NZ 'may have lost battle' against myrtle rust

Myrtle rust infects the leaves of myrtle plants and it can be identified from its distinctive rust-like spots with yellow pustules. Photo / File

New Zealand may have "lost the battle" in beating myrtle rust, a top scientist fears, and the official leading the response against the serious plant disease says we could be facing the loss of some vulnerable species.

But there's now some hope that manuka, the lifeblood of our $300 million manuka honey industry, could fare better than first thought against the wind-blown scourge.

Myrtle rust is a fungus that attacks and can seriously affect myrtle species plants, including some significant natives such as pohutukawa, manuka, kanuka and rata.

First found in a Kerikeri nursery in May, it has now been confirmed at more than 100 locations across Taranaki, Te Puke, Waikato, Northland, and, most recently, Auckland and Wellington.

Authorities have met the threat with a large biosecurity response involving 100 people on the ground and millions of dollars in new research.

The coming warmer summer months, offering ideal conditions for spread, would prove crucial for the fight.

Landcare Research scientist Dr Andrea Byrom feared efforts may be doomed.

"It doesn't mean we shouldn't be having as good a crack at it as we can, because it hasn't been detected in natural ecosystems yet, so there is still hope," she said.

"But the reality is, given where in the country it's been found so far, we may have lost that battle."

Ministry for Primary Industries (MPI) incident controller Catherine Duthie said the incursion had been unfolding at a rate that was expected.

"We've had quite a lot of modelling done where we've looked at the plume of spores coming across from Australia, and Auckland and Wellington were the sorts of areas that were predicted to be hit."

It wasn't yet clear how bad the situation could get.

One assessment produced by the Government in 2011 warned large areas of the country could be affected and, at one extreme, some species could die on a "landscape scale", as had happened in other countries.

In Australia, the fungus has had different levels of impact on myrtle species and has caused the extinction of several treasured plant species of significance to Aboriginal Australians.

"The worst-case scenario is we may lose some particularly vulnerable species like Bartlett's rata, particularly as they exist in the wild and because there's only a few individuals left," Duthie said.

"What we are thinking is there's likely to be genetic diversity within populations where some species will be resistant — and of course, there will be less impacts in the cooler regions of the country.

"But it's absolutely too early to tell at this point, and next year at this time it also might be too early to tell — the Australians have been dealing with it for almost a decade and they are still learning."

Authorities have met the threat with a large biosecurity response involving 100 people on the ground and millions of dollars in new research. Photo / File

An incursion the like of myrtle rust had never been seen before in New Zealand.

"This is unusual for rust, in that it impacts multiple species — rusts are usually very specific — so it's unprecedented."

Its eventual detection triggered an eleventh-hour seed-banking effort around the country, with the Department of Conservation directing hundreds of officials to collect seeds of more than 30 native plant species.

Although there were some positive signs for manuka.

To date, officials had searched more than 8500 individual manuka plants and only turned up one infected plant.

"And also the evidence from Australia indicates that manuka is not the right tree to be susceptible, so we might get lucky on that one."

But Byrom pointed out manuka was an incredibly abundant species that was being planted in its hundreds of thousands around the country.

"So it's sort of like looking for a needle in a haystack and that's why surveillance is so important."

Byrom directs the collaborative Biological Heritage National Science Challenge, which, shortly before myrtle rust hit, had funded a multidisciplinary research project aimed at boosting the preparedness of New Zealand's biosecurity system for an incursion of the pathogen.

Alongside other work under the challenge, including a Maori-led response, researchers at Plant and Food Research and Scion are investigating the susceptibility of key species, attempting to store germplasm of myrtle species and developing detection systems to be used in the field.

There's hope that manuka, the lifeblood of our $300 million manuka honey industry, could fare better than first thought against the wind-blown scourge. Photo / File

Overseas, scientists were looking at how New Zealand species in South Africa had fared with myrtle rust.

While the MPI has stated it had long had a "well structured and rehearsed" system for biosecurity incursions like myrtle rust, the Herald is aware of frustration among scientists, with some questioning why a specific strategy wasn't put in place when the disease was first found in Australia in 2010.

"We should be planning ahead — and we should have planned further ahead," said Byrom, who was concerned the work and funding for it had come too late.

She was also worried authorities weren't making the best of surveillance information, and that expertise wasn't being co-ordinated as well as it could be.

"This is one of those situations where there really needs to be a co-ordinated and joined-up response across multiple science organisations, and I think that's been happening, but not as fast as it could have been, and again, that's a bit of a shame."

Anyone believing they have seen myrtle rust on plants in New Zealand were asked to call MPI on 0800 80 99 66.

It was important for people not to touch the plants or attempt to collect samples as this would spread the disease.

Pohutukawa are among species threatened by myrtle rust. Photo / File

People could also check for and report myrtle rust using the just-launched bilingual Myrtle Rust Reporter smartphone app.

WHAT IS MYRTLE RUST?

Myrtle rust (Austropuccinia psidii) has an origin as a tropical-sub tropical fungal disease of the Myrtaceae family (guava, feijoas, rata, pohutukawa, manuka) that "jumped" host range from natural Myrtaceae to planted Eucalypt forests in South and Central America and has spread primarily through biosecurity incursions.

It infects the leaves of the plants and it can be identified from its distinctive rust-like spots with yellow pustules.

Myrtle rust can distort the leaves of the plants, affecting function, but more devastatingly, it makes the plant susceptible to secondary infections within days of the primary rust infection.

It's primarily a wind-borne pathogen that has been helped along considerably through global movement of people and plants, particularly via the nursery trade.

On average one to two exotic windborne fungal rusts per annum have arrived autonomously in New Zealand from Australia since 1952.

New Zealand climate and environment is very favourable: we are subject to strong prevailing westerly weather systems, and have close economic and travel ties with Australia.

Given this and increasing cyclonic events that have been attributed to climate change, myrtle rust likely was blown here during one of these weather events.