Myrtle rust
Myrtle rust is a disease caused by the fungus Austropuccinia psidii. It threatens plants in the Myrtaceae (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.
The fungus harms the young, soft, actively growing parts of plants – leaves, shoot tips, buds, flowers and fruit – and it can affect seed development. Severe or repeated infections can kill the plants.
Myrtle family species in New Zealand
A collage of trees from the myrtle family that grow in New Zealand. The bottom three are all exotics. A number of these trees have a variety of species. A full list of myrtle rust susceptible host species can be downloaded from MPI.
All images sourced from iNaturalist and released under CC BY-NC 4.0: pōhutukawa, miro; mānuka, kānuka and rātā (southern), John Barkla; swamp maire and ramarama, rewielliot; feijoa, Nicolas Maine; guava (Chilean), Frits Schouten; eucalyptus (blue gum – Eucalyptus globulus), Jon Sullivan.
Symptoms
Myrtle rust thrives in warm temperatures with high humidity. It first appears in bright yellow, powdery eruptions on the underside of young leaves. As the infection grows, the yellow, powdery eruptions appear on both sides of the leaves. The pustules darken with time, and the leaves may become twisted and die.
Myrtle rust origins
The disease is native to Brazil, but it is found in many parts of the world. The fungal spores are microscopic and are easily dispersed by wind, insects and birds or by human activity. Myrtle rust was first detected in Australia in 2010. Initially, the Australian Government tried to contain the disease, but it quickly spread and became established along Australia’s east coast and then other parts of the country. As a result, the New Zealand Government banned imported flowers and foliage from Australian Myrtaceae family plants. Biosecurity officials began to develop a range of measures in case the disease spread to New Zealand.
Detecting myrtle rust in New Zealand
- Chronology of events
- Science collaboration
Myrtle rust found on Raoul Island
Tangatawhenua, iNaturalist, CC BY-NC 4.0
Myrtle rust is found on Kermadec pōhutukawa trees. Raoul Island, in the Kermadec Islands, is part of New Zealand but its location is more than 1,000 km northeast of Northland. Access to the island is strictly controlled.
Image: Kermadec pōhutukawa
Myrtle rust found in New Zealand
Department of Conservation, CC BY 4.0.
Myrtle rust is found on mainland New Zealand for the first time. Tests confirm five pōhutukawa seedlings at a Kerikeri nursery have the disease. Experts use fungicide spray and restrict the movement of plants and people.
Image: MPI Biosecurity staff bury potting mix at an infected Kerikeri nursery.
MPI and DOC co-ordinate response teams
Ministry for Primary Industries and licensed by MPI for reuse under the Creative Commons Attribution 4.0 International licence.
The Ministry for Primary Industries and the Department of Conservation check 800 high-risk sites across the upper North Island. A response team in Wellington makes plans for future efforts.
Image: Biosecurity NZ staff checking for myrtle rust.
Taranaki nursery discovery
A plant nursery in Waitara tests positive for the disease. MPI suggests that nurseries are the first to find myrtle rust due to careful monitoring.
More sites confirmed in Taranaki
Ministry for Primary Industries and licensed by MPI for reuse under the Creative Commons Attribution 4.0 International licence
Additional private and commercial properties in the region are infected. MPI considers the infectious spores have been carried in by the wind from Australia.
Image: Yellow spore clusters on a ramarama tree in Taranaki.
Plant producers and industry partner protocols
The nursery industry adopts protocols to try and prevent the spread of myrtle rust. Protocols come from the government and from industry partners such as the New Zealand Plant Producers Incorporated.
Te Kūiti plant nursery tests positive
Plants from an infected nursery had been sold to a King Country nursery, spreading the disease. Restrictions are in place to prevent the on-sale of infected plants.
Private garden in Te Puke
Experts find the disease in a 25-year-old ramarama plant. There is no connection to the Northland or Taranaki sites, and no new plants have been put into the garden. This strengthens the windborne infection proposal.
DNA sequencing and bioinformatic data analysis
University of Waikato
Having mapped mānuka’s genetic code in 2015, Plant & Food Research use bioinformatics to obtain more detailed understanding of mānuka’s genetic stocks using samples collected in collaboration with Manaaki Whenua – Landcare Research, the University of Waikato and key Māori partners.
New Zealand-Australia research
The Ministry of Business, Innovation and Employment funds science institutes in New Zealand and Australia to investigate the susceptibility of key species to myrtle rust, explore germplasm storage and develop detection systems.
52 infection sites
Ministry for Primary Industries and Department of Conservation – Te Papa Atawhai
MPI confirms 52 sites are infected with myrtle rust – 39 in Taranaki, four in Northland, seven in the Bay of Plenty and two in the Waikato. MPI continues to work with the Department of Conservation, local iwi, Te Puni Kōkiri and local councils to control the movement of plants, trees, fruit and garden waste from infected areas.
Image: Myrtle rust awareness poster
Continued containment and control
The Ministry for Primary Industries continues to work with the Department of Conservation, local iwi, Te Puni Kōkiri and local councils to control the movement of plants, trees, fruit and garden waste from infected areas.
Myrtle rust risk model
Beresford, R., Turner, R., Tait, A., Paul, V., Macara, G., Yu, Z., Lima, L., & Martin, R. (2018). Predicting the climatic risk of myrtle rust during its first year in New Zealand. New Zealand Plant Protection, 71, 332–347.
Plant & Food Research creates a mathematical model to understand and predict how myrtle rust behaves under New Zealand conditions. The model makes use of NIWA weather analysis and prediction maps.
Image: Example of a weekly map generated by the New Zealand Convective Scale Model (NZCSM)
Ōtorohanga detections
Ramarama trees on two Ōtorohanga properties test positive. Once again, there are no connections to plant nurseries or infected locations. As in other cases, the plants are destroyed and experts check all myrtle plants within a 500 m radius.
Short and medium-term monitoring sites
The Department of Conservation sets up four short-term and 40 medium-term monitoring sites on Raoul Island to provide data on the speed of disease transfer and the impacts on mature plants and regeneration.
First Auckland find
Ministry for Primary Industries and licensed by MPI for reuse under the Creative Commons Attribution 4.0 International licence
Myrtle rust is found on hundreds of ramarama plants in a commercial property in West Auckland. MPI reports that ramarama and pōhutukawa appear to be the most susceptible species in New Zealand.
Image: Lower and upper surface of infected pōhutukawa leaves found in Northland.
Myrtle rust reporter app
Scion
Northland Regional Council, Scion, Envirolink, Te Tira Whakamātaki (Māori Biosecurity Network), Biological Heritage National Science Challenge and the Ministry for Primary Industries develop a bilingual app that allows users to record and monitor potential host plants.
Myrtle rust detected in Lower Hutt
A 2 m high row of ramarama plants have their foliage sealed to prevent spore drift. After removal, the plant matter is deeply buried.
Department of Conservation land affected
jacqui-nz, iNaturalist, CC BY-NC 4.0
Infected ramarama plants and large rātā trees are discovered on Department of Conservation land for the first time. The land is in northern Taranaki.
Image: Northern rātā tree.
Palmerston North infection
The disease is found in the Manawatū region for the first time. This brings the total number of identified properties to 409 across the North Island.
First South Island location
The Tasman region confirms two locations are infected. Authorities are not surprised as climate models identified the region at high risk from windborne spores from Australia. Myrtle rust has now been detected on 547 properties across nine regions.
Local and regional councils develop management plans
As the focus shifts from eradication to managing the disease, councils such as the Auckland Council continue to develop plans for how to deal with myrtle rust. Private landowners will likely be asked to self-manage any infections.
A new approach
Public domain
MPI announces it will adopt a new approach. Eradication is no longer considered feasible so the focus moves to managing the disease. The new emphasis will be on research to treat myrtle rust, boost resistance and improve collection for seed banking.
Image: Ramarama leaves, flowers and seeds. Engraving by Walter Hood Fitch for Curtis’s botanical magazine, 1854.
Seed bank collection
Auckland Botanic Gardens
Staff from the Department of Conservation and Auckland Botanic Gardens collect disease-free seeds from myrtle species on Great Barrier Island. The seeds are assessed and prepared by the New Zealand Indigenous Flora Seed Bank (NZIFSB) and banked in the Margot Forde Germplasm Centre at AgResearch in Palmerston North.
Seed banks are important because the seeds can be used should local populations of a species become extinct. They also protect genetic variation.
Image: Botanists from Auckland Botanic Gardens support the Department of Conservation with myrtle family seed collection on Great Barrier Island.
Citizen science challenge
Scion
Scion scientist Dr Steve Pawson issues a wero (challenge) to the public to help map the disease by collecting and contributing data.
Beehive movement restrictions
The Department of Conservation puts restrictions on all beehive movements on Public Conservation Land. Research indicates that bees may be a vector for myrtle rust.
New test
Bio-Protection Research Centre announces a new test that can detect myrtle rust in 30 minutes. Developed by Dr Richard Winkworth and a team of undergraduate students at Massey University, the test is able to detect the fungus prior to the rust’s appearance. This will allow management to begin before spores are produced. The test is hailed as a cheap, robust game changer.
Teliospore stage
Biosecurity New Zealand reports local myrtle rust produces a teliospore stage. This indicates the fungus is capable of sexual reproduction. It increases the risk to the country as it allows the fungi to adapt to new environments and possibly affect new hosts.
West Coast infection
The disease is confirmed in Greymouth, the first case found on the West Coast. The Department of Conservation wants the public to help with monitoring in this area as it may help to identify natural resistance in some plants.
Myrtle Rust Science Plan
The Myrtle Rust Strategic Science Advisory Group (SSAG) releases the comprehensive, longer-term Myrtle Rust Science Plan. The plan was developed in consultation with over 50 scientists, stakeholders and Māori.
First mature tree death
The first death of a native mature tree (a ramarama) due to myrtle rust infection is reported. This increases concerns that extinction for some native myrtles could become a reality.
Waitākere Ranges infection
Auckland Council announce that mrytle rust has infected one of the country's most highly susceptible native myrtles, Lophomyrtus bullata, commonly known as ramarama in the Waitākere Ranges. The species is nationally threatened, with its conservation status classified as critical.
Genome sequenced
A trans-Tasman collaboration has enabled scientists to successfully sequence the genome of Austropuccinia psidii.
New RNA-based spray
University of Queensland scientists develop an environmentally friendly RNA-based spray to slow the spread of infection.
Detecting myrtle rust in New Zealand
This timeline follows the discovery of the fungal disease myrtle rust and its spread throughout New Zealand.
Detecting myrtle rust in New Zealand
This timeline follows the discovery of the fungal disease myrtle rust and its spread throughout New Zealand.
A co-ordinated biosecurity response
The first New Zealand myrtle rust discovery was in April 2017 on Raoul Island in the Kermadec Islands. The find was concerning as it affects Kermadec pōhutukawa trees, but the island’s strictly controlled access and long distance from New Zealand meant that the rest of the country was temporarily protected.
Initial myrtle rust locations in New Zealand
Myrtle rust became established in Australia in 2010. By May 2017, the disease was found in Raoul Island, Kerikeri, Waitara and Te Kūiti. By August 2018, New Zealand had 740 identified sites.
Unfortunately, within a month, the situation had changed. On 3 May 2017, the Ministry for Primary Industries (MPI) received notification that five pōhutukawa seedlings in a Kerikeri nursery showed signs of myrtle rust . Laboratory testing confirmed the results, and MPI immediately put a restricted place notice in effect. The nursery plants were sprayed with fungicide, movement of plants and people on the site was restricted and work began to track any plants that had left the site. MPI staff checked properties surrounding the nursery for signs of the disease. It also set up field headquarters with the Department of Conservation (DOC) and consulted iwi, industry and the local council. MPI staff began checking 800 high-risk sites across the upper North Island while DOC initiated searches on conservation land.
A second infected site was found a few days later at a nearby property . MPI began producing daily media updates, and the public were encouraged to contact MPI’s exotic pest and disease hotline and photograph plants they suspected of having myrtle rust symptoms. The plan was to confine and eradicate the disease, if possible.
By mid-May 2017, several sites in the Taranaki region had confirmation of myrtle rust in commercial and private properties. Scientists suspected that the infections were being caused by wind-blown spores from Australia rather than the movement of plants within New Zealand. A further find in the Bay of Plenty a few weeks later supported the windborne infection theory. MPI continued to contain and destroy the infected plants in places where they were found.
When myrtle rust was first discovered on mainland New Zealand in May last year, we said it would be a challenging disease to contain and eradicate but we would give it a good crack.
Dr Catherine Duthie, Ministry for Primary Industries myrtle rust response spokesperson
A new approach
Less than a year after the disease was first found on mainland New Zealand, myrtle rust appeared in the South Island’s Tasman region. This indicated that the disease had reached most of the country’s high-risk regions. MPI is no longer involved in field work to manage the disease. MPI offers advice and guidance to landowners with myrtle rust on their properties but allows the landowners to manage the plants themselves. MPI is continuing to collect, analyse and report myrtle rust data.
Myrtle rust disease progression
Myrtle rust is most likely to attack new growth on plants belonging to the Myrtaceae (myrtle) family. These images showing how the disease progresses are from A guide to identifying myrtle rust and can be downloaded from the MPI website.
MPI is also funding scientific research to better understand the disease and explore treatment and management options. Projects include monitoring natural ecosystems, research regarding tolerance and resistance of myrtle species and seed banking for the future.
What we know
By March 2019, 988 sites with myrtle rust had been identified. It appears that the most susceptible native myrtle species are ramarama, pōhutukawa and rātā. Mature ramarama tree deaths in the East Cape region were reported in 2020.
Fortunately, only low levels of infection have been detected in mānuka, kānuka and orchard plants like feijoa. New Zealand Plant Producers Incorporated provides protocols and advice for nurseries and other plant retailers.
Myrtle rust surveillance map
This map combines data from several organisations that are monitoring New Zealand for myrtle rust. It was current as of 23 February 2021. You can download a PDF version here.
Prior maps can be downloaded for, September 2019, August 2019, May 2019, April 2019, March 2019, February 2019, January 2019, December 2018, November 2018 and October 2018. Note: from May 2019 maps will no longer be produced monthly, this will be updated as and when new maps are created.
For a more up-to-date map, see the interactive version here.
Data compiled from: Ministry for Primary Industries; Department of Conservation; Plant and Food Research; iNaturalist; Myrtle Rust Reporter App; and botanical gardens.
MPI still encourages the public to be vigilant regarding myrtle rust . If you think you’ve seen myrtle rust , don’t touch it – take a photo and call 0800 80 99 66.
See the useful links section for more information about myrtle rust , how to identify it and sector advice.
Related content
The Hub's series of national myrtle rust surveillance maps ranges from October 2018 to February 2021. Use the maps to view the disease's spread and to compare data from month to month. The maps are an ideal way to practise the science capability 'Interpret representations'.
The Myrtle Rust Reporter is a citizen science project using iNaturalist to log sightings of the disease.
Australian scientists are investigating a biotechnology tool called RNA interference as a potential means of combating myrtle .
Seed banking is one tool being used to protect the Myrtaceae family.
The myrtle detection team uses PCR to identify myrtle spores. Find out about the PCR process in the article What is PCR?, which includes an animation that explains the three key steps involved in the PCR process.
Psa is another disease that has threatened New Zealand’s horticulture sector. Discover how scientists and industry worked to manage this disease in the article Kiwifruit – learning to live with Psa.
The Science Learning Hub team has curated a collection of resources with biosecurity as the context for learning. It includes suggestions on how to use images in this article to practise the science capabilities. We've also created a collection about forest health. Login to make either collection part of your private collection – just click on the copy . You can then add additional content, notes and make other changes. Registering an account for the Science Learning Hubs is easy and free – sign up with your email address or Google account. Look for the Sign in button at the top of each page.
Useful links
Myrtle rust in New Zealand hosts resources for identifying and managing myrtle including flyers, posters and other materials that can be printed or shared through social media.
Visit the Ministry fo Biosecurity New Zealand website for information about myrtle . It includes symptoms to look out for, advice to specific groups and more.
In this YouTube video from the BioHeritage Challenge, Ngā Koiora Tuku Iko, listen to Roanne Sutherland from Scion talking about monitoring myrtle .
See the range of resources under the Myrtle ora topic on the New Zealand’s Biological Heritage – Ngā Koiora Tuku Iho website.
MPI has developed online training courses about myrtle . The courses are available to everyone but are particularly suited to those running community education events. Register for the course here. A selection of the training videos are found here.
See what the Department of Conservation is doing about myrtle .
The Department of has put restrictions on beehive movements on public land.
The New Zealand Plant Producers Incorporated website has extensive industry advice concerning myrtle .
Read about the New Zealand Indigenous Flora Seed Bank project to collect seeds of both threatened and common species – including the Myrtaceae family. This DOC blog gives insight into how the Myrtaceae seeds are collected – it is an enormous task.
Hear from Ngāti Porou about what monitoring they've been doing, and what taonga could be at stake and hear about the community-focused approach they are calling for from government in this TVNZ 1News article with video included.
At the end of April 2021 it was announced that a successful trans-Tasman collaboration has enabled scientists to successfully sequence the genome of Austropuccinia psidii. Read the Landcare media release.
