Imma Perfetto
Cosmos science journalist
Lord Howe Island remains optimistic that it can eradicate the plant pathogen Myrtle Rust which has the potential to devastate the Island’s ecosystems.
Last week the Lord Howe Island Board announced the temporary closure of about 70% of the island to all non-essential visitors, due to the discovery of the fungus (Austropuccinia psidii) that causes the plant disease myrtle rust.
Because the fungal spores are highly transferable, people are barred from entering the Permanent Park Preserve to stop their spread by human activity – the one method of spread that can be controlled for.
Detected on the Island on 3 February, the pathogen has since been identified in three additional locations during subsequent weekly sweeps. Two of these sites are around 230 meters from the PPP boundary.
Lord Howe island describes itself as “Paradise,” and is characterised by subtropical forests, white sandy beaches and crystal clear waters.
What is myrtle fungus and why is it a problem?
Professor Brett Summerell is a mycologist and plant pathologist, and the Chief Scientist and Director Science, Education, and Conservation at the Royal Botanic Garden Sydney. He says that myrtle rust is a major problem in Australia because it effects plants in the family Myrtaceae – a range of species which includes eucalypts, paperbarks, tea trees, and lily pillies.
“Infections in the leaves typically results in a brown lesion on the upper side and yellow spore masses (pustules) on the underside of the leaf – these can coalesce across the whole leaf and kill the leaf and eventually the whole shoot,” he explains.
“The fungus can also attack flowers and developing fruits and kill them, rendering the plant infertile.
“New foliage is most susceptible – so when the tree is actively growing – and especially as the plant might be putting out a new flush of growth after events like bushfires.”
Infections across a whole tree can give it a scorched appearance and lead to its death.
The Lorde Howe Island board says endemic Myrtaceous species, including the iconic mountain rose and scaly bark trees, are dominant in many of the plant communities on theisland.
How did myrtle rust get to Lord Howe Island?
Myrtle rust is thought to have evolved originally in Brazil but has rapidly spread around the globe over the past 70 years. As micro fungus, it produces masses of distinctive yellow spores that are easily dispersed in the wind and can be carried across continents and oceans.
“It arrived in Australia in April 2010, and it’s believed that it hitched a ride, probably on somebody’s clothes, from an infestation in Hawaii,” says Summerell.
“Since 2010, it has spread up and down the east coast of Australia, spread across to Darwin and parts of the Northern Territory, and was first detected in the far end of Western Australia last year.”
Lord Howe Island is 586 kilometres east of Port Macquarie in New South Wales and Summerell says that the most likely scenario to explain its arrival is that spores were blown across from eastern Australia – a fate not unique to the island.
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“Presumably, it’s blown across to New Zealand, and to Lord Howe Island, and some other Pacific Islands, and spread up from here probably into parts of Indonesia and Singapore.”
The New Zealand Ministry for Primary Industries says myrtle rust blew in from Australia after 2010, and after attempts at eradication, it now focusses on managing the situation. “Myrtle rust is now widely found across the North Island and in some areas of the South Island,” says the Primary Industries website.
Can it be eradicated from Lord Howe Island?
Despite New Zealand’s inability to eradicate the rust, the Lord Howe Island Board is asking for the support of the entire community and says eradication is still possible at this stage.
But this isn’t the first time that myrtle rust has been discovered on Lord Howe Island – it was detected in 2016 and efforts put into place at the time effectively eradicated the fungus then.
Summerell also believes it’s possible that it can be done again.
“We have a reasonably good range of fungicides for the control of the disease available for us to use. And those plants that are infected can also be just pulled out and destroyed and either burnt or disposed of in such a way that it’s no longer a source of infection,” he says.
“It does depend on how many plants have been infected and how big an area that’s affected. But I’m optimistic that they should be able to eradicate it.”
According to Summerell, scientists are now starting to have a good understanding of the impact of this particular disease, with about 12-14 species in eastern Australia and rainforest areas badly affected.
“So, it’s really important to get on top of this disease, particularly in places like Lord Howe Island, early, in order to eradicate it, because we know that it can cause the likely extinction of some species, which is what we’re seeing in eastern Australia,” he says.
Summerell also suggests that a critical next step for Lord Howe Island will be to make sure that seed and propagation material of all the species likely to be infected by myrtle rust are collected.
“We can start to build up a population and a collection in seed banks and in Botanic Gardens, so that we have a backup if we need to.”