Knotweed

Knotweed is a very aggressive weed with bright green leaves and small, off-white flowers. It outcompetes native plants and has tough shoots and roots that can break through gravel, tarmac, and concrete.

Description

• Asiatic knotweed: one to two metres tall with zig-zagging hairless, blueish to reddish stems.
• Giant knotweed: two to four metres tall with hairless green stems.
• Bohemian knotweed (Asiatic x giant knotweed hybrid):

  two to five metres tall, with bamboo like hollow stems. Stems are mottled reddish brown appearing darker at the nodes. Commonly misidentified as giant knotweed.

• Knotweed is deciduous, dying back to the root base every winter.

• Flowers are small and off-white or greenish, flowering between November and April.

• Leaves are triangular/heart shaped and very large, up to 40cm long.

• Seeds are glossy and brown.

• Generally, knotweed has vegetative dispersal from rhizomes (underground shoots). Asiatic knotweed (Fallopia japonica) also spreads via seeds.

• Dislodged rhizome fragments can spread via floods and drain cleaning machinery, enabling them to rapidly colonise new areas.

• Habitats include along waterways, open areas, gardens, forest margins, roadsides, and wastelands.

What you need to know

Knotweed can grow very quickly into large infestations, outcompeting other plants and preventing seedlings from establishing.

Their tough shoots and roots can break through hard structures like gravel, tarmac, and concrete, causing damage to foundations, paving and roads, and flood prevention structures.

It has the potential to narrow waterway channels, impede water flow leading to siltation, and impact on recreational values of waterways.

Management approach

This is a declared pest managed under the Canterbury Regional Management Plan 2018 – 2038 (PDF file, 10.6MB) within the eradication programme.

Eradication

Pests in the eradication programme are present in low numbers or have limited distribution within Waitaha/Canterbury and eradication is feasible.

The community should make us aware of any knotweed plants in Waitaha/Canterbury. We will work with affected landowners to undertake control of knotweed.

Knotweed is also declared an unwanted organism by Ministry for Primary Industries (MPI).

An unwanted organism is an organism classified as a pest by MPI because it is capable of causing harm to the natural environment, physical resources or human health in Aotearoa/New Zealand.

These species pose a high risk to our environment, economy, recreation, and cultural values.

Rules

Any species declared a pest cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, multiplied, communicated, released, caused to be released, or otherwise spread.

Control

Do not attempt to undertake control of knotweed yourself. Report any sightings to us.