The Department of Conservation (DOC) is undertaking an operation in Coromandel Harbour to control the spread of the invasive estuary grass weed Spartina.
Work was scheduled to begin at the end of February with aerial spraying from a helicopter, and will be supplemented with back-pack spraying. The project is expected to wrap up in April. Exact timings for the spraying will depend on a patch of clear weather with minimal wind.
Spartina is a salt-tolerant grass which invades mud-flats and threatens the habitats of some migratory birds and shellfish. It is aggressive and needs to be removed, DOC said.
“When it comes to Spartina, ‘do nothing’ is not an option,” DOC Coromandel biodiversity ranger Jamie Carey said.
“If we don’t address this infestation quickly, we’ll lose valuable habitat for our native species.”
The herbicide DOC will be using is halyoxfop-methyl, which affects only grasses and has been shown to reduce spartina by up to 95 per cent with a single application. It is low-risk to humans and breaks down in water, a DOC-issued fact sheet said; however, it is known to be “moderately toxic to some species of fish and invertebrates at high concentrations”.
Jamie said the use of the chemical was closely controlled and monitored by DOC, the Waikato Regional Council, and the Environmental Protection Authority.
“The target weed, Spartina, is sprayed at low tide when there is minimal opportunity for the herbicide to enter standing water and is therefore absorbed into the spartina plants,” he said.
“To date DOC hasn’t recorded any negative ecological impacts, either acute or chronic. Work already undertaken in recent years within the Whitianga district is consistent with this lack of measurable impacts.”
Jamie said monitoring would be undertaken after the operation to ensure water quality in the harbour has not been compromised, as per DOC’s consent to use the product.
“We acknowledge some people do not support the application of herbicide, however it is currently the most efficient and effective method of controlling this weed. The focus of the weed control is to protect our estuaries, native flora and fauna.”
People are advised to avoid fishing and gathering kai moana within 500 metres of the affected areas for five days following spraying. Signs with application dates will be placed in key access locations around the estuary and harbour.
