An invasive fungus attacking some of Australia’s most ecologically important tree species has spread Western Australia while it also flourishes in humid conditions along the country’s eastern side, driving a “silent extinction” and prompting urgent calls for a national response.
Experts warn that if the myrtle rust fungus discovered in the eastern Kimberley reaches the state’s biodiversity-rich southwest, the consequences could be catastrophic for these ecosystems.
The site was discovered in a New South Wales nursery in 2010, the fungus – recognizable by its bright yellow spots and rust on leaves – has established itself along the entire east coast and has been detected in every state except South Australia.
One in 2021 study predicted myrtle rust could claim at least 16 rainforest plants within a generation in an extinction event of “unprecedented magnitude”.
The fungus affects plants in the myrtaceae family – a diverse group that includes rainforest species, paperbarks, eucalypts and myrtles. The once widespread native guava has been nearly wiped out by the fungus.
A team led by WA’s Department of Primary Industries discovered the fungus on nine broadleaf and narrowleaf paperbarks in the eastern Kimberley in late June. The exact species of melaleuca affected is not yet known.
The department is investigating tourist hotspots and nurseries, with no new detections so far. The potential impacts were “yet to be determined”, a department spokesman said, but the disease can cause tree death, decay, species loss and compromise ecosystems.
Dr. Louise Shuey, a forest pathologist with Queensland’s Department of Agriculture and Fisheries, traveled to the Kimberley to help with the detection effort.
“Myrtle rust can travel hundreds of kilometers on the wind, which is why it spreads so far,” she said.
The location was sought after modeling pointed to isolated wetland as a likely site spreading from affected plants in the Northern Territory to the east.
Alyssa Martino, a researcher at the University of Sydney, has started testing 25 WA melaleuca species for their susceptibility to the fungus, which originates from South America. The first three tested have shown high susceptibility.
Martino said the rust sent plant species to extinction, so understanding how different plants responded would help conservation efforts.
Shuey said it would be crucial to keep the rust out of Queensland’s biodiversity hotspot in the south-west, as it was the planet’s most diverse area for myrtaceae – with almost half the world’s species.
Bob Makinson, a conservation botanist, coordinated a national action plan – developed voluntarily by concerned scientists and wild plant managers – through the Australian Network for Plant Conservation.
About 350 Australian species have been identified as fungal hosts. Makinson said the myrtaceae in the state’s southwest were intrinsic parts of the ecosystem.
“Many of them are part of the spring wildflower community that attracts tourists from around Australia and the world,” he said.
“If it becomes established there, we are likely to see a large increase in the number of host species and in the number of native species threatened with decline or extinction. It could be a biological disaster.”
The fungus particularly likes moisture and fresh vegetation, and therefore thrives in new growth after rain or bushfire, which means that wet conditions in the east of the country had provided the perfect environment.
The national action plan was finalized in 2020, but has not been formally adopted by the governments.
“While some agencies and researchers are heroically active on it, their efforts need to be expanded, stitched together and better resourced,” Makinson said.
James Trezise, conservation director at the Invasive Species Council, said myrtle rust was driving a “silent extinction” among Australia’s diverse plant life.
“It is clear that the system for dealing with this major environmental threat is not working,” he said.
“Australia already has the sinister title of world leader in mammal extinction. If we don’t strengthen our threat control and biosecurity systems, we may also find ourselves as the world leader in plant eradication.”
Federal Environment Minister Tanya Plibersek agreed a coordinated response was needed and said the government was working to implement a national action plan.
“There has been targeted investment to create a national inventory of myrtle rust susceptible species and deliver specific myrtle rust training to native rangers and landowners in NSW and Queensland,” she said.