Scientists have found proof to back up the theory the myrtle rust fungus could have blown over from Australia.
Myrtle rust has now been found at 29 sites in Northland, Taranaki and Waikato.
myrtle rust Photo: supplied
Ministry for Primary Industries spokesperson David Yard told Morning Report scientists at NIWA have identified up to six weather events that could have brought the fungal spores over from Australia.
Mr Yard said that theory is also supported by a recent finding of significant myrtle rust symptoms in the upper branches of mature trees.
"It's important to realise that if it is, as we postulate, spores being carried over from Australia, then they won't just be in two localised areas.
"As the numbers of cases develop, we will have to review what we do, because it may not be feasible just to go in and pull out plants."
Mr Yard says they are proposing to move to a long-term management solution.
Department of Conservation staff are collecting seeds because of the serious threat of extinction posed by the fungus, he said.
Listen to MPI Incident Controller David Yard