Chilean rhubarb

Common name: Chilean rhubarb or Giant rhubarb
Botanical name: Gunnera tinctoria 
Management programme: Sustained control - Rule 5a applies

Originates from Chile and Argentina. Introduced to New Zealand as an ornamental garden plant and naturalised in 1968. It looks similar to rhubarb but is unrelated. Gunnera species are known for their symbiotic relationships with cyanobacteria. The blue-green algae Nostoc is found in the root nodes where it fixes nitrogen into the soil.

Why is it a pest?

• Chilean rhubarb forms dense colonies with large leaves shading out and suppressing native vegetation.
• It can eventually dominate stream and lake margins.
• It produces an abundance of viable seed, approximately 250,000 seeds in a year. Seeds are spread by water and birds, and remain viable for 2-3 years.

Where is it found?

• Is generally found in gardens and along swampy areas, roadsides, lake edges and streams.
• Chilean rhubarb can also spread vegetatively by growth of rhizomes and regrowth from rhizome fragments.
• It is found scattered throughout New Zealand but mostly in areas of high rainfall such as Taranaki, where over 40km of coastline is badly infested.
• Has been noted throughout the Bay of Plenty.

What does it look like?

• A giant rhubarb-like herb up to 2m.
• Massive, rough, and wrinkled umbrella sized leaves (80cm x 1m) on sturdy stalks up to 2.5m tall and have 5–7 lobes with raised veins beneath.
• Both leaves and leaf stalks are covered in rubbery red prickles.
• The inflorescence is a spike of 50-75cm, up to 10cm in diameter, bearing very small flowers.
• Flowers October/November.

What are the rules?

Sustained control

Sustained Control pests are well established in the region and preventing the spread is no longer a realistic objective. Management focuses on reducing general impacts of the pest. Landowners/occupiers are responsible for the control of these pest species on their land. Council may enforce control.

Under rule 5a of the RPMP landowners/occupiers must destroy this pest if required by a written direction from an authorised person unless a property specific pest management agreement has been agreed and signed between the occupier and the Council.

Criteria to meet Rule 5A include when the species is being actively managed by council, other agency and or community group, on an adjacent property. See the Regional Pest Management Plan 2020-2030 rules for Sustained control pests for more information.

How do you get rid of it?

Recommended:

1. Small plants can be dug out, taking care to remove all of the larger roots and rhizomes, dispose of these carefully.
2. Spray in spring when the leaves are young and soft with herbicide (Note: Do not spray over water).
3. Cut and paint over leaf and flower stems with herbicide gel.

Dispose of any plant and root material at the refuse station in general waste. Continue treating new growth and pulling seedlings as they appear.

CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and directions for the purchase, use and storage of the product, are followed and adhered to.

Read more on pest control advice, information and regulations.