Kauri dieback, myrtle rust and the fight to protect Kiwi trees

by Jenny Nicholls / 24 November, 2017

Dr Amanda Black.

New thinking in a fight against extinction.

“I turned over the leaf and saw the yellow powder. I knew straight away. I thought, ‘Bugger.’”

Kerikeri nurseryman Tom Lindesay had been admiring a collection of one-year-old pohutukawa plants with his employee Sandy Sievers when she noticed strange patches on growing leaf tips.

“It was a... discolouration. Not as bright as you see on a lot of the photographs they hand out,” Lindesay told North & South. And then they flipped the leaf over. “We both thought the same thing,” said Sievers.

Nurseries had been emailed warning photographs of myrtle rust by the Ministry for Primary Industries. Lindesay emailed back some pictures of his plants. “Then all hell broke out.”

It was May 2, 2017.

The ministry’s first report of myrtle rust, on Raoul Island, is dated April 4, 2017, a mere month earlier. A spokesman downplayed the risk.

“It’s over 1000km to the northeast of Northland and access to the island is controlled,” said Geoff Gwyn, the ministry’s director of readiness and response. “Our focus is to do what we can to protect the unique Raoul Island ecosystem from this disease, and to prevent the further spread of the fungus to mainland New Zealand.”

A few weeks later, Lou Sanson, Department of Conservation director-general, told the Northern Advocate that a third of Raoul Island’s pohutukawa forest had been infected by the fungus, which was “potentially beyond eradication”.

It sounds like something out of a horror movie. Microscopic spores! Pustules and bleeding trunks! Hooded contamination suits! 

Tom Lindesay watched in awe as MPI swarmed over his nursery. They destroyed thousands of plants.

“If this operation has nipped it in the bud in Northland, that would make it worthwhile,” he said.

2017 was a red letter year for our native bush. We have been invaded by plant pathogens too small to see – and they are gaining ground.

One of them reduces kauri to oozing hulks, effectively starving them. This is a Phytophthora, pronounced fy-tof-thora – Greek for “plant destroyer”. We know it as kauri dieback. It is close to, but not quite, a fungus.

The second, more recent invader – myrtle rust – is a fungus. It favours the succulent leaves of young plants, distorting and damaging them so the plant starves or dies of an opportunistic infection. Pohutukawa, kanuka, manuka and rata, as well as commercial species such as eucalyptus, guava and feijoa, are members of the myrtle family, and are all technically at risk.

The fungus, Austropuccinia psidii, is known in other countries by the names of its victims. When it was first discovered in South America, it was called guava rust and eucalyptus rust. In Hawaii, where it infects the ohi’a tree – which looks like rata – it is ohia rust. In Australia, where about 10 per cent of the flora belong to the myrtle family, it is myrtle rust.

The disease is now firmly established along the Aussie eastern seaboard, from Tasmania to Darwin. By April 2016, 350 native Australian species had proved susceptible.

A year later, Dr Andrea Byrom, director of New Zealand’s Biological Heritage National Science Challenge, reported that several plant species of significance to Aboriginal Australians had become extinct. “Critical to the success of any response [in New Zealand] will be a rapid and co-ordinated approach.”

Fast forward to October 2017. Since Sandy Sievers noticed rust in Kerikeri five months earlier, there have been 121 confirmed finds: four in Northland, 78 in Taranaki, 33 in the Bay of Plenty and six in the Waikato.

And it isn’t even summer yet. Myrtle rust loves summer.

Protest signs stand arounda Kauri tree in an attempt to prevent it being felled. Photo by Phil Walter/Getty Images

“The pathogen can sense a kauri tree’s roots, and swim towards them using a tail-like flagella.” - Keep Kauri Standing website 

So does kauri dieback. In August, the Auckland Council threatened to close the 16,000ha Waitakere Ranges Regional Park in a desperate bid to save kauri. The disease is exploding in the park, with almost one in five kauri infected, up from one in 12 six years ago. Most kauri stands in the park now contain infected trees. Kauri dieback (or KD) can be spread by a speck of soil from trampers’ boots or animal hooves, and there is no cure. It is threatening kauri with extinction in the wild.

“The situation is dire for kauri,” says Amanda Black, a senior lecturer at Lincoln University’s Bio-Protection Research Centre who’s at the forefront of New Zealand’s scientific response.

“I’ve seen the bleached stag heads and the bleeding trunks when I’ve gone into Waipoua forest to collect samples for research. There is only one treatment for KD, which is phosphite injections to individual trees. It stops the spread of the disease within the tree – but not between the trees.

“It’s a really sad thing to see. Here is an ancient family, around since the dinosaurs – one of the few connections to Gondwana – now really and truly facing extinction because of a modern biosecurity threat brought in by the nursery trade.

“To local Maori, mana whenua, these are their tupuna, their ancestors, and so it is culturally devastating for them, losing a relative, a loved one.”

Black says Northland kaumatua have extensive knowledge of kauri forests, plants and their properties. With Dr Monica Gerth from the University of Otago, she is exploring the finer mysteries of how KD spreads, and also asking if bioactive chemicals excreted by the roots of other plants might prove protective for kauri.

In 2015, Black helped set up a remarkable organisation to utilise the knowledge and organisational grunt of marae – and allow Maori to collaborate in the fight against invasive plant pathogens.

“There are few of us scientists in this space and we were getting swamped,” she says. “By setting up a network, we can respond collectively, share the load and bounce ideas off each other.”

The Maori Biosecurity Network, now also known as Te Tira Whakamataki (the watchful ones), includes Maori plant pathologists, soil chemists, politicians and iwi leaders. “We have solid relationships with non-Maori researchers and other groups. They like what we’re doing, and we need their skills, so it’s a win-win.”

As well as its work on KD, the network is involved in fighting the wind-borne fungus that Black had long been predicting. “We’d been trying to get funding to prepare for myrtle rust for at least two years,” she says. “When we finally got the okay, it was already here, so we had to act quickly.”

The network was recently given a mandate to speak on behalf of 74 iwi, and regular regional hui are held to find out what communities need. Members post incursion updates on social media and distribute seed-banking kits, made up with the help of the Royal Botanic Gardens at Kew in west London.

“You can look for resistant traits and select for those, although this is not the whole answer for maintaining complex forest ecosystems. But knowing resistance levels – every species has varying resistance within it – allows us to develop strategies.”

There have been no studies of what would happen to our northern forests if kauri became extinct, according to Black. This is “not something that any agency seems to want to fund”.

Kauri are a keystone species. Their longevity and their effect on soil – they make it more acidic – influence the plants that grow around them. They also host co-dependent species such as epiphytes, insects and fungi, so each tree is its own city of genetically diverse life.

“You can’t replace 2000-year-old forests,” Black says. “When we lose our plant heritage, we lose chunks of of our culture, language and history. ” 

This is published in the December 2017 issue of North & South.



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