As much as a third of the pohutukawa forest on Raoul Island is infected with the deadly plant fungus myrtle rust.

The fungus, which can attack pohutukawa and manuka as well as garden plants and crops such as feijoa, was discovered this month in Kerikeri, where a major biosecurity operation is under way to eradicate it.

On Raoul Island, in the New Zealand-administered Kermadec Islands 1100km north of Cape Reinga, however, the disease was found early this year and may already be beyond eradication.

Lou Sanson, the Director-General of Conservation, told the Advocate that a third of the volcanic island's pohutukawa forest was affected by the fungus.

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"It's potentially beyond eradication, and the logistics of eradication on Raoul are very complicated. We can use the Navy ship - we've had superb help from Defence - but we can't take civilian helicopters and we can't put spray booms on Navy helicopters. We have to work all that through," Mr Sanson said.

Department of Conservation staff had been in contact with park staff in Australia and Hawaii, both of which had the disease.

Queensland and New South Wales reported losing some small swamp species but many of the bigger trees, while affected, were not being killed.

In Hawaii, however, their equivalent of the New Zealand rata was suffering badly with many hectares completely dead.

"Unfortunately Raoul Island looks like what happened in Hawaii," Mr Sanson said.

Australian authorities had managed to eradicate the fungus from Lord Howe Island but the French had failed in New Caledonia. In both cases MPI believed the spores had blown out of Queensland.

MPI Director-General Martyn Dunne said if myrtle rust became established in New Zealand it might not be a case of saving the current trees but trying to save the next generation by breeding strains resistant to the disease.

Mr Sanson said cultivars of New Zealand's rarest tree, Bartlett's rata, only 14 of which are known, all in a small area near North Cape, were kept at Dunedin's botanic gardens and seeds of endangered species were being sent to a seedbank in Palmerston North for safekeeping.


Rust found in Taranaki

The plant fungus myrtle rust has been confirmed in Taranaki, the first time it has been found on the New Zealand mainland beyond Kerikeri.

A nursery owner in Waitara spotted the symptoms on Tuesday and called MPI, which confirmed the disease by lab tests yesterday.

MPI incident controller David Yard said the Taranaki property was in lockdown and being sprayed with fungicide. MPI staff had started inspecting all properties within a 500m radius.

"As with Kerikeri, we'll be throwing everything at it to attempt to control it, but we are realistic that it's a huge challenge, given how readily the spores are spread by the wind."

There was no known link between the two nurseries, which had not supplied each other with plants or materials.

Finding myrtle rust in a new region could be a sign that New Zealand had to learn to live the disease, he said.

■ Call 0800 80 99 66 if you think your plants are infected with myrtle rust.