Myrtle Rust Questions and Answers

8 March 2011

A fungal disease known as Myrtle rust was first detected on a property on the central coast of New South Wales in late April 2010. Myrtle rust has now been detected in numerous locations in Queensland and New South Wales ranging from commercial plant nurseries, public amenities and large areas of bushland.

There are indications that the disease may have been present in Australia for at least two years prior to detection.

The Myrtle rust National Management Group agreed on 22 December 2010 that it is not technically feasible to eradicate this plant disease.  The decision of the National Management Group reflected the difficulty of eradicating and slowing the spread of this disease, increased understanding its behaviour, host range and spread beyond the New South Wales Central Coast to a large number of domestic, commercial, public, recreational and bushland sites.

Due to the potential for Myrtle rust to have an ongoing impact on the natural environment, the community and some key industries, ongoing arrangements to nationally coordinate projects or direct actions to manage the disease have been put in place.

A Myrtle rust Coordination Group, chaired by the Commonwealth, has been established. Technical and policy input is being provided by primary industries and environmental agencies within each jurisdiction, relevant non-government organisations and affected industries. 

The Myrtle rust Coordination Group will consider and coordinate ongoing actions to respond to Myrtle rust focusing on mitigating its impact on the natural environment, including threatened and endangered species and industries that rely on Myrtaceae. These actions will include education and awareness, strategies for industries and collation and analysis of information about the behaviour of the disease and its impacts on natural ecosystems.

Members of the Myrtle rust Coordination Group include representatives of the Australian Government Departments of Agriculture, Fisheries and Forestry and Sustainability, Environment, Water, Population and Communities, representatives of state and territory primary industries and environment departments, Plant Health Australia, A3P, Nursery and Garden Industry Australia, the Institute of Foresters of Australia, the Australasian Plant Pathology Society and the National Association of Forest Industries.  Representatives of other non-government organisations have also been asked to contribute their skills and expertise.

What is Myrtle rust?

It belongs to a group of fungi known as the ‘guava rust complex’. Myrtle rust can affect plants belonging to the family Myrtaceae, which includes many Australian native species including Eucalyptus.

The rust has been identified as Myrtle rust based on the host range seen so far in Australia and the structure of its spores.
Information is continuing to be gathered on its host range under Australian environmental conditions through information gathered during surveillance activities and laboratory-based host testing of a range of important commercial and ecological species of Myrtaceae.

Where did Myrtle rust come from and how did it get here?

Myrtle rust was first detected in Australia on the Central Coast of New South Wales in April 2010.  The fungus that causes Myrtle rust has not been found before in Australia. This complex of diseases is native to South America and is also present in the United States of America (Florida and Hawaii) and Mexico. It is not known how this disease entered Australia, however, rust fungi produce microscopic spores which are easily carried by wind current, on people’s clothing, on plants or on goods that are shipped around the world.

What does it look like?

The fungus causes spots on leaves and stems of susceptible plants. These spots develop masses of orange to yellow powdery spores. The disease most often affects young shoots and the growing tips of plants causing leaves to become curled and distorted and often killing new growth.
More information, along with photographs of host plants can be found on the Department of Industry & Investment NSW website and the Queensland Department of Employment, Economic Development and Innovations website.

Is it the same as eucalyptus/guava rust? 

Myrtle rust and eucalyptus/guava rust are both serious pathogens which could damage Australia’s natural environment and severely impact nursery and forestry industries.
Although both rusts have some morphological differences, preliminary molecular testing indicates they are closely related but has not established the exact nature of the relationship. 
The identity of the disease did not affect the manner in which the initial eradication response was handled as the actions taken were directed at dealing with a high risk incursion.

How is it spread?

The main routs of spread are infected nursery plants and as spores on infested clothing and equipment.

Where has Myrtle rust been found?

Myrtle rust has now spread to numerous locations in New South Wales and Queensland including commercial plant nurseries, public amenities and large areas of bushland. This reflects the difficulties of managing this type of pathogen, despite concerted efforts directed at suppression and eradication.  

Due to the expanding host range of the disease and the increase in the number of locations that Myrtle rust has been detected, further spread of the disease is anticipated. 

What kind of damage can be done?

Little is known about the disease and its impact under Australian conditions and on the wide range of Myrtaceae that grow here. When severely infected, young plants and new growth may become stunted and in the worst case may die.
  
Scientific studies and observations of the disease show that plants can vary greatly in their susceptibility or resistance to the disease. Testing is continuing on a range of Myrtaceae plants to find out which could be hosts so that researchers can assess the potential impact on the Australian environment as well as industries such as Essential Oils and Plant Extracts, Wildflowers and Native Plants, Tea Tree Oil, and forests.

What plants are affected by it?

Surveillance has found evidence of Myrtle rust on these Myrtaceae plants:

• Acmena smithii (lilly pilly)
• Agonis flexuosa (willow myrtle) 'Afterdark', 'Burgundy', 'Jeddas Dream'
• Angophora floribunda (rough-barked apple)
• Austromyrtus dulcis (midgen berry)
• Austromyrtus inophloia (see Gossia inophloia)
• Backhousia citriodora (lemon-scented myrtle)
• Backhousia myrtifolia (grey myrtle)
• Callistemon viminalis (weeping bottlebrush)
• Callistemon salignus (willow bottlebrush)
• Callistemon 'St Mary MacKillop’'
• Chamelaucium uncinatum (Geraldton wax)
• Choricarpia leptopetala (brown myrtle or rusty turpentine)
• Eucalyptus agglomerata (blue-leaved stringybark)
• Eucalyptus deanei (mountain blue gum or Deane's gum)
• Eucalyptus elata (river peppermint gum)
• Eucalyptus pilularis (blackbutt)
• Eugenia reinwardtiana (beach cherry)
• Gossia acmenoides (scrub ironwood)
• Gossia bidwilli (scrub python tree)
• Gossia hillii (scaly myrtle)
• Gossia gonoclada (angle-stemmed myrtle)
• Gossia inophloia 'Aurora' and 'Blushing Beauty' (syn. Austromyrtus inophloia)
• Lenwebbia prominens (southern velvet myrtle)
• Leptospermum petersonii (lemon-scented tea-tree)
• Leptospermum rotundifolium (round-leaved tea tree)
• Lophomyrtus bullata 'Rainbow's End'
• Lophomyrtus x ralphii 'Red Dragon', 'Black Stallion', 'Krinkly'
• Melaleuca alternifolia (tea tree)
• Melaleuca quinquenervia (broad-leaved paperbark) (images)
• Melaleuca linariifolia 'Claret tops'
• Melaleuca nodosa (prickly-leaved paperbark)
• Metrosideros collina 'Tahiti' and 'Fiji'
• Myrtus communis (common myrtle)
• Rhodamnia argentea (silver myrtle)
• Rhodamnia maideniana (smooth scrub turpentine)
• Rhodamnia rubescens (scrub turpentine)
• Rhodamnia sessiliflora (iron malletwood)
• Rhodamnia whiteana (white malletwood)
• Rhodomyrtus psidioides (native guava)
• Syncarpia glomulifera (turpentine)
• Syzygium anisatum (aniseed myrtle)
• Syzygium australe 'Meridian Midget'’
• Syzygium jambos (rose apple)
• Syzygium luehmannii (small-leaved lilly pilly, riberry)
• Syzygium luehmannii x Syzygium wilsonii 'Cascade' (lilly pilly)
• Syzygium oleosum (blue lilly pilly)
• Syzygium paniculatum (brush cherry)
• Syzygium tierneyanum (river cherry)
• Tristania neriifolia (water gum)
• Uromyrtus australis (peach myrtle)
• Uromyrtus lamingtonensis (lamington peach myrtle)
• Xanthostemon chrysanthus (golden penda)

Will Myrtle rust affect me? Will it affect my backyard?
Many popular Myrtaceae garden plants are severely affected by Myrtle rust (eg. Rose Apple, Austromyrtus Blushing Beauty and Aurora).  Gardeners should consult their local nursery for advice on treating rust fungi. A brochure for “managing Myrtle rust in my backyard” is available from the I&I NSW website. If you do see anything that looks like Myrtle rust please report it to the Exotic Plant Pest Hotline on 1800 084 881. In NSW, you should report new hosts in the “red zone” and all new detections in the “green zone”. This number operates across Australia and should be used to report any suspect exotic plant pest or disease. There is no evidence to suggest the disease is harmful to people or to animals.

Is it going to damage the environment?

At present the disease has been recorded in the field on a wide range of hosts including bottle brush, paper bark, eucalypts and lilly pilly. Host testing conducted on hundreds of Australian native plants in overseas trials using the closely related guava rust organism recorded different reactions by similar plants. This indicates that plants of even closely related species, can vary significantly in their susceptibility to these fungi.  The susceptibility of the same species under Australian conditions is untested because the disease was not known to occur in Australia prior to its detection in April 2010.  This makes it difficult, at this time, to gauge precisely how this disease may affect our environment.  However, work is progressing to better understand the impact of this disease in the Australian environment. 

What is being done about it?

Early response activities

• On 30 April 2010, the Myrtle rust National Management Group agreed that while the rust was an Emergency Plant Pest it was not technically feasible to eradicate from Australia. This was based on advice from the Consultative Committee on Emergency Plant Pests (CCEPP). 
  
• Due to the potential implications nationally of the Myrtle rust incursion, the National Biosecurity Committee (comprising representatives of the Commonwealth and State Territories primary industries and environmental departments) was tasked by the National Management Group to develop a national work program for its future management. The National Work program included:
  
• clearly distinguishing Myrtle rust from Eucalyptus rust
• assessing the impacts of Myrtle rust
• undertaking host testing
• determining the host range and possible geographic spread of Myrtle rust
• researching the overseas experience of Myrtle rust
• developing approaches and options for the management of the Myrtle rust; and
• investigating possible domestic quarantine measures/approaches.
  
• NSW also continued local management activities. 
• Since its decision of 30 April 2010 regarding the technical feasibility of eradication, the NMG subsequently observed that the host range of Myrtle rust in Australia was, at that time, more limited than anticipated, with only two cultivars of Agonis flexuosa highly susceptible.
• The NMG also observed that, at that time, there had been limited spread of the disease with no detection of the disease on Eucalyptus and other species of Myrtacae in the natural environment.
• Noting this information, the NMG agreed in late June 2010 to take a risk management approach by enacting the current interim response plan under the Emergency Plant Pest Response Deed
• By August 2010 the sixth infected property was identified.

An interim response plan to respond to Myrtle rust was put in place in July 2010 under the provisions of the Emergency Plant Pest Response Deed - a legally binding agreement between the Australian Government, all state and territory governments, national plant industry body signatories and Plant Health Australia.  The interim response plan contained actions to suppress the spread of the disease with a view to its potential eradication while gaining additional knowledge of its host range and potential impacts, host testing under controlled circumstances, DNA testing, surveillance of known infected properties and the natural environment, tracing movements of plants and other means by which the disease may have spread, destruction of infected host material and ongoing suppression activities at known infected properties.

Through the implementation of actions within the interim response plan, the Myrtle rust National Management Group recognised from the outset that eradication of the disease would be difficult to achieve, as historically, there has been little success in the control of diseases with air-borne spores. While we do not believe that Myrtle rust is able to be eradicated, due to the potential for it to have an ongoing impact on the natural environment ongoing arrangements to nationally coordinate projects directed at understanding the disease’s impacts, and direct actions to attempt to manage the disease have been put in place.

A Myrtle rust Coordination Group, chaired by the Commonwealth, with technical and policy support provided by primary industries and environmental agencies within each state and territory, relevant non-government organisations and affected industries has been established.  The Group is considering and coordinating ongoing actions including education and awareness activities, strategies for industries and government to mitigate the impact of the disease in anticipation of further spread, collation and analysis of information about the behaviour of the disease and its impacts on natural ecosystems.

As projects under these themes commence and results are known, the Myrtle rust Coordination Group continue to update these questions and answers and provide further communication about the management of the disease.

For more information about the Myrtle rust Coordination Group please contact by email.