By Fiona Anderson, Senior Biodiversity Ranger
“What is that plant that looks like giant rhubarb?”
A decade or so ago the answer may have been “That’s Gunnera (giant or Chilean rhubarb), a South American plant that thrives in our mild wet climate here on the West Coast. Take a cutting – grow one at home, they look great over an ornamental pond”. Today, however the answer has changed to “That’s Gunnera, a South American plant that we’re very concerned about. In fact, we’re having a big push to remove all Gunnera from public and private land on the West Coast”.
Gunnera naturally hails from the wilds of central and southern Chile, in the Argentine Andes and in Patagonia, where it favours humid conditions and inhabits marshy lands, stream and river sides. Described as a charismatic megaphyte (large plant), it has huge leaves, fleshy stems and bizarre looking flowers. It is one of largest leaved herbaceous plants in the world and is truly ancient, having evolved around the time of the dinosaurs, some 150 million years ago.
The plant possesses glands that contain a cyanobacterium which fixes nitrogen, meaning that Gunnera can live in what most plants would consider poor conditions. For example, it can grow in pure gravel where little else would survive, or just a few metres above the high tide line or perched on steep cliffs. Salt spray and howling westerly winds cause only a slight browning around the leaf edges. Hence it has been widely successful as a hardy ornamental garden plant.
So why is it a problem you ask?
In the early years Gunnera quietly existed in people’s gardens around the West Coast. The plant did well since it was growing in a climate similar to its South American home. What’s more, it was growing in a community of completely different plants and animals, unrestrained by competition or browsing. Reproducing via large quantities of seed (thousands of small orange fruit are spread by birds, water or in soil and gravel) it began to spread.
Now patches of Gunnera are cropping up in coastal margins, native forest, stream banks, river beds, roadsides, pasture and vacant lots throughout the West Coast. Plants have even been spotted alongside the West Coast Wilderness Trail, where they presumably arrived in the gravel used to form the track.
Our native plants can’t compete with this large leaved invader and disappear, leaving only the weed!
What can be done to stop the invader?
Gunnera is classed as an unwanted organism under the Biosecurity Act 1997 and is included on the National Pest Plant Accord List (MAF Biosecurity Authority 2001), making selling, propagating or distributing it illegal throughout New Zealand. The West Coast Regional Council has the plant included in its Proposed Pest Plant Management Plan 2016 as a general progressive containment pest, requiring landowners to control Gunnera on their own property.
How can I do to get rid of it?
1. Pull out seedlings (all year round).
2. Dig out individual plants or small patches (all year round). Ensure removal of all rhizome fragments and flower/seedheads and dispose of these at a refuse transfer station.
3. Cut and paint (spring): cut off the leaves and paint the stalk stumps with picloram gel or glyphosate (250ml/L)
4. Spray (full leaf and actively growing): glyphosate (10ml/L knapsack)
It’s time to say goodbye to our old friend Gunnera. It was an unfortunate, but thankfully reversible decision to plant Gunnera in our gardens. We still have time to remove this plant before it fully disperses and smothers our special native plant communities. If you need help removing Gunnera from your property contact the local weedbuster at your nearest Department of Conservation office. Let’s get rid of this weed once and for all!
War on Weeds
Hundreds of invasive weeds are smothering our native forests, wetlands and coastal areas, harming our wildlife and transforming our natural landscapes. Help us fight the War on Weeds.