Knotweed

Knotweed is a weed with bright green leaves and small, off-white flowers. It outcompetes native plants and can have adverse effects on our waterways.

Description

• Asiatic knotweed: 1-2m tall with zig-zagging hairless, blueish to reddish stems. Flowers from December to April.
• Giant knotweed: 2-4m tall with hairless green stems. Flowers from November to April.
• Leaves are bright green, heart to lancet-shaped, alternating, up to 40cm long, pointed and leathery.
• Flowers are small, off-white, and occur in dense, drooping stems less than 6cm long in summer to autumn.
• 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 forms dense thickets, outcompeting other plants and preventing seedling establishment. 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 an unwanted organism regulated under the National Plant Pest Accord.

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.