Phytophthora Cinnamomi

dead grass tree The image shown here is of a grass tree which has suffered root dieback brought on by Phytophthora cinnamomi. Soon the grass tree will fall to the ground and break apart. Other plants nearby are likely to be affected.

Phytophthora cinnamomi (Pc for short) is a fungal-like organism which attacks the roots of plants and trees causing die-back. There are species of phythophthora endemic to Australia but present thinking is that Pc is an introduced exotic pathogen. It reduces the ability of an affected plant to take up water, hence placing it under stress. The organism is thought to have been introduced by the early settlers at the beginning of the 19th century. In extreme situations it is possible for adult trees such as eucalypts and angophora to die within days. Pc is spread through the soil by water and can affect native plants, horticultural species, and exotic ornamental plants. It is very difficult to diagnose requiring microscope examination at high magnification. Plants all over Australia have been affected, from the West coast to the Eastern seaboard.

In NSW surveys have been carried out in the past five years, mainly in National Parks. For example, Pc has been found in the Royal, in Sydney Harbour, Barrington Tops, and others. The closest Parks to St Georges Basin where Pc has been identified are Booderee (including the Jervis Bay Botanic Gardens), and Murramarang. Research is being carried out by the Royal Botanic Gardens Sydney (RBGS), the National Parks and Wildlife Service, and the NSW Dept of Agriculture. Plants are affected to differing degrees. Xanthorrhoea (grass trees), for example, are very susceptible to Pc, while casuarinas are not. Pc can apparently pass through an area which appears to recover, the more susceptible plants having died off. The net effect is a decrease in floral diversity, which leads in turn to a general decrease in biodiversity.

A fungacide (Phosphite) is useful in controlling Pc. It does not kill or eradicate the organism but does help the defence mechanism of plants. Treatment is usually by spraying but individual adult trees have been treated by injection. In West Australia aerial spraying has been carried out. Control measures include the cleaning of footware, camping gear, spades, etc when leaving an infected area. Vehicles also will need cleaning on exiting an effected area. Concentrated detergent, bleach, and some proprietary products have been used for cleaning.

On the 1st of June 2003 a major conference on Pc was held in Sydney. The above information comes mainly from an associated auxiliary seminar given by Dr Brett Summerell of the RBGS

Further Information

Royal Botanic Gardens Sydney ( www.rbgsyd.nsw.gov.au)


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