All giant gunnera species and hybrids – including Gunnera manicata and Gunnera tinctoria are plant pests. Giant gunnera species share many of the same features and are commonly mistaken for one another. However, any confusion between these is unimportant because they are all troublesome plants that require the same control measures.

Giant gunnera are giant clump-forming herbaceous perennials with stout horizontal rhizomes. The plants have an exotic tropical appearance. The plant has massive umbrella sized leaves with stems up to two metres tall. The flower stems look like tall red broccoli, with each seed head containing in excess of 80,000 seeds. In severe winter conditions the plant dies down but grows new leaves in spring.

Ecological values, through the suppression of native plants along coastal cliffs, streambanks and wetlands. The large leaves of giant gunnera prevent other plants growing underneath them. Giant gunnera are tolerant of salt spray and a wide range of climatic and soil conditions, therefore they are very invasive.

Giant gunnera can impede water flow through obstruction of drainage channels and wetlands.

You must destroy all adult and juvenile forms of giant gunnera and hybrids on your property.

What is the 'Pest Management Strategy' for Taranaki?

For heavy infestations applying herbicide is the most practical method of control. If you don’t have time to kill or remove the whole plant, at least remove the seed heads to prevent another season’s seeding.

Physical removal: If plants can be dug out, remove the leaves and seed heads first – use a pruning saw. Grub or dig out the rhizomes. Take care not to leave any fragments of the rhizomes, which can regrow. Dispose of the seed heads and rhizomes by deeply burying them, putting into a black bag to rot, wrapping in paper and putting in your rubbish, or by burning.

Use herbicides such as triclopyr, picloram and metsulfuron (eg Escort), although there is no label recommendation (given that this is a relatively new weed) on these herbicides specifying giant gunnera.

Guidance on using herbicides