What is Dieback? 

How is it spread?

It is believed that Phytophthora dieback was introduced to Western Australia around the time of European settlement (1828) in soil around the roots of cultivated plants. The first noted impact associated with the disease was observed in the Jarrah forest in Karragullen in 1921 where increasing number of patches of healthy Jarrah forest were dying. The cause of these plant deaths was the subject of much speculation . It was only in 1964 that Frank Podger and George Zentmyer established that Phytophthora cinnamomi was the agent responsible for these plant deaths in the Jarrah forest. During the period before the pathogen was identified as the cause of Jarrah dieback it was extensively spread throughout the south-west when infected gravel was used for road construction.

Autonomous spread of the pathogen is generally slow and is achieved through movement of the pathogen by root-to-root contact. Faster autonomous spread is accomplished through the movement of microscopic spores (zoospores) in surface and sub-surface water flows, and by animals. Autonomous spread up slope and on flat ground is relatively slow (approximately 1 m per year).

However, it is human activity that causes the most significant, rapid and widespread distribution of this pathogen. Any activity that transfers soil and plant material from one site to another has the potential to spread the disease. Vectors for that have the potential to introduce Phytophthora dieback into healthy bushland includes:

• Mining and forestry
• Land development and earth works
• Road and drainage construction
• Contaminated nursery stock
• Off-road vehicles in bushland areas
• Illegal rubbish dumping in bushland
• Fire break maintenance