbouring property.

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Re: Japanese Knotweed, anyone?

Post by marymck »

You can get something to inject into the stems. This is very effective. I knew someone whose garden was taken over by the stuff and she injected the stems regularly and every single bit eventually died and ten years later it has not returned.

I believe we're very lucky in this country in that our winters are too warm and wet to allow for spread by seeding. Japanese knotweed in this country only spread by underground runners. That's why it's so important to kill every last bit of an infestation. And why it's illegal to dispose of it in landfill! It's also why it spreads so easily trackside.

The old council depot off Willow Way is plagued with it. The site is about to be cleared and a report has been carried out that you might find informative.

I will try to post a link ...

http://planning.lewisham.gov.uk/online- ... CAPR_73378

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Re: Japanese Knotweed, anyone?

Post by Tadpole »

There's knotweed in the green at Cobbs corner. It's spread to the garden next door to me. I did inform the council who said they were aware of it and monitoring it.

It's not illegal to cut it down, it's illegal to dispose of it using a council dump or dumping it anywhere. It can be burned.
You can get a syringe and fill it with undiluted Glyphosate and inject it into each stem. This is best done July/August. It will reappear the following year but be deformed and smaller. Repeat weed killer in the summer and if you're lucky it will be gone, if not you may need to do it again another year.

Cleared 15' x 20' patch of it years ago from my sons garden doing the above and it's still never come back.

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Re: Japanese Knotweed, anyone?

Post by simono »

Just a quick word to say that any waste from these plants can only be disposed on in controlled sites. A single piece of live material will grow into new plants. Consult the council before dumping any waste at all and you can be prosecuted if you do not

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