Japanese Knotweed

Fallopia japonica

Description

Herbaceous perennial, tall with bamboo like stems. The characteristic leaves have a pointed end and flat leaf base (see pictures). Plants can grow up to 3 metres tall with masses of white flowers produced throughout summer.

Distribution

Located throughout Great Britain, generally more frequent within urban areas.

Habitat

Natural habitat is volcanic slopes in Japan and tends to prefer urban areas, especially where heavily concreted. Individuals will tolerate a range of habitat types and can lay dormant in soil for years until disturbed when it can re-grow.

Impact

Is able to out-compete native species as well as cause large amounts of damage to built structures. It can be costly to treat due to legislation concerning its removal.

Control and Management

Control and management techniques vary depending on the site and situation. The following information needs to be evaluated for each site.
Chemical:
a. Young plants (under 1 meter): Glyphosate applied by weedwipper or knapsack sprayer – May to June.
b. Mature plants: Glyphosate applied by weedwipper or knapsack sprayer – July to October.
c. Mature plants: Glyphosate applied into a stem using stem- injection applicators – July to October.

Recommended Action

1. Map individuals and populations and share data with LISI.
2. Follow treatment information as above where appropriate. Before work ensure you have all correct licence and certificates for the use of any herbicide or technique being used.
3. Contact your local Borough or LISI for information if required.
4. Monitor the site for re-growth.

Health & Safety Guidance

You must always consider your own and others safety when treating Japanese knotweed.

Further Information

Further information is available in the planning and development section as well as the Great Britain Non-Native Species Secretariat website.