Myrtle Rust in the Tangihua forest

(Austropuccinia psidii ) is also known as guava rust and eucalyptus rust. Introduced to NZ by wind

Myrtle rusts will attack some of our best known trees the Myrtle family

The effect myrtle rust will have on out native trees is unknown. It may be limited to minor damage it may kill 1,000s of our unique trees. At present out best line of defence against myrtle rust is tracking and understanding the impact it will have on our forests.

Schools and individuals can help here as we will set up a monitoring module so at risk species can be regularly checked and students can learn what to look for. We will call these sentinel trees. Once we have identified them we will put a post beside them and set up an education program.

Myrtle Rust, is a fungus from…..

Myrtle Rust is a wind borne fungus that attacks the plants of the myrtle family. Myrtle rust originated in South America, has been transported to Asia and blown south to Australia where was discovered in April 2010 and quickly spread. It was found on Raoul island in April 2017 and New Zealand May 2017

Myrtle rust attacks young, soft, actively growing leaves, shoot tips and young stems. Initial symptoms are powdery, bright yellow or orange-yellow pustules on leaves, tips and stems. The developing lesions may cause a deformation of the leaves and shoots, and twig dieback if the infection is severe. It can also affect flowers and fruit. Infection may result in plant death.

Myrtle’s of the Tangihua bush

Of the species in the myrtle family that grow in New Zealand about 10 are found in the Tangihua ranges. There are also a number of common introduced (exotic species).

These include

What Myrtle Rust will do

Myrtle rust generally attacks soft new leaf growth, distorting or killing the new growth. Myrtle rust also makes plants more susceptible to secondary infections,

but because Myrtle rust is new no one really know the damage it will do. In Australia, the fungus has had different levels of impact on myrtle species, with some more seriously affected than others.

Queensland and New South Wales reported losing some small swamp species but many of the bigger trees, while affected, were not being killed.

In Hawaii, however, their equivalent of the New Zealand Rata was suffering badly with many hectares completely dead.

Myrtle Rust spores in Pohutakawa

Life Cycle

Spores are spread by wind to other host plants. Spores germinate and the myrtle rust fungus grows, piercing plant cells to obtain nutrients from the plant.

Myrtle rust spores require darkness, moisture and temperatures of 15–25°C to germinate. The first symptoms become visible within 3−5 days of initial infection. The new pustules can mature to release spores in 10–12 days. Spores can remain viable for up to three months.

Containing Myrtle rust

Myrtle rust is a fungus with microscopic spores and is spread across large distances by wind. This is how Myrtle rust arrived in NZ. It will continue to be spread through out NZ by and there is no way of stopping this from happening.

Even if eradication is achieved, there is an ongoing risk of reinfection from Australia.

Preventing myrtle rust damaging trees.

There is no known method of controlling the disease in the wild, apart from application of fungicide in very small areas as a last resort. This will not work.

Other New Zealand trees have had similar issue for example Cabbage tree sudden decline syndrome. Many believed this would eradicate the cabbage tree but it did not. All plant populations have a number of whom are resistance to any particular disease or fungus. Those plants then become the gene pool for the next generation.

MPI Director-General Martyn Dunne said if myrtle rust became established in New Zealand it might not be a case of saving the current trees but trying to save the next generation by breeding strains resistant to the disease.

Impact is highly variable between species, and some appear to be more resistant than others.

Myrtle Rust monitoring

We will identify in the Tangihua ranges trees that are most susceptible to Myrtle rust. We will then closely monitor them. This could be carried out as part of school camp activities. We will then be able to track its spread

Identifying Myrtle Rust

The fungus attacks the new growth of leaves and shoots, and in some species also the buds and fruit of these plants.

• leaves that are buckled or twisted and dying off.
• Individual myrtle rust spores cannot be seen with the naked eye; however large amounts of spores grouped together are visible as bright yellow/orange powdery patches on leave
• 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 see

Seed banking for Myrtle rust

To ensure we do not lose some of species of Myrtles we must breed strains resistant to the disease. To do this we must be able to identify trees which can resist the disease and collect seeds and cuttings from them

• Some seeds have already been collected but there are many others to do.
• Time is of the essence because the disease is already here and many of the relevant species have ripe seed right now.
• Collection of seeds will continue at other times of year (when certain species have ripe seed) and over multiple years to ensure we have good seed diversity and fresh viable seed.

Anyone believing they have seen myrtle rust

Anyone believing they have seen myrtle rust on plants in New Zealand should call MPI on 0800 80 99 66.

It is very important to follow the following rules

• Don’t touch!
• Don’t collect samples as this might spread the disease.
• If you can, take a photo of the rust and the plant it’s on.
• Phone MPI’s exotic pest and disease hotline 0800 80 99 66.
• If you accidentally come in contact with the affected plant or the rust, bag your clothing and wash clothes, bags and shoes/boots when you get home.

Call MPI’s Exotic Pest and Disease Hotline on 0800 80 99 66.

References.

• Northland Regional Council
• Department of Conservation
• Ministry of Primary Industries
• Wlikipeadia