T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Austropuccinia psidii (Myrtle rust)

Kingdom: Fungi
Phylum: Basidiomycota
Class: Urediniomycetes
Subclass: Incertae sedis
Order: Uredinales
Family: Sphaerophragmiaceae 
Genus: Austropuccinia
Species: A. psidii
Binomial name: Austropuccinia psidii
Basionym: Puccinia psidii
Common names: Myrtle rust, Guava rust, Eucalyptus rust, Ohia rust

Austropuccinia psidii, Myrtle rust is a type of rust fungus, a plant pathogen. This fungus is indigenous to Central and South America and the Caribbean. It can have very serious consequences to various species of plants in the myrtle family (Myrtaceae). It infects the foliage and causes dieback of actively growing tips.

In April 2017 the Department of Conservation reported that approximately 400 square metres of Kermadec pohutukawa trees on Raoul Island were found in late March 2017 to be infected with myrtle rust. The report said that if Austropuccinia psidii were to enter mainland New Zealand, it could affect iconic New Zealand plants such as pohutukawa, kanuka, manuka and rata, as well as commercially-grown species such as eucalyptus, guava and feijoa. This fungi infects the foliage and causes dieback of actively growing tips on several myrtaceous plants.

In May 2017 Myrtle rust was discovered in a tree nursery in Kerikeri, Northland among five pohutukawa seedlings.
Myrtle rust easily attaches itself to clothing, raising fears that people returning from an infected area will spread the spores through out New Zealand. There is no way to eradicate it.
Only weeks after it was detected in Kerikeri, the Ministry for Primary Industries (MPI) announced that the fungal infection had been detected in a Waitara nursery on 16/05/2017.

Further information about myrtle rust
Individual myrtle rust spores cannot be seen with the naked eye; however large amounts of spores grouped together are visible as yellow rust bodies. Rust spores can carry long distances on the wind
The identifying signs of myrtle rust are purple/black splotches or patches (lesions) with yellow dots on leaves and stems. These can appear as bright yellow powdery eruptions on leaves. Leaves and stems especially when young can become buckled or twist and die off.
Severe infections can kill infected plants.
By the time lesions are visible, spores are already dispersing. This makes eradication difficult as the disease is already spreading by the time it can be seen.

Identifying myrtle rust
Myrtle rust only affects plants in the myrtle family. It generally attacks soft, new growth, including leaf surfaces, shoots, buds, flowers, and fruit.

Below is a full species list of trees in the myrtle family that are found in New Zealand.

Symptoms to look out for on myrtle plants are:
1: Bright yellow powdery eruptions appearing on the underside of the leaf (young infection)
2: Bright yellow powdery eruptions on both sides of the leaf (mature infection)
3: Brown/grey rust pustules (older spores) on older lesions. 
4: Some leaves may become buckled or twisted and die off.

We are asked to reporting all sightings.
If you think you've seen the symptoms of myrtle rust, do not touch it. Call the MPI Exotic Pest and Disease Hotline immediately on 0800 80 99 66. If you have a camera or phone camera, take clear photos, including the whole plant, the whole affected leaf, and a close-up of the spores/affected area of the plant.  But don't touch it or try to collect samples as this may increase the spread of the disease.  Email photos and relevant details to info@mpi.govt.nz 

The orange uredinia. They are the fruiting body of the myrtle rust fungi and they bear urediospores. 

Myrtle rust on a guava.

Myrtle rust on guava leaves.

Myrtle rust on Chamelaucium uncinatum (Geraldton wax)  

Myrtle rust on Geraldton wax flower buds.

Myrtle rust on Syzygium jambos (Malabar Plum)

Thanks to Wkipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/