Myrtle rust host plants and symptoms

Lophomyrtus leaves with purple-brown bruise-like lesions and yellow

In Victoria myrtle rust (caused by the fungus Austropuccinia psidii) was never found in bushland or the natural environment.

The fungus was identified on 11 genera of Myrtaceae and up to 28 known species or plant varieties. The main Myrtaceae plants infected with myrtle rust were Lophomyrtus x ralphii varieties (especially 'Black Stallion') and Willow myrtle (Agonis flexuosa 'Nana').

These species have dense canopies and are frequently planted as hedges. Their compact growth may have created a microclimate for the fungus to establish and spread.

Some other genera infected with the fungus were:

  • Austromyrtus
  • Backhousia citriodora
  • Callistemon (bottlebrush)
  • Chamelaucium
  • Metrosideros
  • Myrtus
  • Syzygium (lilly pilly, bush cherry and magenta cherry).

Only three Eucalyptus species (E. olida, E. polyanthemos and E. spectatrix) have been found with myrtle rust infections. Infections were mainly on leaves of potted plants and all these plants were destroyed.

Where myrtle rust comes from

The rust was first detected on common guava and lemon scented gum in South America but now is considered a native of South and Central America.

It was first found on the central coast of NSW in April 2010. Hosts infected were Agonis flexuosa 'After Dark', and later A. flexuosa cv 'Burgundy', Callistemon viminalis and Syncarpia glomulifera.

Symptoms of myrtle rust

Myrtle rust attacks young, soft, actively growing:

  • leaves
  • shoot tips
  • stems
  • fruits
  • flowers.

The first sign of infection may be chlorotic spots on leaves and shoots, followed by the production of masses of egg-yolk yellow coloured spores. This will be about 14 days after infection, initially on the underside of the leaf but later on the upper leaf surface.

These lesions often turn red-purple then brown and might be surrounded by a purple margin. Lesions can extend through the leaf.

Old lesions are usually grey and may still contain a few spores

Severe rust disease in young trees can kill shoot tips, causing loss of leaders and a bushy habit.

Plants affected by myrtle rust

All members of the Myrtaceae plant family are potential hosts of myrtle rust, including:

  • gum trees (Eucalyptus)
  • bottlebrush (Callistemon, Melaleuca)
  • tea tree (Leptospermum)
  • lilly pilly (Syzygium, Acmena, Waterhousea)
  • paperbark (Melaleuca)
  • myrtle (Backhousia)
  • guava (Psidium)
  • midgen berry/midyim (Austromyrtus)
  • scrub cherry, rose apple (Syzygium)
  • brush box (Lophostemon)
  • christmas bush (Metrosideros)
  • lophomyrtus (Lophomyrtus)
  • willow myrtle (Agonis)
  • Geraldton wax (Chamelaucium)

How to recognise myrtle rust on common plants

Expand the following for images that show symptoms of myrtle rust infection on a range of Myrtaceae family plants.

+ Expand all- Collapse all

Myrtle rust on strawberry gum (Eucalyptus olida):

Underside of a strawberry gum leaf with an orange-brown lesion and sporesA lesion forming at the join between a strawberry gum leaf and stemSpores on a strawberry gum stem

Myrtle rust on red box (Eucalyptus polyanthemos):

Myrtle rust stains on red box leaves, distinctive red spots with a purple outline

Myrtle rust on bottlebrush (Callistemon):

Set of bottlebrush leaves that have dark red lesions with yellow spores in the centreClose up of a leaf with lesions bleeding together and yellow spores in the centre of each lesion

Callistemon 'Harkness' bottlebrush infested with myrtle rust:

Bottlebrush stem with dark red lesions at the base of the leaves where they meet the stemTip of a bottlebrush leaf with a deep red-brown lesion. The leaf behind it has two very early-stage red spots

Geraldton wax (Chamelaucium uncinatum) infested with myrtle rust:

Geraldton wax with yellow-gold spore growth on its spiny leavesClose up of geraldton wax with yellow-gold spore growth on the leaves

Myrtle rust symptoms on Fiji Christmas bush (Metrosideros collina):

Fiji Christmas bush leaves with dark a red-brown spot that has a small hole in the centre

Myrtle rust spores on lemon-scented myrtle (Backhousia citriodora):

Bright yellow spores on the leaf of a lemon-scented myrtle leafBright yellow spores on the stem at the base of a lemon-scented myrtle leaf

Common myrtle (Myrtus communis) affected by myrtle rust:

Common myrtle leaves with yellow spores growing on flower budsCommon myrtle leaves with yellow spores growing on petals

Myrtle rust spores on lophomyrtus 'Black Stallion':

Lophomyrtus leaves with purple-brown bruise-like lesions and yellow sporesLophomyrtus leaves with purple-brown bruise-like lesions and yellow spores

Myrtle rust spores on Acmena lilly pilly:

Tip of an Acmena lilly pilly leaf covered in yellow spores

Myrtle rust symptoms on Syzygium lilly pilly:

Syzygium lilly pilly leaf with lesion and yellow sporesLarge lesion causing wilt on a Syzygium lilly pilly leaf

Myrtle rust spores on Agonis flexuosa 'After Dark':

Yellow spores on the underside of an Agonis leaf

Myrtle rust on willow myrtle (Agonis flexuosa) (photo courtesy Dr Angus Carnegie © I&I NSW):

Tiny yellow spots down the length of a willow myrtle leaf

Newly formed bright yellow myrtle rust spores on turpentine (Syncarpia glomulifera) (photo courtesy NSW I&I):

Turpentine leaf with a few new dark red spots and yellow spores

Older myrtle rust infection on turpentine (Syncarpia glomulifera) (photo courtesy of NSW I&I). Note that older lesions can be dull yellow or brown to ash in colour and spore masses may have disappeared:

Turpentine leaf with established rust presenting as severe red-brown lesions all over the leaf

Yellow myrtle rust spores appearing on the fruit of beach cherry (Eugenia reinwardtiana) (photo courtesy of Queensland Department of Employment, Economic Development and Innovation):

Beach cherry fruit with yellow spores

Yellow myrtle rust spores appearing on the immature fruit and flower of iron malletwood (Rhodamnia sessiliflora) (photo courtesy of Queensland Department of Employment, Economic Development and Innovation):

Iron malletwood fruit with yellow spores on its young fruit

Myrtle rust spores on mountain ash (Eucalyptus regnans) inoculated under controlled conditions (photo courtesy of Dr Louise Morin, CSIRO Ecosystem Sciences):

Leaf with red-brown spotted infection

Image credits

Willow myrtle (Agonis flexuosa) photo courtesy Dr Angus Carnegie © I&I NSW, and all other images courtesy David Smith, Agriculture Victoria.

Page last updated: 23 Feb 2022