Myrtle rust is a fungal disease which affects the Myrtaceae family of plants, including river gum (Tristaniopsis exiliflora) and Johnstone River yellowwood (Ristantia pachysperma) in the Wet Tropics World Heritage Area.
First detected in New South Wales in 2010, it quickly spread to the Wet Tropics where it can affect a large number of plant species and the animals which depend on them.
Queensland Herbarium’s Dr Jarrah Wills, who is supported by the National Environmental Science Program through the Threatened Species Recovery Hub, and Department of Environment & Science’s Keith Smith provide an update on its spread and potential mitigation strategies.
Myrtle rust is a fungal disease which infects plants in the Myrtaceae family. It was first detected in Australia in New South Wales in 2010, and has spread from Gosford, NSW all the way up the eastern sea board to Bamaga at the tip of Cape York. It has also been detected in gardens in Tasmania and Melbourne. More recently, myrtle rust has spread to New Zealand, where their management response has been huge.
In Queensland, myrtle rust is generally confined to the Great Dividing Range and eastward to the coast and some islands, from the NSW border to Cape York. It is not believed to have moved into the drier eucalypt woodlands to the west, although areas of dry vine scrub have not been surveyed yet.
As the Wet Tropics harbours a huge diversity of badly impacted myrtle groups, this region is particularly susceptible to the current strain of myrtle rust. The disease seems to severely impact range restricted endemics (e.g. Gossia lewisensis), keystone ecological species (e.g. river gum Tristaniopsis exiliflora) and some large emergent trees (e.g. Johnstone River yellowwood Ristantia pachysperma).
Some species are much more susceptible than others, and there appears to be some differences in resistance between individuals of the same species and at different life stages and seasons. Some species may well be lost from at least some parts of the landscape as a direct or indirect consequence of myrtle rust.
Myrtle rust is so widespread that it is unlikely that nursery stock will cause further spread: the live plant trade, people, water and particularly wind have done a fantastic job anyway.
One concern is the potential waste of effort that may have occurred by planting vulnerable species in biodiversity plantings. That is, the seedlings may have been carefully nurtured and leave the nursery free of myrtle rust, but rapidly pick up the rust when planted in the landscape and subsequently die. However, no systematic monitoring has occurred to determine the short-term and long-term effects of the disease on vulnerable Myrtaceae in restoration plantings.
This raises an interesting conundrum: should nurseries avoid species vulnerable to myrtle rust altogether, or should they persist and use surviving plants that show strong resistance?
Should nurseries persist with control measures or stop?
Do nurseries and restoration workers have the capacity to investigate survival of planted-out species and share knowledge of which species battle through and survive? Or are nurseries better placed to avoid vulnerable species altogether in search of maximum survival rates?
Prevention of other myrtle rust strains from entering the country, selective breeding for resistance, translocations outside of the current myrtle rust range and monitoring ecological impacts as they unravel are actions that urgently need to be investigated.
If you have observations, knowledge or capacity to provide input into the myrtle rust studies, please contact Dr Jarrah Wills at email: Jarrah.Wills@des.qld.gov.au