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What is Dieback?
Phytophthora cinnamomi – known commonly as ‘Dieback’ or “Phytophthora Dieback”
Phytophthora cinnamomi, often known simply as Dieback is a plant pathogen which is spread in soil and causes root rot in infected plants preventing them from absorbing water and nutrients which eventually causes the death of the plant. It can be easily spread in contaminated soil or plant material being moved from one area to another.
Dieback acts like a Biological Bulldozer in bushland by killing many susceptible plant species. Over 40% (or 2,300) of the native plant species and half of the endangered plant species in the south-west of Western Australia are susceptible.
When Dieback spreads to bushland, it kills many susceptible plants, resulting in a permanent degradation of the native vegetation. It can also change the composition of the bushland by increasing the number of grasses and reducing the number of wildflower species. Native animals that rely on susceptible plants for survival are reduced in numbers or are eliminated from sites infested by Dieback.
Where is it found?
Although the disease occurs in other parts of Australia, WA suffers most from the effects of Phytophthora dieback because our soil type, susceptible native plant communities and high rainfall in the state’s south-west corner offers perfect conditions for the disease to thrive.
The disease is now also widespread around the Perth metropolitan area, in particular around the Banksia woodlands in the southern and northern suburbs of Perth, and the Jarrah forest in the eastern metropolitan area. It is becoming increasingly common in home gardens. Very few bushland sites in these areas are totally free from the disease with 30% of the bushland infested with the disease.
While Dieback has infected national parks, nature reserves and metropolitan bushland, around twenty per cent of WA’s jarrah forest and a huge sixty per cent of the Stirling Range National Park are now under attack, infecting a combined area of more than 214,000 times the size of Subiaco Oval.
How is Dieback spread?
Dieback can be easily spread by soil being moved from one area to another, which is why campers, four wheel drive enthusiasts, bush walkers and cyclists have a responsibility to prevent the spread of soil or mud around bushland. Furthermore, road construction, earth moving, off road vehicles and stock movement can all contribute significantly to the spread of Phytophthora dieback.
Soil that is warm and moist provides the best conditions for sporulation of Phytophthora dieback. In the south west of Western Australia the peak times of spread are usually spring and autumn. This is when ideal daily temperatures combine with rainfall to allow the pathogen to produce millions of spores within soil.
Dieback can also be readily spread in contaminated nursery stock and through the use of raw mulch. Private landholders should buy their plants from accredited nurseries to ensure that the plants are free of diseases such as Dieback.
How big is the threat?
Research is continuing to tackle the spread of this disease which is now recognised by scientists as a bigger threat to Western Australia’s ecosystem than salinity.
Phytophthora Dieback is estimated to cost the Australian economy in excess of $160 million annually in dealing with the national collateral costs of the disease. Current, yet conservative estimates released from an ongoing case study into the financial effects of Dieback predict that $6.4 billion worth of value in natural environments of WA’s south-west are at risk from the fast spreading disease.
Improved knowledge of its biological impact and an awareness of the long-term effects make tackling the Phytophthora problem an urgent one, with some species of native flora and fauna now critically endangered.
The interdependence of native plant and animal species is critical to the survival of our bushland and is integral to the commercial viability of Western Australia’s South West region.
Who is the Dieback Working Group?
The DWG was formed in 1996 by local government authorities, community groups and state government land management agencies concerned with the management of Phytophthora dieback. Since its formation, the DWG has sought to increase awareness and understanding about dieback across the southwest of Western Australia and encourage the adoption of dieback management procedures to minimise the spread and impact of the pathogen.
