Dieback (or Phytophthora dieback) refers to the deadly introduced plant disease caused by Phytophthora cinnamomi. There are over 50 species of Phytophthora, but it is P. cinnamomi that causes the most severe and widespread damage to native plants in Western Australia.
Dieback is common throughout the whole of Southern Australia. In the south-west of WA it is found in areas receiving more than 400 mm annual rainfall between Jurien and east of Esperance. In sloping areas Phytophthora dieback spreads quickly in surface and sub-surface water flows. It spreads slower up-slope and on flat ground (approximately 1 m per year) because it is restricted to movement by root-to-root contact. However, it is human activity that causes the most significant, rapid and widespread distribution of this pathogen. Road construction, earth moving, driving infested vehicles on bush roads and stock movement can all contribute significantly to the spread of dieback. Bush restoration projects may also inadvertently spread the pathogen.
Over 40% of native WA plant species are susceptible to Phytophthora dieback and over 50% of our rare and/or endangered flora species are susceptible. Many of these plants are only found in the Southwest Australia Ecoregion. Some of the region’s more common plants are susceptible, including jarrah, banksias, grasstrees and zamia palms.
Phosphite is a biodegradable fungicide that protects plants against dieback. Phosphite works by boosting the plant’s own natural defences and thereby allowing susceptible plants to survive within Phytophthora dieback infested bushland. It is important to note that there is no chemical that will eradicate Phytophthora dieback, including phosphite.
Phytophthora cinnamomi is listed as a ‘Key Threatening Process to Australia’s Biodiversity’ and has had considerable impact on many plant communities throughout much of Australia. However, how the distribution and impact of P. cinnamomi will change with future climate change is currently unknown.
The Dieback Working Group is a network of people, organisations and other community groups bound by a common interest “to see an end to the human-mediated spread of Phytophthora Dieback”. See the website below for further information to join the Dieback Working Group or to find out about future events on dieback in your area.