How to kill Japanese Knotweed

Herbicides, chemicals and excavation methods

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.

Does glyphosate kill knotweed?

Yes, glyphosate-based herbicides will kill Japanese Knotweed. But be careful, since these are non-selective herbicides and as such, 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 rhizomes, preventing regrowth.

What herbicide kills Japanese knotweed?

Japanese knotweed is susceptible to a range of herbicides including glyphosates, such as ‘Roundup biactive’ and ‘Glyphos biactive’. It 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.

While herbicides are an effective means of killing Japanese Knotweed, they 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.

What chemical will kill Japanese knotweed?

Glyphosate-based weed killers available from garden centres will all have a harmful effect on Japanese Knotweed. Glyphosate is often applied to the leaves, which the plant then takes down to the rhizomes. 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.


Will diesel kill Japanese knotweed?

The short answer is no. This old trick is not an effective way of killing your Japanese Knotweed. In order for a herbicide to be effective, the plant in question needs to take the poison down to its roots and basically, the plant won’t do this with diesel. All you will end up doing with diesel is ruining your soil and making it unusable in the future. And at the end of the day, you will still have a Japanese Knotweed infestation to deal with.

How do you get rid of knotweed?

The most common and economically effective means of removing Japanese Knotweed is herbicides. These may be applied to the leaves, which the plant then takes down into its roots, or in more environmentally-sensitive areas (when you do not wish to damage neighbouring plants), there is also the option for herbicide stem injections.

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, we ensure 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.

Can you burn 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 removal company.

Alternatives to removing Japanese Knotweed

Used purely as a means of halting the spread of Japanese Knotweed, we can also install a root barrier. 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.

Contact a professional Japanese Knotweed removal specialist

Removing 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 trouble plant but the problem is that even a 0.2 g 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.


Our house purchase was held up when we were refused a mortgage at the valuation stage, when a survey commissioned by the bank showed that Japanese Knotweed could be present on the property. This really slowed down the process. It feels like an unreasonable extra expense and an unnecessary cost. Thankfully, Japanese Knotweed Specialists charged a very reasonable fee to carry out a Japanese Knotweed survey to find there was in fact no trace of the weed on the property, so the sale could go ahead. Thank you Japanese Knotweed Specialists. Property developer Peri, London
We recently purchased a property in the Bromley area. The initial mortgage valuation survey reported the presence of Japanese Knotweed growing on the railway embankment at the end of the garden. The mortgage lender advised that before they would consider approving our mortgage application, we would need to hire a JK specialist to inspect the growth and provide a detailed report on the findings. We duly approached Japanese Knotweed Specialists and Adam came round to carry out a survey. Thanks to his full and detailed report on the Knotweed, our lender was satisfied and (subject to a treatment programme being implemented) approved our application and we were able to proceed with the purchase. Japanese Knotweed Specialists have now commenced their 1st treatment to eradicate the JK and their service is always friendly and helpful. Mr Winsor, Bromley
Many thanks for such a speedy turnaround of this report. As I said yesterday, this has been an extremely worrying time for us, but the efficiency, professionalism and helpfulness shown by you and Tanya has been second to none, and has made a difficult situation that bit easier to handle. Arleen, Derby

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