Myrtle rust, caused by the fungus Puccinia psidii, was first discovered in Australia in April 2010 in a New South Wales nursery. It has now been detected in Queensland, Victoria, Tasmania and the Northern Territory.
Ongoing detections have revealed its presence in commercial nurseries, public landscapes and state forests. It is imperative that myrtle rust is prevented from becoming established in Western Australia.
Threat to the landscape
Laboratory trials have shown that a large number of plant species will succumb to this disease, although it is not yet known how climate differences might influence its spread in WA compared to its spread on the eastern seaboard. In a worst case scenario, myrtle rust could devastate forests and other native habitats. Iconic eucalypts such as jarrah, karri, tuart and wandoo are all at risk as well as the WA peppermint tree.
Myrtle rust could also damage eucalyptus or oil mallee plantations, apiculture, the cut native flower trade and the garden industry, and its spread could affect tourism if natural landscapes were badly damaged.
The visual appeal of streetscapes would be greatly reduced, especially where the council has multi-planted one particular tree, such as red-flowering gum, bottlebrush or paperbark, to create a uniform roadside planting. Native trees in streets and parks provide green corridors through suburbia that provide food, shelter and nesting places for wildlife, so their loss could affect local fauna populations.
Certain plants in domestic gardens are vulnerable to myrtle rust. The first detection in NSW involved a purple-leafed cultivar of the WA peppermint tree Agonis flexuosa ‘Afterdark’ - often grown in the home garden as a small feature tree. Some lilly-pillies (Syzygium species) are also susceptible to the disease, as are other favourite ornamental shrubs including Geraldton wax (Chamelaucium uncinatum), Beaufortia, Kunzea, Verticordia and Calothamnus species.
Home gardens could be protected in the event of myrtle rust occurring, because chemicals (copper oxychloride, triforine, mancozeb, tebuconazole and trifloxystrobin) that control the disease are the active ingredients in several readily available sprays. However, chemical control is not a viable option for large-scale landscapes, native forests and other natural ecosystems.
Keeping myrtle rust out of WA
Bush walkers and home gardeners are likely to be the first people to find myrtle rust if it enters WA.
Naturalists are invaluable as “eyes on the ground” but are also those most likely to inadvertently bring this disease into WA.
Wind disperses myrtle rust spores but wind alone is unlikely to carry them across the desert which separates WA from the eastern states. However, the tiny spores are highly transportable and can stick to clothing, hats, footwear, vehicles and equipment. Consequently anyone who visits NSW, Victoria or Queensland and then returns to WA should take the following precautions:
- If travelling by road, shake out floor mats, wash down tyres and check that the vehicle, caravan, trailer and any gardening equipment contain no plant material. Do this before leaving NSW, Victoria or Queensland and do it again before crossing the border back into Western Australia. The reason for performing the first clean-up is that if any spores are accidentally transported even a short distance into other states they could allow myrtle rust to become established further westward and, consequently, begin the spread of the disease towards WA.
- If possible, change into fresh clothing and footwear before re-entering WA and pack away the attire that was worn in NSW and Queensland. Once home, wash everything that was used on the trip.
- Rail and domestic airline passengers are reminded that any plant material or items contaminated by soil are prohibited entry into WA. If friends or relatives from eastern Australia are planning to visit WA please pass on this advice.
Recognising myrtle rust
Myrtle rust produces bright orange to yellow clumps of powdery spores or pustules. The appearance of these spores or pustules on foliage or twigs varies slightly, depending on the species of host plant, so expert identification is needed.
Anyone who finds what they suspect is myrtle rust should ring the Pest and Disease Information Service (PaDIS) on Freecall: 1800 084 881 to report the location. If possible take a photograph and email it to firstname.lastname@example.org.
Symptoms can also be reported through the MyPestGuide reporter app or by making an online report.
Do not take a sample to post to the Pest and Disease Information Service, because snipping off a piece of diseased plant could dislodge the spores and accelerate the local spread of myrtle rust.