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Myrtle Rust

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Myrtle rust threatens many of our native plants, and is now in Kaipātiki. Keep a close eye on your garden and local reserves, and report any sightings of myrtle rust using iNaturalist.​​

What is myrtle rust?

Myrtle rust is a disease caused by a fungal pathogen (Austropuccinia psidii) that attacks plants in the myrtle (Myrtaceae) family. The pathogen arrived in Aotearoa New Zealand in 2017. Since its arrival the disease has quickly spread across the country.

 

Myrtle rust attacks a plant’s new growth, including leaves, stems, flowers and fruit, damaging the plant. For some plants, becoming infected, or repeated infections over time can lead to whole-plant death.​​

 

How do I recognise myrtle rust?

The giveaway symptom of myrtle rust is the distinctive yellow/orange powder on new growth. At the early stages of infection this powder is found on the underside of the leaves, but will begin to cover all surfaces as the infection progresses.

 

Myrtle rust is typically found in warm conditions, so keep your eyes peeled for symptoms during the warmer months.​ Examples of different plants infected with myrtle rust can be found on the Myrtle Rust in New Zealand website or in the slideshow below.

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Myrtle Rust on pōhutukawa. Image by N. Charlton.

Why should we care about myrtle rust?
The spread of myrtle rust and loss of myrtle species threatens Aotearoa's ecosystems and culture. 

​Ecology

There is a real risk of localised extinctions of highly susceptible species like ramarama and maire tawake (swamp maire). This has already been seen in Australia, which has over 1500 species of native myrtles.

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The disease also poses a significant risk to our ecosystems. Myrtles are part of our natural environment, connected to the other plants and animals they live and interact with. The loss of a myrtle species could lead to the loss of other species that rely on them. For example, myrtle flowers support pollinators, and some native myrtles like kānuka are ‘pioneer species.’ Pioneer species can grow in barren or harsh environments, creating shelter so that other plants and animals can also 'move in.' Without native myrtles, our ecosystems would function very differently.

 

Culture

Myrtles are culturally significant. Myrtles are sources of food, medicine and materials that were (and still are) used by Māori people, and other New Zealanders. Numerous species are present in pūrākau (stories) and beliefs within Te Ao Māori (the Māori worldview). For example the ancient pōhutukawa at Te Rerenga Wairua/Cape Reinga is part of the path that spirits travel to the afterlife.

In general culture, pōhutukawa and rātā are known as New Zealand’s Christmas trees - a bright symbol of the summer holiday season.

The loss of native myrtles would lead to a loss of shared generational cultural knowledge, such as that is now felt with some of our extinct animal species.

Superspreaders

Superspreaders are plants that create a high amount of myrtle rust spores if infected. This is usually because they grow quickly, are easily infected (low or no resistance), and can survive infections. Quick growth results in more leaves/plant material for myrtle rust to infect, more infection sites means that more spores will be made and released into the air. Survival after infections means that infected plants will continue to grow and become infected.

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A key superspreader is the non-native lilly-pilly, which is a common hedge plant. They are easy to spot with their distinct red-tinged leaves. Our recommendation is to use alternative plants for hedges and replace lilly-pilly hedges if possible. If it is not feasible to replace your lilly-pilly hedge, you can prune them in winter to try minimise the amount of new growth in summer.

What should I do if I find myrtle rust?

If you think you have found myrtle rust at your own property or within a reserve, the best thing you can do is report your observation using iNaturalist. iNaturalist helps researchers monitor where the disease is, when it appears and what it infects. 

 

​You are not required to remove infected plant from your property. But, if you do wish to, you must follow hygiene measures to avoid further spreading spores:

  1. Cover the infected material (such as with a bag) before pruning.

  2. Seal the infected material into a bag and dispose of in landfill.

  3. Do not prune in windy conditions

  4. Wash exposed clothing and clean exposed equipment/tools

  5. Do not place infected or potentially infected vegetation in green waste bins or community weed bins.​​

Watch for a detailed tutorial from MPI:

​​​​​​​​How can I help?

Sharing and upskilling:

Learning about myrtle rust and teaching your whānau and community about it is one of the best ways you can help. Our resources section has some great websites to learn from.

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Myrtle rust is also covered in our Plant Pathogen Training Program which is held regularly for volunteers and members of the public. Keep an eye on our monthly newsletters or social media for when the next training will be held.

 

Another key action you can take is reporting myrtle rust. You can do this through the iNaturalist app. Encourage your friends and whānau to use it too!

 

In the Garden:

Find a list of susceptible myrtle species in the ‘helpful resources’ section below and avoid planting these.

 

If you already have myrtles in your garden, you might consider carrying out a survey of your garden for myrtle species, from which you can make decisions about managing any you do have.

We strongly advise pruning your myrtles during the winter months. This is because new growth at this time is slower and therefore available sites for myrtle rust to infect are minimised. You might also decide to remove non-native myrtles and replace them with a different species: if you do this, remember to follow the hygiene measures listed above.

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Here is a list of lilly-pilly alternatives that you can grow as a hedge.

Maire Tawake Project

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The Maire Tawake Project is a collaborative project to help conserve the indigenous wetland species, swamp maire (Syzygium maire). Maire tawake is extremely susceptible to myrtle rust and multiple re-infections will eventually lead to tree death.

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Pest Free Kaipātiki, key volunteers, and conservation organisations around Auckland have been looking after their maire tawake with the intention of fruit collection and looking for myrtle rust resistance.

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This is overseen by key myrtle rust researcher Rob Beresford and supported by Auckland Council.

Maire-Tawake, circa 1885, New Zealand, by Sarah Featon. Purchased 1919. Te Papa (1992-0035-2277/65)

FAQ

Where is myrtle rust in New Zealand?

Myrtle rust can now be found throughout New Zealand. This being said, it prefers a warmer climate and may be restricted by environmental factors, so the most affected areas are in the North Island.

Why try stop myrtle rust?

Myrtle rust is a major threat to the bio-cultural fabric of our country. Myrtles are important to our ecosystems and in our cultures.

How Does Myrtle Rust spread?

Myrtle rust spreads mainly through the air, however it can also spread through the movement of infected plant material, movement by pollinators and contaminated items.

What plants can get myrtle rust?

Myrtles are in the Myrtaceae family. This includes those in the Metrosideros (pōhutukawa), Leptospermum (mānuka), and Lophomyrtus (ramarama) genera; and Syzygium maire (swamp maire).

Not all species in each genus are susceptible.

There are also a range of non-native plants that are susceptible.

It's everywhere, why try?

Though myrtle rust can be found throughout New Zealand, plants have a range of infection rates. One factor that can affect infection is sporeload. High sporeload (more spores in the air) can put more pressure on plants. This could mean that species that may have some resistance, could still get infected. This is why it is important to reduce 'super spreaders' like lilly pilly.

How can I treat myrtle rust?

Myrtle rust can be treated with most garden supply fungicides (those that target rusts), however caution is needed with the risk to health and developed fungicide resistance.

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