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Japanese Knotweed

Japanese knotweed is an invasive perennial plant that spreads by rhizomes, which can extend up to 3 metres deep and 20 metres wide. It’s a large clump-forming plant, which grows up to 3 metres tall, with light green shield-shaped leaves.

Four species of invasive knotweeds are found in the Metro Vancouver region: Japanese knotweed, Bohemian knotweed, Giant knotweed, and Himalayan knotweed.

Japanese, Bohemian, Giant, and Himalayan knotweeds are classed as noxious weeds within all regions of the province under the BC Weed Control Act.

Why is it a problem?

Japanese knotweed grows rapidly and can quickly overtake native plant species. Its extensive root systems can cause damage to buildings, roads, and other infrastructure.

Furthermore, Japanese knotweed is difficult to eradicate once it has become established, as it can regenerate from small fragments of its root system. Improper handling can unintentionally spread the plant, worsening the problem.

Japanese knotweed is a major concern for property owners, as its presence can reduce the value of land. It is also a concern for local authorities, who have to manage the costs of controlling its spread and preventing its impact on the environment.

How do you Identify Japanese Knotweed?

The appearance of Japanese knotweed changes with the seasons, so it is important to consider the time of year when identifying the plant. Japanese knotweed is most easily identified during the spring and summer months. Key traits of Japanese knotweed are;

  • Red shoots emerge in spring that look like asparagus.
  • Leaves which are shield or shovel-shaped.
  • Stems that resemble bamboo canes with purple speckles.
  • Small, cream-coloured flowers developing towards the end of summer.

During autumn, the leaves will start to go yellow and wilt as winter approaches. The stems will change to a darker brown before the plant becomes dormant in winter.

Frequently Asked Questions

Below is a list of the most common questions we receive about Japanese Knotweed. Don’t see your question? Contact us for more information!

How do you identify knotweed?

  • Red shoots resembling asparagus emerge in the Spring.
  • Leaves are shield or shovel-shaped.
  • Stems resemble bamboo canes and may have purple speckles.
  • Small, cream-colored flowers develop towards the end of Summer.

Not sure if you have Japanese Knotweed? Click here to contact us. Choose “Japanese Knotweed” from the “Services” drop down and then send us a picture. We’ll review it and follow up with you.

How invasive is Japanese knotweed?

Japanese knotweed is highly invasive and can quickly spread through fragmentation, outcompeting native vegetation and causing damage to infrastructure and property. Its vigorous growth and extensive root system make it difficult to eradicate once established. The rhizomes of Japanese knotweed can penetrate deep into the soil, sometimes reaching depths of over 2 meters (6 feet).

Are there different species of knotweed?

Four species of invasive knotweeds are found in the Metro Vancouver region: Japanese knotweed, Bohemian knotweed, Giant knotweed, and Himalayan knotweed.

How long does it typically take to eradicate knotweed?

The eradication process varies significantly depending on factors such as the amount and location of the infestation. Typically, it spans 1-4 years. This timeframe is contingent upon various factors including the plant’s establishment, environmental conditions (such as location, soil quality, and weather), and the extent of disruption to the surrounding ecosystem. Our methods are optimized to achieve the shortest possible timeframe for eradication.

What methods are employed to control knotweed?

The most effective method typically involves applying herbicides 2-3 times annually. However, the approach may vary significantly from property to property depending on the extent of infestation. It might be necessary to employ a single treatment method or a combination of different methods. Given the variability of nature and timelines, our Japanese knotweed specialists are trained to consider all factors to achieve the best possible results.

When is the best time to initiate treatment?

For optimal results with spray treatments, the window of effectiveness typically falls between June and October.

Why is it important not to disturb the ground after treatment?

Disturbing the ground after herbicide treatment can potentially spread Japanese knotweed fragments, leading to further infestation. It is recommended that the plant and soil are undisturbed to prevent re-establishment.

Can you physically remove the knotweed?

Physical removal of Japanese knotweed can be a fast and effective option, especially when combined with herbicide treatments. However, it is essential to seek our professional expertise to ensure removal is conducted effectively and safely.

Can you cut knotweed down?

Pulling or cutting the weed from the ground can stimulate the growth of Japanese knotweed. It is recommended to always leave the plant undisturbed during the growing season (April to October). In the winter months when the plant is dormant, you can cut the brown stems and dispose of them into the garbage.

When is it safe to enter the treated area?

During application of herbicide, please keep persons and pets out of the area. It is safe to enter the yard post-treatment. We advise allowing up to 12 hours for the herbicide to fully dry before permitting persons or pets to access the treated area.

Will the treatment adversely affect surrounding vegetation?

Our skilled team employs techniques to minimize any harm to neighboring plants. However, it’s important to acknowledge that proximity to knotweed may present challenges in entirely avoiding off-target damage.

How is the dead plant material disposed of?

Dead stems should be disposed of in the regular garbage bin. It’s crucial not to dispose of them in compost, as this could potentially facilitate the spread of the invasive plant.

What if knotweed is encroaching from a neighbor's property?

If the source of the knotweed is traced back to your neighbor’s yard, we’ll need their permission to administer treatments on their property. Untreated knotweed poses a persistent threat of spreading, but on your property, we can implement effective spray treatments to manage the invasion.

Can knotweed be treated if it's near a water source?

Yes, although we must maintain a minimum 1-meter distance from creeks and water bodies when applying treatments, as required by regulations.

Please note: The information provided herein is intended for general informational purposes only. Client circumstances may vary, and it is recommended to consult us directly before undertaking any actions related to knotweed eradication. The authors and contributors disclaim any liability for the use or interpretation of the information provided in this document. E.&O.

Knotweed Images

The images below are a selection of knotweed plants at different stages and in different environments. However, knotweed can lie dormant in winter and the plant lifecycle can be difficult to identify. Contact us for more information!

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Learn more about how we can help to remove Japanese Knotweed, or contact us to get started today!

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