Action was taken quickly to try to prevent it's spread: a quarantine area was established around the property; affected plants were sprayed with a fungicide, before being removed and destroyed; movements of people and plants to and from neighbouring properties were traced; a surveillance program was put in place; properties approved to import plants in the family Myrtaceae were investigated, but no signs of disease were detected.
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| Myrtle rust on a Melaleuca paperbark (courtesy of the DPI) |
It is still not known how the pathogen entered Australia, but it is thought that spores may have been carried on clothing and investigations involving the vacuming of the clothing of arriving international passengers has since confirmed the likelihood of this.
Initially, it was thought that the measures taken were enough to control the spread, however by late December 2010, 116 separate infection sites, including in bushland and forest in NSW, had been discovered.
At this point, tests on the fungal spores that had been collected showed that the pathogen had been present in Australia for at least 2 years, indicating that the initial discovery point was unlikely to be the entry point.
The presence of infection in tall forest trees was impossible to treat. The two options open, chemical spraying by helicopter or sterilising through fire, were unworkable due to the presence of water catchments in the affected areas and the possibility of down-drafts and thermal currents further spreading spores.
The pathogen could therefore not be controlled or eradicated.
Since initial infection in April 2010, the pathogen has now spread throughout coastal areas of NSW, south-eastern and central Queensland and, by January 2012, had entered Victoria.
Myrtle Rust belongs to a group of fungi known as the "guava rust complex". This means although it isn't the same fungus that causes guava rust, it is genetically similar. The minimum effect of Myrtle Rust on the environment would be slowing the recovery and regeneration of forests after bushfire or harvesting, but at in worst cases the host plant will die and therefore we could be looking at a change in forest biodiversity in some areas.
However, it is important to bear in mind that we simply do not know yet what affect Myrtle Rust will have on Australia's flora. This is partly because we do not know it's history in Australia, but also because even closely related species are known to be affected differently by the fungus.
Around 150 different species have so far been found to be infected. A list of all plants that could be affected, here and some images showing the differing appearances on different species can be found here.
In Victoria, it was believed that the most susceptible areas for Myrtle Rust infection are the Gippsland coasts and the Otways. However, of the 52 sites in Victoria where infection has been found, these are mostly in the vicinity of Melbourne - including here in the Dandenong Ranges.
Although these are mainly at production nurseries, where of course there are many young, vulnerable plants in close proximity and being regularly watered, there are also around 23 sites on private land.
Update 09/05/2012: I know from a City of Casey employee that Myrtle Rust has been found in the Wilson Botanic Gardens in Berwick. This was quite a surprise to them and it's not sure how long the site has been affected. The infection was picked up by an employee who had just attended a Myrtle Rust awareness course, which really goes to emphasise the importance of these courses in possibly helping prevent the further spread of this disease.
I would urge those in the industry, even volunteers, and also those who spend a lot of time walking in bushland to attend a Myrtle Rust information session. I would also go as far as to suggest that home gardeners, who live in areas that are known to have incidences of infection or where there is a high risk of infection, also attend.
You can find information on Myrtle Rust, and the information sessions, here.
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