|Production threat||Environmental threat||Public threat|
Giant gunnera is an invasive large clump-forming herbaceous plant which forms dense patches that exclude virtually all other plants. It has stout rhizomes (large, fleshy underground stems) and massive umbrella-sized leaves. Overall the plant resembles a giant common rhubarb plant. The plant grows vigorously during spring and early summer, forming new stems, leaves and up to five yellow flower spikes which rise from the base of the leaves. G.manicata (up to 3m high) is larger than G.tinctoria (up to 2m high).
Giant gunnera was introduced to New Zealand from South America for its interesting form and now has moved from the garden to the wild. Giant gunnera can shade out other plants and take over whole areas of both native habitat and pasture land. In the Taranaki region it has aggressively invaded a number of areas, forming dense stands and spreading to bluffs,wet cliffs and several waterways. In the Waikato this plant is showing the same pattern as Taranaki, so acting sooner rather than later to remove and control this pest plant will help us to avoid a similar spread happening here.
Giant hogweed (Heracleum mantegazzianum) looks similar to (but should not be confused with) giant gunnera. Giant hogweed’s leaves are more deeply lobed. It has tall flower stalks with large umbrella-like clusters of greenish-white flowers.
All landowners/occupiers in the Waikato are responsible for the control of giant gunnera on their property. All landowners/occupiers in the Waikato are responsible for controlling giant gunnera on their properties. Giant gunnera is also banned from being sold, propagated, distributed or included with commercial displays.
Pull out seedlings and dig out individual plants or small patches, ensuring all rhizome fragments, flower heads and seed heads are removed and disposed of at a refuse transfer station.
For small patches, dig out, taking care to get all root parts OR cut right back and treat the stumps with a concentrated herbicide in gel form. Bury discarded seed heads and rhizomes deeply or take them to a landfill. Other parts can be composted.
For large patches, cut the plant right down to 10-20cm stumps then apply herbicide concentrate (see summary of herbicides). Repeat in the following season where necessary.
For large patches, cut off the flower heads to prevent further seed dispersal and then spray the leaves well while in full foliage with a herbicide (see summary of herbicides).
|Triclopyr plus penetrant||Cut stump treatment, spray application.|
|Triclopyr/picloram mix plus penetrant||Cut stump treatment, spray application.|
|Metsulfuron plus penetrant||Cut stump treatment, spray application.|
|Glyphosate plus penetrant||Cut stump treatment, spray application.|
|Glyphosate gel||Cut stump treatment.|
|Picloram gel||Cut stump treatment.|
|Herbicide rules will apply. You may need to notify neighbours if spraying. The Waikato Regional Plan explains the agrichemical (herbicides) use rule in section 6.2|
|If applying herbicide over water, a resource consent may be required. Please check with Waikato Regional Council before you begin.|
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