Phytophthora cinnamomi is a soil-borne organism, often known as a root-rot fungus. It can cause dieback amongst some or all species of vegetation in the rainforest and sclerophyll forests. First discovered in the 1970s near Koombooloomba, over 200 patches have since been found - mostly in wet notophyll vine forests above 700m on acid volcanic soils (14 percent of the World Heritage Area). The long term recovery of affected areas remains unknown. The Environmental Protection and Biodiversity Conservation Act 1999 lists forest dieback caused by the pathogen Phytophthora cinnamomi as a ‘key threatening process’ throughout Australia.
Phytophthora can be present without killing vegetation. No one is sure what triggers it to cause dieback. The disease is spread by the movement of soil and water. It is suspected that soil disturbance or movement associated with the construction of a road or walking track may be a cause of virulent outbreaks. However, vehicles, bushwalkers and pigs may still transport infected soil from one place to another and cause new outbreaks. Mixing of different types of the pathogen may also be a trigger for virulence. There have been several other species of phytophthora detected in the Wet Tropics and little is known about their role. Deadly outbreaks of phytophthora may also be caused by other stresses on vegetation such as drought or previous logging activities.
Remember that dieback patches are not always due to phytophthora. They can also be caused by factors such as drought, lightning strikes and insect infestation. Dieback of rose gums has been found in various locations along the western edges of the Area including Julatten, Ravenshoe and Wallaman Falls areas, but it is unlikely that it is caused by phytophthora. The exact cause remains unknown.