How to control Japanese knotweed?

Japanese knotweed is a perennial grass, with an average height of 3 to 2.5 meters. The leaves are green in color and have small greenish-white flowers in late summer. The Japanese knotweed belongs to the buckwheat family, which does well in sunny and humid areas, such as dikes, roadsides, lawns, and gardens. It generally does well in areas affected by man, which receive a lot of sunlight and crumbling soil for its invasive roots.

Japanese knotweed

If you try to eradicate this weed, you will know its properties are similar to those of Godzilla. The Japanese knot is so resistant that it is known to grow in solid masonry foundations. 

There are several ways to remove this plant, and it sometimes takes several attacks to eradicate it. Getting rid of this weed is not easy, but fortunately, the detailed guide below provides you with various methods of Japanese knotweed control.

Herbicide- Foliar Spray

Whether you use a small handheld, backpack, or large sprayer, spraying the leaves with a herbicide is one way to apply weed killers. There is a relatively high risk of drift during the bath; the pesticide can settle in the surrounding soil, water, or desired plants if you do not take proper precautions. 

As a general rule, the faster the application method, the more it reaches non-target areas. Herbicides with the active ingredients glyphosate, Triclopyr, 2,4-D, Picloram (Tordon), and Imazapyr have shown different effects in the fight against Japanese knotweed individually or in combination. However, they all have potential benefits and risks.

Mixing Weed Killers

When mixing weed killers, ensure you follow mixing precautions and instructions on the product label. Use at least the personal protective equipment you require as indicated on the label, including safety glasses, chemical-resistant long sleeves, and gloves, especially when handling a concentrated herbicide. The usual mixing order for most herbicides for use in aggressive knotweed management is to add half the amount of water to the spray tank, add a measured amount of herbicides, and add all and surfactants, then the rest of the water.

Mix well but thoroughly between steps and once you mix the weed killers, follow the instructions on the label to distribute to the leaves. As a rule, spray enough solution so that the leaves and stems are wet without dripping. Try spreading the top of the leaves and the stem of each plant. It may take several weeks for the plant to show significant side effects. Don’t worry and come back; the best management will go little by little. Check back afterward in the season and again in the following season to see if you need additional treatments.

Herbicide- Cut Stem Wick Applications

This method targets herbicides’ direct application to the plant’s tissue, usually with a sponge or brush. Although this approach is slow, it significantly reduces or eliminates deviation. This method can be useful in areas where factories are, or susceptible areas, or landowners who worry about spraying. Unfortunately, the technique is generally low because there are no more repetitive applications. Apply glyphosate or another herbicide to the stem cavity about 5 cm above the ground between the lowest knotweeds.

Using different herbicides, you can apply different concentrations of solutions using this method. The TNC had partial weed control, although you can use several small areas with a sponge or spatula and 33-50% herbicides. Applying a little amount of concentrated herbicide to the stem cavity with an arm spray and the cut surface appears to work better than using a wick to apply because the plant will absorb more herbicides. Additional treatment of the leaves or wick may be necessary to control new plants and buds.

Herbicide – Stem Injection

The injection of a herbicide of high concentration directly into the cavities of the lower nodes of the trunk of Japanese knotweed plants is a promising experimental method. Although this takes some time, this approach eliminates drift and offers complete treatment control, spraying a herbicide on each stem’s specific group. Because injecting is slower than spraying, in some large and easily accessible areas, especially those away from water, you can more effectively treat with a foliar spray or integration of foliar weed killer injection.

Cultural Control

You can consider the cultivation method as an indirect or preventive weed control method. An example of growing bare grass is to prevent rhizomes from spreading to the ground and excavation equipment. Encouraging or creating alternative ground surface cover offers competition for the knotweed and increases other treatments’ effectiveness. Nevertheless, Japanese grass seems to prevent the growth of other plants.

 In Japanese experiments to control monoculture knotweed growth, only a few weed species appear to live in an old Japanese knotweed area in the next growing season. The giant knotweed seems to cause fewer blockages, and we could grow these areas with fresh grass from the season. When replanting areas with wrinkled grass treatment, you can use herbicides that damage Japanese knotweed but do not damage the grass.

Cut by Hand

Cut the stems to the soil, pruning them whenever possible with scissors or from the soil surface, at least every 2-3 weeks in April or immediately the plant appears until August. The sprouting reduces after August, so you may want to decrease the cut density, but avoid plants larger than 6 inches. Stack the cut stalks where they will dry quickly.


Use herbicides or scissors to cut the grass as often and as low as possible, at least every 2-3 weeks until the end of August. Be careful not to spread stems or pieces of roots on damp soil or water. There are reports of goats eating the knotweed, and, in certain circumstances, controlled grazing of goats may be an option similar to heavy cutting. Note that they also eat desirable vegetation.


If the knotweed forms in soft soil or even better in the sand, pull the plant and large rhizomes through the root canal to remove the root system as much as you can. Although this almost certainly does not kill the Japanese knotweed in one treatment, it reduces the root mass. Whenever you see new growth, start looking for new roots at least 6 feet from the original plant a week after pulling and digging, including seeds, and then try to uproot as many bases as possible at a time. It is probably only possible with small patches. Once you complete digging, dispose of all root material carefully.


When you use this method alone, tilling, or physically altering the root system provides no control and creates many shoots. However, this approach can offer some advantages in an integrated strategy, as it increases the rate of subsequent disruptions.


First, cut the stems from the soil surface and possibly continue tilling. Cover the ground entirely with thick black plastic or several cardboard layers that extend to the bottom of the plant and have at least 2 feet (preferably 7 feet) from the outside of the outer stems. Apply weight to the roofing material and observe the circumference to ensure that no new material appears outside the roofing material. Experiment early in the year or after cutting the plant several times in the spring and reducing its rapid growth. It is essential to leave the Japanese knotweed with the covering for a whole growing season.

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