Symptoms and Signs of Phytophthora cinnamomi
The first indication that the pathogen has spread into a new area is the death of susceptible plant species. Many of these susceptible species can be used as ‘indicator' species of disease. Banksia grandis is a good example of an ‘indicator' species as once it is infected it dies rapidly and it is a large and obvious plant. Less susceptible species such as jarrah may show crown decline symptoms, including leaf yellowing and death of primary leaf-bearing branches. Epicormic branches can develop, leaves on these tend to be smaller and over time epicormic branches will decline, with an overall thinning of the crown. Trees with such symptoms can take a number of years to decline and die. In some cases, apparently healthy trees (in groups or individually) can suddenly collapse and die. The removal of bark at the base of trees just above or below the soil line can reveal areas of necrosis. These necrotic areas effectively girdle the trees and cause death.