Spartina grass on the mudflats of the Taruheru River from the Peel Street Bridge to the Marina boat ramp was sprayed as a trial in January 2024.
By March the sprayed area was dying off and the spartina banks clearly showed slumping and were starting to be broken down and removed by the normal tidal flow.
The use of the herbicide treated the spartina without causing adverse effects on non-target plants, fish or animals.
More information about the pest spartina on our pest and weeds hub
Spartina alterniflora and Spartina anglica are the 2 species of spartina that were introduced and planted in the river (awa) from where it meets the Waimatā awa to where it meets the Mātokitoki awa.
It was planted to stabilise and bind stopbanks that were eroding in the early 1960s and extend areas available for grazing stock.
Spartina is not native to Aotearoa and is an invasive weed which takes over coastal and estuary areas leaving no space for native plants. Its growth within the awa heavily affects physical modification of the waterway and loss of saltmarsh and mudflat habitat for a wide range of important marine life.
Spartina’s ability to form in dense clumps and trap sediment causes the ground level to rise affecting the waterflow, native inhabitants of ecological zones and increasing the risk of flooding
No nesting birds currently use the spartina banks. Manu (bird) surveys were completed before spraying and will continue over time as spartina is replaced by more natural and native habitats. Wading birds do not feed on the spartina as it is not a suitable source food.
Once spartina dies off and the area is returned to mud flats, shellfish and mud crabs will have more habitat to live in, providing a greater source of food for native manu.
*Images for reference.
How long is the project going to take?
We plan to replace spartina over the whole of the Taruheru River in the next few years. After the silt washes away and the mudbank stabilises, we plan to plant native species on the bank.
What will happen after it's sprayed?
We'll monitor and track the impacts of the spartina removal. This will measure the health of the river (awa), species and habitats in comparison to data taken before its removal. The project includes native revegetation of some riparian and salt-marsh areas.
Will it need to be manually removed?
Manual or mechanical removal of root zones runs the risk of the roots being displaced and then taking root somewhere else. The programme is designed so the plant and root zone will die and over time will be washed away by tidal movements within the awa.
Project funding
This trial project coordinated by Haumanu Tū Ora (H2O) is funded through the Freshwater Improvement Fund by The Ministry for Environment and Gisborne District Council. It is a collaborative project between Gisborne District Council and mana whenua focused on improving the urban streams of Tūranganui a Kiwa.