Myrtle rust

Alert

Have you seen myrtle rust?

The presence of myrtle rust can affect the movement of plant products between Australian states and territories.

Find out more about interstate quarantine requirements.

To prevent the spread of myrtle rust in nursery plants, Queensland nurseries can apply to be accredited to issue Plant Health Assurance Certificates for myrtle rust under ICA-42 Operational Procedure (PDF, 788KB).

Be on the lookout for myrtle rust and report it to Biosecurity Queensland. Early detection and reporting are the key elements in controlling myrtle rust.

Call us on 13 25 23.

Myrtle rust is a fungal disease that threatens the nursery and garden, forestry and tea tree oil production industries, as well as natural ecosystems. It affects many plants in the Myrtaceae family, such as gum trees (Eucalyptus), lilly pilly (Syzygium, Acmena, Waterhousea), tea tree and bottle brush (Callistemon, Melaleuca), and guava (Psidium).

Myrtle rust is a new disease to Australia, its full host range remains uncertain. The impact of this disease on native plant communities and associated wildlife in Australia's diverse environments, including some of Queensland's unique and high value native ecosystems, are still unfolding.

Myrtle rust cannot be eradicated because it produces thousands of spores that are easily spread by wind, human activity and animals.

Research is currently focused on understanding the impacts on individual plant species and their communities, to help develop long term and robust management strategies.

In NSW, myrtle rust is listed as a key threatening process. Susceptible hosts such as Rhodomyrtus psidioides, Rhodamnia rubescens and Lenwebbia sp. Main Range have been declared as critically endangered.

Cause

Myrtle rust is a disease caused by the fungus Austropuccinia psidii (formerly Puccinia psidii, initially identified as Uredo rangelii).

Other names

  • Eucalyptus rust
  • Guava rust

Description

Symptoms

  • Myrtle rust causes brown to grey spots, often with a red-purple halo on leaves.
  • Leaf spots can be visible on both leaf surfaces.
  • A few days after infection, masses of bright yellow or orange-yellow spores (powdery specks) appear on the spots surface.

Plant stage and plant parts affected

  • Spots, and subsequent spores, can form on new leaves, shoots, fruits and flowers.
  • New leaves and shoots are more vulnerable.
  • Spots damage plant parts causing deformation, defoliation, dieback and stunted growth.
  • Infection of flowers and fruit can reduce the plants ability to reproduce.
  • Highly susceptible plants may die.

May be confused with

Different types of rust disease can be found on a variety of plant species, however the only rust causing bright yellow or orange coloured spores on Myrtaceae plant leaves is myrtle rust.

Distribution

  • Widespread across Queensland.
  • Mainly along coastal regions east of the Great Dividing Range; especially in areas with mild temperatures and high humidity or high levels of leaf wetness.
  • Limited detections have been made west of the Great Dividing Range.

Hosts

Over 350 species from 58 different genera within the Myrtaceae family.

Plants affected include gum trees (Angophora, Eucalyptus, Corymbia), lilly pilly (Syzygium, Acmena, Waterhousea), bottle brush and tea tree (Callistemon, Melaleuca), brush box (Lophostemon), myrtle (Backhousia) turpentine (Syncarpia), Lenwebbia, Rhodamnia, Rhodomyrtus, Austromyrtus, and guava (Psidium).

Life cycle

The lifecycle of myrtle rust in Australia involves the production of two types of asexual spores.

Summer spores

  • Bright yellow to orange.
  • Produced quickly, in very large numbers and spread the disease to new hosts by wind, animal and people movement.
  • Can survive for a few weeks in suitable conditions, but need to find fresh host tissue quickly to be able to infect.
  • The warm, sunny days with heavy morning dews of spring and autumn in southern Queensland, provide perfect conditions for myrtle rust infection and spread. High humidity and moderate temperatures (night temperatures of 15−25°C) favour spore germination.

Overwintering spores

  • Darker, more robust, and seldom seen.
  • Produced in colder climates, where host plants become dormant or where weather conditions stay below 15°C for prolonged periods.
  • Take longer to produce and longer to germinate in the spring when suitable conditions return. At any time of year:
  • Myrtle rust spores need surface water to germinate, and warm weather to infect plant cells and reproduce.
  • Myrtle rust symptoms (leaf spots and summer spores) can also be more visible when host plants have growth flushes.

At any time of year

  • Myrtle rust spores need surface water to germinate, and warm weather to infect plant cells and reproduce.
  • Myrtle rust symptoms (leaf spots and summer spores) can also be more visible when host plants have growth flushes.

Impacts

  • The long-term impact of myrtle rust is currently not well understood.
  • Myrtaceous plants in Australia have not been exposed to this disease before.
  • Some plant species are highly susceptible and are killed by the disease.
  • Some plant species struggle to reproduce or compete.
  • The disease may have a significant impact on some species, with flow on impacts to Queensland's biodiversity and commercial industries that use myrtaceous plants, such as cut flower, nursery, garden, native forest timber, tea tree oil production and bee keeping.

How it is spread

  • Large numbers of spores are easily spread by wind, human activity and animals.
  • On their own, myrtle rust spores can readily spread the disease over short and medium distances, with occasional long distance spread.
  • Movement of infected plant material can spread the disease over long distances.

Monitoring and action

Monitor Myrtaceae plants for signs of myrtle rust.

If detected, take action to prevent the spread of the disease.

Minimise the spread of myrtle rust:

  • Know what myrtle rust looks like.
  • Avoid contact with infected plants.
  • Do not move infected plant material.
  • Practise good hygiene, come clean, go clean.

Remember, if you come into contact with myrtle rust you can help prevent the spread of the disease by practising good hygiene, such as washing your clothes, hat, footwear, tools/equipment and vehicle before going to another area.

Control

A number of fungicides are registered for the control of myrtle rust. Consult your local garden centre for a list of approved products.

Legal requirements

If you think you have found myrtle rust, you must take all reasonable and practical steps under your control to minimise any associated risks, including limiting further spread. This is called a general biosecurity obligation (GBO).

Further information