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Killing Japanese knotweed

When it comes to killing Japanese knotweed, treatment and eradication can be a tough task – but it is possible with commitment.

Herbicide spraying is a popular treatment for eradicating Japanese knotweed. However, it’s important to know that herbicide will kill most of the plant, but it doesn’t get rid of the plant’s rhizomes in the ground. This means that future re-growth is technically possible if not managed.

Repetitive, yearly applications of herbicide can prevent the spread and growth of Japanese knotweed, but if you want the knotweed’s rhizomes (roots) completely removed from the soil – excavation is required. This is the way to ensure complete Japanese knotweed removal.

Herbicides that Kill Japanese Knotweed

Does Roundup kill Japanese knotweed?

Roundup, Gallup, Landmaster, Pondmaster, Ranger, Rodeo, and Touchdown are all herbicides recommended to kill Japanese Knotweed. They are all glyphosate-based herbicides and will kill the troublesome weed.

The best time to spray the leaves of Japanese Knotweed with herbicide is late summer or early autumn. This is the period in which the plant is flowering and so the foliage conducts more nutrients to the rhizome to build food reserves.

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About glyphosate-based herbicides

Glyphosate-based herbicides will kill Japanese knotweed, but be careful, since these are non-selective herbicides, they, will kill whatever plants they come into contact with, whether that’s Japanese knotweed or your prize geraniums. For this reason, many gardeners don’t like using herbicides, but in the case of Japanese knotweed, it is one of the few really efficacious solutions.

Glyphosate is a translocated herbicide as opposed to a contact herbicide. While contact herbicides may appear to be effective against Japanese knotweed, they are in fact only killing its leaves and shoots. This is why it is best to use a glyphosate. As a translocated herbicide, glyphosate is taken down into the plant’s roots where it destroys the species.

How long do glyphosate herbicides take to work?

Glyphosate-based weed killers available from garden centres will all have a harmful effect on Japanese knotweed. This is normally a slow process requiring at least three to four growing seasons to be effective, and fully eradicate the Japanese knotweed. Professional Japanese knotweed removal companies have access to more powerful herbicides which can reduce the removal process by half.

Are there any other chemicals that kill Japanese knotweed?

Japanese knotweed is also susceptible to other chemicals like triclopyr and picloram. However, glyphosate is often the preferred choice for domestic use due to its suitability for use near water.

A word of warning with herbicides

While herbicides are an effective means of eradicating Japanese knotweed, their use should be limited to areas destined to become lawns or flower beds, do not use herbicides on areas that will one day become your vegetable garden.

Stop trying to eradicate Japanese Knotweed yourself!

Did you know knotweed can regrow with only a thumbnail's worth (around 0.2g) of its root system left in the soil?
We can help provide a solution that lasts.
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Stop trying to kill Japanese knotweed yourself!

Did you know knotweed can regrow with only a thumbnail’s worth (around 0.2g) of its root system left in the soil?
We can help provide a solution that lasts.

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Common Japanese Knotweed Killing Misconceptions

Can you kill Japanese knotweed with bleach?

No, you cannot kill Japanese knotweed with bleach. All it will do is cause more damage to your garden and the environment surrounding its application. We would not recommend wasting your time using this household product to try and treat your knotweed problem, even if it has some effect on its growth – it will not be sufficient in any way.

Can you kill Japanese knotweed with vinegar?

No, there is no hard evidence that vinegar is successful at eradicating Japanese knotweed, and like bleach, we would not recommend wasting your time using this condiment on your knotweed problem.

Can you cut back Japanese knotweed?

Despite websites like Wikihow claiming that Japanese knotweed will not regrow from cut canes, cutting back knotweed alone will not do anything and will not kill it. It will grow back – take it from the experts.

Other Viable Options for Killing Japanese Knotweed

Burning Japanese knotweed

Once Japanese knotweed has been removed it can be burned on your own land, but you will first need to let it dry out thoroughly. However, even after burning Japanese knotweed, the rhizomes may still be active and are capable of growing a full plant when they next come into contact with soil and water. For this reason, even after burning, you will need to contact a professional Japanese knotweed eradication company.

Stem injections

In more environmentally-sensitive areas (when you do not wish to damage neighbouring plants), there is also the option for herbicide stem injections instead of herbicide spraying. This treatment method is often chosen on residential projects due to the precise nature of the application.


There are also cases where a more immediate removal strategy is required. In these instances, the best option is a Japanese knotweed excavation. By digging up the infected area, it’s ensured that any trace of Japanese knotweed is removed. This is essential since even the tiniest fragment of rhizome left in the soil can regrow. Excavation is the only available removal technique if the land in question is to be used for future development purposes.

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Risks of Failing to Eradicate Japanese Knotweed  

From costly fines to damaging pipework, failing to kill Japanese knotweed fully can lead to multiple problems when not managed:

  • Costly fines – if you allow Japanese knotweed to spread to neighbouring land, you could land yourself a £5,000 fine.
  • Difficulty getting a mortgage – additional steps may be needed when buying or selling with Japanese knotweed present, and may even be refused dependent upon the lender.
  • Risk of subsidence – if your property has weak spots, you may be at risk of subsidence where Japanese knotweed roots create ground movement.
  • Damage pipework and buildings – Japanese knotweed’s deep roots take hold underground, and can even penetrate through foundations and pipework.

Important Information Regarding Knotweed Disposal

When it comes to the excavation and disposal of Japanese knotweed, a licenced waste carrier, such as Japanese Knotweed Specialists, must be used as knotweed is a controlled substance.

Alternatives to Removing Japanese Knotweed

Root barriers to prevent spreading

Used purely as a means of halting the spread of Japanese knotweed, the installation of a root barrier is an option. This impenetrable barrier goes down three metres (Japanese knotweed roots go down just over two) and therefore stops the plant spreading into any neighbouring lands. The Japanese knotweed root system (rhizome) cannot grow through the root barrier and thus the infestation is completely contained.

Japanese Knotweed and The Law

From the Anti-social behaviour, Crime and Policing Act 2014 to Hazardous Waste Regulations 2005, there are multiple acts here in the UK that mandate the treatment of Japanese knotweed.

While it is not illegal to have Japanese knotweed present on your land, it is an offence to let it grow knowingly to neighbouring lands according to the Wildlife and Countryside Act 1981. Failing to eradicate Japanese knotweed and letting it spread from your land may land you a fine of £5,000 or even a prison sentence.

Don’t get caught out. Ensure you fully eradicate Japanese knotweed to avoid costly fines or worse.

Contact a professional Japanese Knotweed Removal Specialist

Eradicating Japanese knotweed is a difficult process and can take a long time to complete. We normally suggest about two years – four whole growing seasons to be sure. Some people take it on themselves to remove this troublesome plant, but the problem is that even a 0.2g fragment of Japanese knotweed rhizome can regrow – leaving you back where you were at the start.

The best way to ensure a complete, thorough and lasting eradication is to contact a professional Japanese knotweed removal company like Japanese Knotweed Specialists.

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Speak to one of our Japanese knotweed removal specialists now on 0800 122 3326 or fill in our contact form by following the link below.

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