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Pest alert - Myrtle rust (Puccinia psidii s.l. syn. Uredo rangelii)
Myrtle rust is an incredibly damaging plant disease as it can potentially affect over 1000 species of plants with the family Myrtaceae. It was first detected in commercial nursery properties in New South Wales in April 2010. It has now spread to Queensland and Victoria.
The causal agent of this rust in Australia was initially identified as Uredo rangelii a taxon within the Puccinia psidii sensu lato (s.l.). complex, and given the common name of Myrtle rust. Recent spore collections from the field and laboratory have identified features matching the description of P. psidii sensu stricto (s.s.) the known cause of Eucalypt/Guava rust. Consequently, it was proposed that the name P. psidii s.l. be the most appropriate to use.
The Department of Agriculture and Food WA has implemented interim measures under the Biosecurity and Agriculture Management Act 2007 to minimise the risk of the disease being introduced into WA
Damage
Myrtle rust produces lesions on young, actively growing leaves and shoots, as well as on fruits and sepals. Leaves may become buckled or twisted as a result of infection.
On turpentine and bottlebrush plant species, rust lesions are purple in colour, with masses of bright yellow or orange-yellow spores. Occasionally, they may have dark brown spores. Severe rust disease in young trees may kill shoot tips, causing loss of leaders and a bushy habit.
Puccinia psidii on Agonis flexuosa (WA peppermint) leaves and stems
Puccinia psidii on Syncarpia glomulifera (turpentine) shoots
Images courtesy of Industry and Investment NSW
Threatened species
Myrtle rust is part of a group of rusts that infect the Myrtaceae family of plants, which include many Australian native species such as bottlebrushes and eucalyptus.
It is most likely that the majority of the thousands of species of Myrtaceae found in Australia have the potential to become infected to some degree by P. psidii s.l., although this wide hostrange may not be fully realized in the field. There are many factors required for the disease to develop, such as the presence of actively-growing young shoots, climatic conditions conducive to infection and availability of abundant inoculum.
In Australia, P. psidii s.l. has currently been found on 107 host species in 30 genera during surveys, including species in Angophora, Asteromyrtus, Austromyrtus, Backhousia, Callistemon, Chamelaucium, Choricarpia, Decaspermum, Eucalyptus, Eugenia, Gossia,
Lenwebbia, Leptospermum, Lophomyrtus, Melaleuca, Metrosideros, Myrtus, Pilidiostigma, Rhodamnia, Rhodomyrtus, Ristantia, Stockwellia, Syncarpia, Syzygium, Tristania, Tristaniopsis, Ugni, Uromyrtus and Xanthostemon. Species under cultivation (in nurseries and gardens) that are severely affected include Gossia inophloia, Agonis flexuosa, Syzygium jambos and S. anisatum while species that are severely damaged in native bushland include Rhodamnia rubescens, Rhodomyrtus psidioides, Choricarpia leptopetala and Melaleuca quinquenervia.
Spread
Rusts are highly transportable. The most common dispersal mechanism is via wind, but they may also be dispersed by honey bees who work the spores on leaves. The spores can also be spread via contaminated clothing, infected plant material and insect movement.
Reporting
Any suspect rust noticed on Myrtaceae species should be reported to the:
Exotic Plant Pest Hotline on Freecall 1800 084 881
To limit the spread of the rust Do NOT collect samples for identification and immediately wash any clothes and skin that may have come in contact with the spores.
Further information
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Australian Nursery Industry Myrtle Rust Management Plan 2011 (Nursery and Garden Industry)
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Identification sheet (Plant Health Committee)
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Myrtle rust (Uredo rangelii) detection (Department of Agriculture, Forestry and Fisheries)
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Myrtle rust (Nursery and Garden Industry Australia)
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Myrtle rust (Queensland DPI)
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Myrtle rust (Wildflowers Australia)
- Myrtaceae species resistance to rust caused by Puccinia psidii (Australasian Plant Pathology, 2010, 39, 406-411)
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Myrtle rust - NSW current situation (DPI NSW)
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Quarantine WA import requirements (Department of Agriculture and Food WA)
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Rapidly expanding host range for Puccinia psidii sensu lato in Australia (Springer Publications)
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Tasmania's import restrictions in Myrtaceae imports (DPIW Tasmania)
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Threat specific contingency plan - Guava (eucalyptus) rust Puccinia psidii (Plant Health Australia)
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Uredo rangelii, a taxon in the guava rust complex, newly recorded on Myrtaceae in Australia (Australasian Plant Pathology, 2010, 39, 463-466)
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Uredo rangelii - pathogen of the month (Australasian Plant Pathology Society)