Finding the best weed killer to kill Japanese knotweed can be a challenge when you consider how many are on the market and some work better than others.

Japanese knotweed is a nasty invasive plant that causes serious damage to biological diversity, human activities, and the environment in general.

The tenacious root system that can grow 3 metres deep and 7 metres wide in any direction is also bad news as it can lead to the destruction of buildings, roads, fences, pavements etcetera.

As soon as you spot this weed plant growing near your property, you should act fast and figure out the most effective way to eliminate it completely.

The use of weed killers to kill Japanese knotweed is one of the most effective methods to get rid of this invasive weed plant weed.

Notwithstanding the type of weed killer chosen from the many existing varieties, you must ascertain that it is strong enough to get to the rhizome of the weed plant and destroy it completely failed to which the plant will easily regrow.

In this context, we are now going to deliberate on the best weed killer to kill Japanese knotweed as detailed below:

Factors to consider when deciding on the best weed killer for Japanese knotweed:

Application method

The most effective way of applying a weed killer is through direct spray because this will guarantee that the chemical extends to the rhizome of the plant.


A good weed killer should have the active ingredient called glyphosate which should have a concentration of about 41% for good results.


The weed killer must always act fast on the weed plant and show results within a short timestamp.

Assessing the Best Weed Killer for Japanese Knotweed

This section will review and amplify the best weed killer for the eradication of Japanese knotweed among the various varieties that are considered the best when it comes to the removal of this highly invasive weed plant completely.

As we elucidate on some of the best weed killers out there, we will also match their pros and cons to help you understand their efficiency.


This weed killer makes the cut for containing 41% glyphosate and it has been commended for eliminating the Japanese knotweed within 7 days after a single application.

Its pros are that it can get to the roots of any weed and effect destruction; it is rainproof and can act on numerous weed plants.

A single container of this weed killer can be applied to a property covering up to 25,000 square feet. However, if not used within 90 days, its effectiveness is significantly reduced.


This is a no-mix formula that acts fast even on the stronger weeds that seemingly won’t go away.  There is a pump and sprayer attached to it such that you can easily apply them around your gardens or vegetables without any unnecessary spillage.

This weed killer delivers quick results when applied appropriately to Japanese knotweed.

The reason why this weed killer is highly ranked is because of its ability to be absorbed through the leaves of the Japanese knotweed and trickle down to its roots and ensure that there is the destruction of the entire plant. Talk about taking no prisoners!

Additionally, you do not need to constantly go through the trouble of mixing any contents as Roundup is made ready for use. Roundup is easy to use and provides a quick way to get rid of Japanese knotweed. 

All the aforementioned factors considered, Roundup makes the cut as one of the best weed killers to kill Japanese Knotweed.

Roundup weed killer to kill Japanese knotweed
Roundup weed killer to kill Japanese knotweed


This weed killer contains approximately 43% glyphosate making it a strong contender as one of the best outstanding weed killers for Japanese knotweed. Once applied, it swiftly acts on the weed plant and brings to an end any re-growth for at least one year.

Also, it is rainproof (two hours) thus; one can rest assured that it will not be washed off by rainwater in case it decides to pour immediately after applying the weed killer.

The most exquisite thing about this weed killer is that it contains two herbicides and a surfactant to deliver the permanent removal of Japanese knotweed.

The only handicap of this particular weed killer is that it is relatively expensive compared to other weed killers that are used for the same purpose.

RM43 weed killer to kill Japanese knotweed
RM43 weed killer to kill Japanese knotweed

Ortho GroundClear

This weed killer for Japanese knotweed does not contain glyphosate but it stands out based on its ability to kill weeds and prevent any re-growth at least for one year long even through a single application.

The weed killer acts fast and its effects are instantaneous. It is capable of getting to the root of the weed plant and can also resist rain for at least one hour after application. However, it is well and truly able to remove and kill Japanese knotweed within 3 hours of application.

Ortho weed killer to kill Japanese knotweed
Ortho weed killer to kill Japanese knotweed


This is a concentrate that kills weeds. The upshot of this weed killer for Japanese knotweed is that results will be visible just after a time frame of 3 hours after application.

It is also able to resist rainfall that may last as long as 15 minutes or more and most importantly, planting can take place just after one day has elapsed from the time of its application.

The only shortcoming of this weed plant is that being a concentrate, one has to ensure that they have an ideal formula every time one intends to use the weed killer and this can be challenging or tiresome.

Spectracide weed killer to kill Japanese knotweed
Spectracide weed killer to kill Japanese knotweed


Certainly, there is quite a big variety of weed killers for Japanese knotweed out there but the ultimate factors that will help you identify the best from the rest are the ability of the weed killer to act instantaneously, resistant to rainfall, contain glyphosate, and eradicate the weeds within a short period of time.

When choosing a weed killer, you must ensure that it makes the cut to give you effective results because failure to consider the important aforementioned factors may lead to an exercise in futility since the weed killer you chose may not act on the weed plant as desirable as you intended it to be.

Want to know more about the best weed killer to kill Japanese knotweed?

Knotweed Removal aims to provide the most up-to-date information, help and advice for YOU to make informed decisions. If you are unsure or uncertain about how to proceed, please reach out to us and we will gladly come back and advise you as best we can.

Governmental advice can be found here and the UK law covering the removal of Japanese Knotweed as stated under the Wildlife and Countryside Act 1981 can be found here.

The best means to contact us is via our email –

Do not forget we have a library of blogs covering many areas relevant to Japanese Knotweed, our free downloadable How-to Guides and Product Reviews on the latest methods being employed to eradicate or remove Japanese Knotweed.

Knotweed Removal, UK

Bestseller No. 1
Bayer Garden 2 x Path, Patio & Drive Weed Killer & Watering Can Set - 3 x 8g Sachets per pack treats upto 75sqm - Kills Ground Elder, Nettles, Docks, Couch Grass & Japanese Knotweed.
  • This exclusive twin pack and 9L Watering Set is everything you need for clearing weeds from paths, patios and rives including areas of tarmac, concrete and block paving.
  • Kills tough weeds and their roots including: Ground Elder, Nettles, Docks, Couch Grass, Japanese Knotweed, Brambles, Bracken & Ivy.
  • Each box contains 3 x 8g Simple ready measured soluble doses and treats up to 75sqm. Apply at any time when weeds are showing green leaf and are actively growing.
  • Sold with our durable 9L or 2 gallon capacity galvanised steel watering can with removable brass rose. Colour cannot be guaranteed. Watering can will be randomly picked and despatched.
  • Keep children and pets away from treated areas until the spray has dried.
Bestseller No. 2
Roundup Tree Stump Weedkiller, Super Concentrate 250 ml
  • Kills ivy japanese knotweed, saplings, brambles and nettles to the root
  • Kills up to 16 tree stumps
  • Contains a reusable pipette for specialist treatment of japanese knotweed
  • Kills the roots so weeds don't come back
  • Degraded in the soil by micro organisms
SaleBestseller No. 3
Weedol 011005 Pathclear Weedkiller Liquid Concentrate, 6 + 2 Tubes
  • Unique dual action fomulation, kills weeds to the root and prevents new weeds growing for up to 3 months
  • Ideal for paths, drives and patios
  • No measuring or mess - just add water
  • Creates an invisible barrier that prevents new weeds for up to 3 months
  • Children and pets need not be excluded from treated areas (once dry)
Bestseller No. 4
RootBlast - RootBlast 360 Glyphosate Home Garden Weedkiller - 1L Bottle with Integral Measuring Device Pair - Includes Pair Of gloves - 1L Makes Up to 50L
  • WEED KILLER CONCENTRATE: Rootblast's strong weed killer is both super-concentrated and tough on most broad leaf and grass weeds. It's specifically designed to bring you the best results by using systematic herbicide technology. It targets weeds from the inside and kills them at their underlying roots, preventing any future growth
  • GLYPHOSATE WEED KILLER: For optimal weed control, Rootblast have created a concentrate weed killer that contains 360g/l of glyphosate. Glyphosate is a broad-spectrum systemic herbicide and crop desiccant that is used by famers. It kills and destroys the weed without affecting the crop. By using glyphosate, Rootblast's weed killer is stronger and more effective than most other weed killers on the market
  • GLYPHOSATE HERBICIDE: This powerful and effective weed killer is designed to target weeds such as dandelion, grasses, docks, nettles, willowherb, bindweed, woody brambles, tree stumps, ivy and more. After applying Rootblast's heavy duty weed killer, the first signs of weed control are visible when the weed leaves yellow - this can take anywhere from a few days to up to 2-4 weeks. From this 1 litre bottle of glyphosate herbicide concentrate, you can make up 50 litres of product when it's diluted
  • DOCK, GRASS & DANDELION KILLER: Alongside this industrial strength weed killer, you'll receive a pair of protective gloves as well as the integral measuring device attached to the bottle. The gloves provide you with protection to ensure your experience is as easy and safe as possible. The integral measuring device is an inbuilt measuring cup, simply remove cap and carefully squeeze the container until the cup is full
  • TOTAL PROTECT WEED GARDEN SPRAY: This easy to use product is available as a ready to use tough, concentrated weed killer that comes with a integral measuring device attached and protective gloves. Use by professional garden and farmers, this product can tackle your weed problem and kill the weed from the root - the ultimate weed killer!
Bestseller No. 5
Rootblast Glyphosate Weedkiller 4 x 100ml Concentrate with 5L Pump Sprayer
  • For use on unwanted vegetation and areas not intended to bear vegetation
  • Contains 72 g/l glyphosate for effective control of annual and deep-rooted perennial garden weeds, including grasses*, docks, nettles, willowherb, dandelion and bindweed. Also suitable for woody brambles, tree stumps and Ivy.
  • Coverage up to 66sqm per sachet

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