Gunnera tinctoria

Giant or Chilean Rhubarb

Gunnera plant

Elaine O'Riordan

Clump of Gunnera plants

Elaine O'Riordan

Gunnera flower spike

Elaine O'Riordan

New growth from rhizomes in spring

Elaine O'Riordan

Community Gunnera project in Leenane

John Holms

About

Gunnera tinctoria, also known as Chilean or Giant Rhubarb, is a South American plant that is spreading out of control in the West of Ireland. It is now spreading rapidly in parts of Connemara.

How to recognise it?

Gunnera is an exotic plant that looks completely out of place in Ireland, and you should have no trouble recognising it at all! In summer it grows to about 2 m tall, with huge rhubarb-like leaves and seed-heads in red/orange spikes at the base. In winter it dies back, leaving withered black stumps, leaves and flower heads.

Why is it a problem?

During the spring and summer months, Gunnera forms huge, dense thickets that take over gardens, derelict sites, riverbanks, roadsides, farmland and open countryside. It is unsightly in the scenic Connemara landscape. Along rivers it prevents access for anglers and livestock and can lead to erosion of riverbanks. It can block ditches, colonise productive land and replace valuable wildlife habitat.

How does it spread?

Gunnera has thick, persistent rhizomes (underground stems resembling roots) which can re-grow from even the tiniest fragment. In Ireland it is often spread by the movement of infested soil or rocks, often associated with road building and development. Mature plants can also flower and produce seed, which are transported by birds, water and traffic or in the movement of soil or vegetation.

Legislation

Gunnera is listed on the Third Schedule of the EU Habitats Regulations which makes it an offence under Regulation 49 to plant, disperse, allow or cause to grow this plant in the Republic of Ireland.

Regulation 50 makes it an offence to import, buy, sell, breed, reproduce or propagate, advertise, offer or export for sale, publish a price list, transport or distribute any species on the Third schedule.

A licence may be obtained in certain circumstances to permit these activities.

What can you do?

Don’t spread the weed. If you find Gunnera on your land:
- Do not dig close to the plant or break up the rhizome, as new plants can grow from each fragment
- Do chop the flowers off mature plants in spring/early summer before they go to seed
- Do not dump plant cuttings or soil elsewhere
Spread the word: Inform your friends and neighbours about the problem with Gunnera
Report to National Biodiversity Data Centre http://www.biodiversityireland.ie/projects/invasive-species/submit-sightings/
Control: Use the most suitable method to remove the infestation from your property (see below).

Control

Manual Control

Small plants may be grubbed out if the entire root can be removed. However, digging is not generally recommended for Gunnera, because soil disturbance and fragmentation of the plant may actually encourage the growth of new plants.

Where possible, removing the flowers off mature plants in spring/early summer before they mature can help to prevent them from spreading seed. Cut seed heads should be placed in a thick plastic bag, sealed and allow to rot down on site. This can take several months.

Chemical Control

Herbicides usually provide the best and most cost effective method for Gunnera control. A systemic herbicide that will kill the roots of the plant is needed and a glyphosate based formula is recommended. The weedkiller can be applied in 2 ways:

Foliar spray: Using the manufacturers recommended concentration, leaves should be sprayed until the point of ‘run-off’ i.e well coated but not dripping. Spraying should only be carried out in cool, dry, calm weather.

Cut and paint technique: Leaf stalks should be cut close to the base of the plant and the stumps immediately painted with a 25% solution of glyphosate applied using a brush or sponge. The leaves can be composted or allowed to rot down on site. This method is recommended for sensitive sites such as around waterbodies.

Please take care when using herbicides, and carefully consider your impacts on nearby land or waterways. Read the label carefully, and always use appropriate safety equipment.

Timing

In Ireland, herbicide treatment of Gunnera is most effective when applied in late summer or early autumn, when the plant is vigorous and before the leaves begin to die back. It should take about 3-4 years of annual treatments to clear the worst of the infestation, after which you should perform annual checks to control any new seedlings growth.

Pesticide regulations

All Plant Protection Products should be used in accordance with the product label and with Good Plant Protection Practice as prescribed in the European Communities (Authorization,Placing on the Market, Use and Control of Plant Protection Products) Regulations, 2003 (S.I. No. 83 of 2003). Herbicides/pesticides authorised for professional use may only be used by persons who have completed the prescribed training and hold the relevant specified certificate(s). http://www.pcs.agriculture.gov.ie/sud/