Best weed killer for Japanese knotweed in 2021 (review)

Japanese knotweed is one of the world’s worst invasive species. It causes a serious impact on human activities and biological diversity. The plant has a root system and strong growth that can damage buildings, concrete foundations, roads, retaining walls, paving, and even architectural sites.

When you see the weed growing in your home, you need to figure out the most effective way of eliminating it immediately. You can get the job done using organic removal methods, but most of them take time. The best weed killer for Japanese knotweed should be strong enough to pass down to the plant’s rhizome.

Unless the weed killer gets to the rhizome, the plant will regrow. Remember that it is one of the hardest to eliminate from your home. Herbicide treatments can be useful but could take several months to get rid of it completely.

Regardless of the type of product you use, you must ensure to remove every last root of the plant to prevent it from growing back and spreading even further.

Quick overview: Best weed killers for Japanese knotweed

In order to completely eliminate Japanese knotweed from your garden or lawn, these are the best products to use:

Is Japanese knotweed dangerous?

Japanese knotweed is non-toxic. Its young stems are edible as a spring vegetable. However, it can cause some mild skin irritation on contact. The only thing that makes it dangerous is its invasive nature.

If left uncontrolled, it will grow through brick walls and concrete once it finds a weak spot. That can cause untold damage to buildings, foundations, and pavements, especially when it invades your house.

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Choosing the best weed killer for Japanese knotweed

When on the market for a product that can eliminate the Japanese knotweed, consider the following factors:

  • Ingredients: Look for a herbicide that has glyphosate as the active ingredient. However, ensure the glyphosate has a concentration of at least 41% to offer better results.
  • Application: The best way of applying a weed killer for the Japanese knotweed is through spraying. That will ensure the chemical reaches the plant’s rhizomes.
  • Visible results: The product should be fast-reacting and offer visible results within three hours of application.

Make sure to choose the right volume of the weed killer since you want all the Japanese knotweed gone. When you spray lightly, weeds won’t die off completely. On the other hand, if you leave even a few of these weeds, they will grow back quickly.

Full reviews: What is the best weed killer for Japanese knotweed?

Here is a comprehensive review of the best weed killers that we found to permanently get rid of Japanese knotweed.

1. Compare-N-Save 016869 Concentrate Grass and Weed Killer

Compare N-Save 016869 Concentrate Grass and Weed Killer

Compare-N-Save 016869 is a grass and weed killer that contains 41% glyphosate. In a single application, it will help to eliminate the Japanese knotweed and give you visible results within a week.

The product comes in one gallon that is enough to cover an area of up to 25,000 square feet. You can use it in a variety of places, including driveways and walkways, along fences, around flower beds, trees, and shrubs, and in and around fruit and vegetable gardens.

Pros

  • It helps to kill the Japanese knotweed to the root.
  • It becomes rainproof after two hours of application.
  • Can kill over 170 types of weeds.

Cons

  • Its effectiveness reduces when not used for 90 days.
  • Not ideal for spot-spraying on lawns.

If you want a weed killer that will get rid of knotweed permanently to the root, consider purchasing the Compare-N-Save 016869 Grass and Weed Killer.

2. Roundup Ready-To-Use Weed & Grass Killer III

Roundup Ready-To-Use Weed & Grass Killer III

Roundup Ready-To-Use Weed & Grass Killer III is a convenient, no-mix formula that helps to kill the toughest weeds and grasses to the root. It comes in a pump and sprayer that you can apply around vegetable gardens, tree rings, patios, flower beds, and more.

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When you spray on the Japanese knotweed, it will kill the weed to the root and ensure it does not come back. In fact, it is one of the best weed killers if you want faster results.

Pros

  • Weeds absorb it through the leaves to the root to ensure a total kill.
  • It offers a fast and easy way to kill Japanese knotweed.
  • Easy to refill since you do not need to mix or measure to fill your pump.
  • It offers visible results in three hours.

Cons

  • Although the product works well, the applicator itself is not convenient and does not dispense much at a time.

Roundup Ready-to-Use Weed & Grass Killer III is the best spray that kills Japanese knotweed from the leaves to the root. It is easy to use, and you can apply it in a variety of areas.

3. RM43 Total Vegetation Control

RM43 43-Percent Glyphosate Plus Weed Preventer

RM43 is a weed preventer that contains 43% glyphosate. It helps to kill weeds and prevent their re-growth for up to one year. The product comes in a one-gallon container that is enough to treat an area of up to 17,297 square feet.

You can use it to kill Japanese knotweed that has invaded your fence rows, sidewalks, gravel paths, parking areas, driveways, and around barns and farm buildings.

Pros

  • Ideal for total vegetation control or spot control of brush, weeds, and vines.
  • It combines two herbicides and a surfactant for fast reaction and permanent elimination of Japanese knotweed.
  • Rainproof in two hours.
  • It prevents new growth of up to 12 months.

Cons

  • It is expensive compared to similar products.

The advantage of using the RM43 43-Percent Glyphosate Plus Weed Preventer for Japanese knotweed removal is it combines a herbicide and surfactant. That helps to ensure a fast reaction and total elimination of the unwanted plant.

4. Ortho GroundClear Vegetation Killer

Ortho GroundClear Vegetation Killer

Ortho GroundClear is a year-long vegetation killer and one of the best products for eliminating the Japanese knotweed. It has a concentrated formula that kills weeds and prevents their re-growth through a single application. The product is fast-acting and begins to work immediately.

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When you apply it on driveways, gravel areas, sidewalks, rock and desert landscapes, and parking areas, you will see results in three hours.

 Pros

  • It kills tough weeds to the root when used as directed.
  • It is rainproof in one hour.
  • Starts to kill the Japanese knotweed and other grasses in three hours.

Cons

  • It is a basic concentrate that does not contain glyphosate.

As a herbicide, Ortho GroundClear Vegetation Killer1 offers long-lasting results when sprayed on unwanted plants. It is fast-acting and will start to eliminate Japanese knotweed in three hours.

5. Spectracide Weed & Grass Killer Concentrate

Spectracide Weed & Grass Killer Concentrate

Spectracide is a weed and grass killer concentrate that helps to eliminate unwanted plants from the roots.

It is useful for getting rid of Japanese knotweed that has invaded patios, walkways, and driveways. You can spray it around flowers, trees, and shrubs, as well as along fences and foundations.

Pros

  • It will show visible results after three hours of application.
  • Its effectiveness does not wash away even after 15 minutes of rainfall or watering.
  • You can plant new flowers, vegetables, and even trees in the treated area after one day.

Cons

  • Since it is a concentrate, some users might find it challenging to get the ideal mixture.

Although the Spectracide Weed & Grass Killer Concentrate will help to eliminate Japanese knotweed, that will depend on how you mix the concentrate and water.

Which is best?

The best weed killer for Japanese knotweed is one that has glyphosate as the active ingredient. But the concentration of glyphosate should be at least 41%. This will help to eliminate the plant and curtail its re-growth. In our review, we found that Compare-N-Save 016869 and Roundup Ready-To-Use Weed & Grass Killer III gave the best results. In fact, when applied as directed, you will see results after three hours.

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