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Japanese Knotweed is an aggressive plant that has the ability to destabilize building foundations and destroy sewage and water main infrastructure with its vigorous root growth. Knotweed can colonize large areas with just a small portion, grow up to three metres (10 feet) high in a single growing season, and can out-compete native vegetation. In addition, Japanese Knotweed is listed as a provincial-wide Noxious Weed under BC’s Weed Control Act and Weed Control Regulation.
Controlling Japanese Knotweed requires a long-term commitment. The only control method considered widely effective is the application of herbicide, such as products that contain glyphosate (ex. Round Up). This method involves spraying Japanese Knotweed several times until the roots are killed.
Note: glyphosate cannot be used within 1 metre of a stream, as listed on the product label’s restrictions. In this case, removing the plant by digging out the roots and runners is the only viable option at this time. However, this often involves excavating the soil under and around the plant to a minimum depth of 2 metres and up to 7 metres around. Appropriate disposal of the excavated soil is important and typically involves extremely deep burial (over 5 metres deep) and often must be done on-site; therefore, this method is not commonly used due to challenges and expense involved.
Mechanical methods such as mowing and digging generally are not recommended because they can further spread portions of the plant and stimulate root growth. Cutting may be effective for small areas only if repeated frequently (i.e. once a month) during the growing season, repeating for several years until the roots are dead.
If you find Knotweed on your property, do not compost it in your backyard as it could spread. If you do not want to remove the weed yourself, contact Langley Environmental Partners Society, which may remove the weed for you for a fee and/or give you other options to consider. Learn more about best management practices for knotweed.
To learn more about Japanese Knotweed, visit the websites below:
Japanese Knotweed control strategy
The Township of Langley is working to eradicate the threat of Japanese Knotweed from our roads and parks. You may see markers along various roads in the Township identifying where Japanese Knotweed is located. Do not mow these areas. Improper removal of the plant, such as mowing, could result in Japanese Knotweed multiplying.
The Roads Department is using a mild herbicide spray containing glyphosate to control Japanese Knotweed on road right of ways. The removal process is slow and tricky because it will take several treatments and inspections over the course of several years to ensure the roots are killed. When the roots are dead, the stock of the plant is cut and left on-site to dry. It is then transported offsite and buried up to 5 metres deep in one of the municipal operations storage pits.
In our parks, several patches of Japanese Knotweed have been identified and sprayed with herbicide. All sites designated for treatment are marked with signs indicating the date and type of treatment used. The Parks Department will continue to monitor and spray those areas until the threat of the invasive plant has been eradicated. Areas deemed to be free of knotweed after a number of successive years of no detection will be planted with native species to reduce the likelihood of the area being recolonized by invasive plants.