Myrtle rust (Austropuccinia psidii) is also known as guava rust and eucalyptus rust.
The fungus attacks various species of plants in the Myrtaceae family, also known as the myrtle family. It is found in many parts of the world including New Caledonia and all along Australia’s eastern seaboard.
Myrtle rust spores are microscopic and can easily spread across large distances by wind, or via insects, birds, people, or machinery.
The spores are thought to be capable of crossing the Tasman Sea from Australia to New Zealand on wind currents.