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

Puccinia psidii (Myrtle rust)

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

Myrtle rust (Austropuccinia psidii) 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.

If you think you see the symptoms of myrtle rust on your plants: Don't touch it.
Please do not take a specimen into your garden centre to have it identified, 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 on the affected area of the plant. Email photos and relevant details to info@mpi.govt.nz 
Remember, don't touch it or try to collect samples as this may increase the spread of the disease.
Myrtle rust easily attaches itself to clothing, raising fears that people returning from an infected area will spread the spores throughout New Zealand. There is no way to eradicate it.

The latest news https://www.mpi.govt.nz/protection-and-response/responding/alerts/myrtle-rust/

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 fungus infects the foliage and causes dieback of actively growing tips on several myrtaceous plants.
On 3rd of May 2017, Myrtle rust was discovered in a tree nursery in Kerikeri, Northland among five pohutukawa seedlings.
On 17th May 2017 in New Plymouth, Taranaki
On the 21st of May 2017 at Te Kuiti in the Waikato.
On 12 June 2017 at Te Puke, Bay of Plenty
On 8 September 2017 on 2 properties in the Otorohanga township
On 23 November 2017, a serious infection of several hundred Lophomyrtus (ramarama) plants has been confirmed on a commercial plant production property in the Waimauku area of West Auckland.
In early January 2018, an exotic tree Agonis flexuosa was found infected in New Plymouth’s Pukekura Park.
As on 13 January 2018 so far, 210 sites across the country are confirmed to contain affected trees. Almost half - 101 cases - are in Taranaki, while four are in Northland, 32 in Auckland, 47 in Bay of Plenty, 22 in Waikato, and four in Wellington.
On 27 February 2018 The Ministry for Primary Industries (MPI) said that as of 27 February, myrtle rust had affected 313 properties across six regions: Northland (four properties), Auckland (43), Bay of Plenty (80), Waikato (29), Taranaki (149), and Wellington (8).
On 6 April 2018 The Ministry for Primary Industries (MPI) and the Department of Conservation have confirmed the destructive plant disease has been found on ramarama in the Tasman region at the top of the South Island, which means it is now established in almost all regions identified as vulnerable. Myrtle rust has been detected on 547 properties across nine regions: Northland (4 properties), Auckland (82), Waikato (61), Bay of Plenty (123), Taupo (5), Taranaki (233), Manawatu (3), Wellington (34), Tasman (2).
The government agencies are now giving up on trying to eradicate this disease.

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.

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 waxflower buds.

Myrtle rust on Syzygium jambos (Malabar Plum)

Thanks to Wikipedia for text and information: