Environment Waikato has granted consent for the herbicide Gallant to be used in the Tairua harbour to eradicate the plant pest Spartina.
The Department of Conservation had applied to discharge the herbicide at a rate of nine litres per hectare into the harbour in the vicinity of the Swampy Stream mouth. Five submissions were received, from Fish and Game New Zealand, Tairua Harbour and Watersheds Protection Society, Waikato District Health Board and residents. Of these two submissions supported the proposal, two were neutral and one submission opposed it.
DoC proposes to discharge herbicide in inter tidal areas where Spartina grows with a surfactant to about 500 square metres of Spartina growing at the stream mouth. The work is likely to take no more than one day to complete with further applications when required.
Submitters were concerned about effects on the Oturu Stream ecosystems, repeat spraying to control re-growth and effects on bird life in the harbour.
The applicant said similar controls had been done in other areas and the herbicide consistently killed from 98 to 100 percent of Spartina in a single application. It would not affect non-target plants such as mangroves or rushes, and the effect on bird life would be taken into consideration.
The Hearing Committee said the spread of Spartina in estuaries in the Waikato was a concern to Environment Waikato and DoC. Spartina poses a potential threat to marine ecosystems therefore a high level of control was appropriate.
Alternative methods had been considered but the herbicide was appropriate due to its effectiveness and minimal environmental effect. The discharge would not have an adverse effect on marine ecosystems and broke down rapidly. The Committee did not consider there was a risk to public safety.
The applicant must undertake environmental monitoring to ensure any adverse effects are minimised. Further conditions include public notification prior to spraying and putting up signs to indicate when and where spraying had occurred.
The Council has already issued a consent for Spartina control using the herbicide in various parts of the Region, including Raglan, Kawhia, Aotea, southern Firth of Thames, Waikawau Bay and Whangapoua Harbour.