What to do when identifying myrtle rust in Tasmania

When myrtle rust disease was first detected in New South Wales in 2010, Australia’s federal and state governments initiated an emergency response.

The urgency could not be understated. Back in its native South America, the fungus causes what is known as guava rust (Puccinia psiddi), which can be devastating to the common guava tree.

Despite the attempts of Australian industry experts and property owners, efforts to contain the fungus ultimately failed. Since its arrival, the strain now known as Austropuccinia psidii has developed affinity for a number of eucalyptus species here in Australia.

Unlike NSW and Queensland, myrtle rust has not been recorded in Tasmania’s native ecosystems and is mostly confined to private gardens and plant nurseries. Up until recently, Tasmania’s cold winters have kept myrtle rust at bay. However, increasing average annual temperatures mean that range extending species are becoming more persistent in southern latitudes as we have seen across the globe.

Keeping myrtle rust out of our native ecosystems is a joint responsibility, and our best weapon against its spread is identification.

In this article we will answer:

How do I identify myrtle rust?
How does myrtle rust spread?
What should you do if you find it
What to do when finding myrtle rust in the natural environment
What to do when finding myrtle rust in your garden

Figure 1. The yolk-yellow spores of myrtle rust.

How do I identify myrtle rust?

Myrtle rust will affect any tree in the Myrtaceae family. You may be surprised that it doesn’t affect Tasmanian Myrtle trees, as these are in the Nothofagaceae family. The Myrtaceae family is one of the largest, which means myrtle rust is capable of infecting 382 native Australian species. Many recognisable trees are within the Eucalyptus, Agonis, Melaleuca, Metrosideros, Leptopsermum and Callistemon genus’. Knowing what trees are most vulnerable to myrtle rust is the first step in correct identification.

The first signs of a myrtle rust infection are “chlorotic”. That is, an infected tree will display a loss of the colour green, resulting from insufficient chlorophyll.

Discoloured spots will appear on leaves and shoots, followed by the production of yolk yellow-coloured spores around the 14th day of infection. These spores will begin on the underside of the leaf before slowly spreading to both sides, see Figure 1.

These discoloured spots, or lesions, often turn a reddish-purple and then brown, sometimes keeping a purple border around the edge of the leaf. Older lesions turn grey but will continue to contain spores.

In the winter months, when signs of the disease are most visible, infected leaves will appear dark with withered tips. You may also find sandy gray spores on a darked stem, along with purple-brown discolourations on its leaves which may appear dry and curling.

Severe cases of myrtle rust in young trees can kill leading shoots, and create a squat and bushy looking tree.

Figure 2. A severe infection of myrtle rust

Figure 3. Red-purple lesions of myrtle rust disease

How does myrtle rust spread?

Like most fungi, myrtle rust spreads through the dispersing of its spores. Spores can travel by wind, animals, and humans moving plant material around.

Unfortunately for us, myrtle rust is exceptionally mobile and remarkably hard to remove once the infection is established.

In the emergency response of 2010, containment methods included removing host material, establishing buffer zones, using fungicide treatments, quarantine controls and host range testing.

What to do when finding myrtle rust in the natural environment

If you spot what you think could be myrtle rust in the natural environment (i.e. not gardens), we encourage you to call Tasmania’s all-hours Exotic Plant Pest Hotline on 1800 084 881. When reporting an infection, be sure to avoid contaminating your clothing and equipment with spores.

Do not collect a sample. Taking a photo and recording the location of the infected plant is also helpful.

What to do when finding myrtle rust in your garden

Unfortunately, removing all diseased material is also the state recommendation for myrtle rust found in your garden.

If you think you have identified myrtle rust in your garden, the best course of action is to have one of our qualified arborists come take a look. Whether the appropriate course of action is pruning or complete tree removal, the correct disposal of diseased material is paramount.

How can we help?

Tasmanian Tree Care provides professional solutions to myrtle rust for any commercial or residential property. If you’re unsure about the health of your natural assets, please contact us to organise an assessment. It’s true what they say: prevention is the better than a cure.

Images courtesy of Scot Nelson and The Royal Botanical Gardens of Sydney, with former
sourced from Flickr and listed in the public domain.

Content collected by Robert Scott

Robert Scott is a loyal and cautious trainee arborist. He is also our hardworking grounds person, managing all the work and machinery. Rob is an expert rock climber and a rapidly improving tree climber, receiving tuition from our more experienced climbers when he gets the opportunity to climb.