Myrtle rust is a fungal disease caused by Puccinia psidii, and is also known as eucalyptus rust or guava rust in other parts of the world. It is native to South America but has spread to Central America, the Caribbean, Mexico, USA, Japan and China. This disease infects plants belonging to the Myrtaceae plant family – including eucalypts, paperbark, bottlebrush, tea tree and lilly-pilly. This family accounts for about 10% of Australia’s native flora (i.e. 2253 species), and 75% of Australia’s vegetation is dominated by myrtaceous plants.
Myrtle rust was first detected in Australia on 23 April 2010 in New South Wales (NSW). Subsequently the disease spread along the east coast of New South Wales and it was first detected in Queensland on 27 December 2010. The disease is easily spread by the movement of infected plant material as well as by spores dispersed by wind, water, animals, clothing, footwear, garden tools and vehicles.
The most obvious symptom of the disease is a covering of bright yellow spores on juvenile leaves, and the rust can also attack younger stems, and developing fruit. Myrtle rust reduces the growth and vigour of infected plants, with new growth and young plants being worst affected. The disease impact varies depending on the susceptibility of the species and local growing conditions (i.e. aspect, microclimate, etc.). However, it may eventually lead to plant death in some situations.
Myrtle rust has the potential to impact on the nursery trade, forestry, bush regeneration activities, private and public gardens, amenity areas (e.g. parks, gardens, playgrounds, etc.), the cut flower industry, honey production and the plant oil industries. It may also have significant environmental impacts such as reducing biodiversity, threatening endangered species, damaging ecosystems (i.e. reducing their resilience to weed invasion and other diseases), limiting flowering and seed production, and impacting on fauna (e.g. koalas, gliders, birds, and insects). Myrtle rust could also reduce the recreational value of natural areas, and will undoubtedly lead to increased costs for the management or removal of infected plants and trees.
Chemical control of myrtle rust with fungicides is suitable in intensively managed situations, such as in plant nurseries, ornamental flower production and some cropping situations. However, the cost associated with the need for frequent application may be prohibitive. There will also be some use of chemical control in home gardens and amenity areas, but the most susceptible species will probably require removal rather than continual chemical control. On the other hand, the use of fungicides in natural areas may be limited to the protection of endangered species.
The Queensland Government has implemented a “Myrtle Rust Program” with the goal of ‘helping Queenslanders adapt to living with the impacts of myrtle rust’, and limiting its effects on the economy, communities and the environment. For more information about myrtle rust or to report a suspected sighting, please visit www.biosecurity.qld.gov.au, call 13 25 23, or contact MyrtleRustProgram@daff.qld.gov.au or Suzy.Perry@daff.qld.gov.au.