Myrtle rust is a particularly damaging and invasive form of rust because it can infect the entire myrtle family, and there are hundreds of known susceptible hosts.
There are many non-native myrtle species in New Zealand, including eucalypts, feijoa, bottlebrushes, lillypilly, and monkey apple. You can use the Myrtle Rust ID Guide or check out the Identify myrtle rust page on this site to help identify myrtles and myrtle rust.
Additionally, Manaaki Whenua – Landcare Research and Biosecurity New Zealand have partnered in the development of the NZ Myrtaceae Key – a free app that makes it easy for citizen biosecurity volunteers to identify susceptible plants and keep an eye out for the fungal disease myrtle rust.
The first visible symptoms are powdery, bright yellow or orange-yellow pustules that develop on leaves, tips and stems. The pustules can progress into wounds on the plant and may cause leaves and shoots to become misshapen or disfigured and die off. The disease can cause deformed leaves, heavy leaf loss from branches, damaged fruits, canopy dieback, stunted plant growth, and eventually may lead to plant death.
Myrtle rust symptoms on plants can look like:
Rusts are a kind of fungal disease that affect plants. They get the name rust because they produce large numbers of tiny rust-coloured spores. Myrtle rust is a fungal disease caused by the fungus Austropuccinia psidii that only affects plants in the myrtle family.
New Zealand has a variety of native plants that belong to this family including pōhutukawa, mānuka, kānuka, rātā, swamp maire and ramarama. Other plants in the Myrtaceae family include the introduced fruit species feijoa and guava and commercially grown species such as eucalyptus.
When a plant becomes infected with myrtle rust, the disease affects the young, soft, actively growing leaves, shoot tips and young stems. At the very early stages symptoms are invisible to the naked eye. Even in the later stages of infection myrtle rust can be very difficult to detect, as some symptoms can look similar to insect or other types of damage.
In New Zealand our understanding around susceptibility continues to increase. Some examples where risk is high include:
An extensive list of susceptibility is available Download Myrtle Rust Susceptible Host Species [PDF, 477KB]
The photos below show how myrtle rust can affect plants over time. Photo credit: BioHeritage National Science Challenge.