Myrtle rust 'incredibly difficult to actually eradicate'

6:21 pm on 5 May 2017

The discovery of a new plant disease, myrtle rust, in Northland is being described as devastating, with the potential to damage New Zealand's native trees and economic position.

Myrtle rust can threaten plants including pohutukawa, manuka and feijoa trees.

Myrtle rust can threaten plants including pohutukawa, mānuka and feijoa trees. Photo: Supplied

The Ministry for Primary Industries (MPI) has launched a biosecurity operation in Kerikeri, after a nursery owner found the fungus on his young pohutukawa.

The fungal disease - originally from South America - was discovered on pohutukawa trees on Raoul Island, 1100km north east of New Zealand last month.

MPI said in this country it had the potential to damage pohutukawa, rata, mānuka, gums, bottlebrush, feijoas, guavas, and all other members of the myrtaceae family.

The disease was first detected in Australia in 2010 and has spread throughout the country because eradictation attempts were not fast enough. It has killed large numbers of native trees from Northern Queensland down to Tasmania.

An Australian biosecurity expert said myrtle rust was still affecting trees and plants seven years after it was first detected, and New Zealand needed to act fast.

The chief executive of Australia's Invasive Species Council, Andrew Cox, said the disease needed to be stopped as soon as possible.

The Kerikeri nursery where myrtle rust was detected.

The Kerikeri nursery where myrtle rust was detected. Photo: RNZ / Lois Williams

MPI director of readiness and response Geoff Gywn said the disease had only been found one nursery so far.

He said early detection was the best chance to contain the pathogen and the ministry was currently using fungicide to spray affected trees.

"It's incredibly difficult to actually eradicate this type of fungal disease, there's been no successful attempts internationally.

"We'll be dealing with each particular find based on the circumstances because they are quite variable, what we have now is an early and best opportunity to manage this disease."

Mr Gwyn said it had always been a matter of when, not if, the wind-borne spores would reach New Zealand, and the ministry had been preparing for it.

It had 1400 surveillance sites around the country and had been working closely with the Nurserymen's Association and the Department of Conservation (DOC) to raise awareness of the disease.

MPI biosecurity staff have been working at the Kerikeri nursery where myrtle rust was detected.

MPI biosecurity staff have been working at the Kerikeri nursery where myrtle rust was detected. Photo: RNZ / Lois Williams

That meant when a Kerikeri nursery owner spotted the fungus on his young pohutukawa trees on Tuesday night he was pretty sure what it was, Mr Gwyn said.

"He deserves congratulations. It does give us the opportunity to manage this disease at the earliest possible time," he said.

Mr Gwyn said it was hard to predict how myrtle rust might affect New Zealand species: the impact could vary from tree to tree and young trees were more susceptible than old ones.

But potentially at risk were New Zealand's $300 million mānuka honey industry; the $41m eucalyptus timber trade and the fledgling $2m feijoa industry.

Another blow for Northland's native trees

Northland Conservation Board chair Willy Wright said coming on top of kauri dieback disease, myrtle rust was a serious blow.

"The board is devastated and the community will be too, to hear this," he said.

"I mean here we are trying as a priority to deal with kauri dieback ... and now myrtle rust ... it's devastating the potential damage this could do not just to our native trees like pohutukawa and rata and mānuka but to [NZ's] commercial and economic position."

A team of 20 MPI staff arrived in Kerikeri yesterday to lock down the plant production nursery in Riddell Road, spray plants with fungicide and investigate whether myrtle rust has spread.

They have begun contacting all commercial customers who have bought plants from the nursery in recent weeks, and were appealing to any home gardeners who had bought trees from any Kerikeri nursery to check them for signs of disease.

Minister for Primary Industries Nathan Guy said that included feijoa and guava trees.

"Our advice to anyone that's growing feijoas or has purchased any trees, particularly from the myrtle family from this nursery or other nurseries in the Kerikeri region, that they please go out and inspect their trees," he said.

Mr Guy said any sign of disease should be photographed and referred to MPI.

Forests now being checked

Mr Guy and Conservation Minister Maggie Barry are in Kerikeri, meeting with staff from their departments.

Ms Barry said DOC staff were checking myrtle species like rata, mānuka and pohutukawa in nearby forests.

She said the rust appears first as purple pustules on the underside of new leaf growth, then becomes a bright yellow fungus.

Ms Barry said gardeners should not touch it because it was easily disrupted.

"Which is why we are so adamant that people shouldn't touch it, because it is easily spread," she said.

"The Australians admit that their biggest mistake in the early days was allowing too many people through, because they brush against it, and it can be distributed by people, by clothing, by animals inadvertently."

Prominent Northland plantsman Russell Fransham, from Matapouri's Earthsea Gardens, said the prospect of losing coastal pohutukawa was unthinkable.

But while myrtle rust hammered iconic Australian trees when it first landed, in recent years the trees had fought back, he said.

"It was very upsetting [at first], because so many of Australia's native plants are myrtles: eucalypts and bottlebrushes and so on. But now there's very little evidence of it. It seems to have worked out very quickly in a matter of six or seven years. Lots of fatalities, lots of damage but the resistant plants are now in charge and they seem to be showing barely any evidence of the disease."

MPI said myrtle rust could survive over a large part of the North Island, and parts of Canterbury's east coast if its spread proves uncontrollable.

It's advising people to call its pest hotline 0800 80 99 66 for further advice.

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