Phytophthora cinnamomi is a primary cause of dieback in the coastal forests of Victoria. In some of the commercially and environmentally valuable Victorian eucalypt forest it presents a very serious challenge to forest scientists and managers. Phytophthora cinnamomi infestations in Victoria ere first observed on Cricket Bat Willows in 1935, but there is some circumstantial evidence that it may have occurred even earlier. It was first isolated from soils in dieback-affected eucalypt forest in 1969. Field and greenhouse tests showed that it could cause eucalypt dieback disease and has a wide host range among native forest trees and shrubs. Extensive surveys provided evidence that P. cinnamomi is, in all probability, a newly introduced soil-borne fungus that infect roots. It causes permanent injury to various types of forest trees, heathlands, and understorey ecosystems growing in disease-conducive soils. the fungus is transported in infested soil carried on heavy earth-moving machinery, in diseased nursery soil and infested gravel, in water flowing through diseased areas, and on animals. P. cinnamomi kills its host when major roots and the collar are girdled. However, it is a member of the water mould group of fungi and thus requires fully saturated soils in which to make initial infections of a host through the unsuberised fine root systems. The movement of the fungus through the host depends on the plant's genetic resistance to infection. This resistance can be enhanced or suppressed, depending on the state of health of the plant, the climate, soil type, and site and stand conditions in whoch the host grows. The worst-affected forests are those growing on low-fertility soils on flat sites with impeded drainage, low stocking levels of trees and seasonally heavy rainfall during summer. At present the fungus is widely scattered along the coastal forests of Victoria, in the Grampians, and in road-side reserves, some nurseries, and many home gardens. It has been found in most urban areas in Victoria. It is rarely found in the cooler mountain forests where the soils are rich in organic matter; even if accidentally introduced into these locations it is unlikely to cause injury. In East and South Gippsland, selective logging since European settlement has removed many of the durable hardwoods, which co-incidentally are also disease resistant. This has resulted in a change in species balances; Eucalyptus sieberi and E. globidea, two fast-growing, prolifically seeding, hardwoods susceptible to P. cinnamomi have replaced the disease-resistant species. This process was assisted by an increased fire frequency caused by settlement and lack of control of the regeneration process. This predisposed the forest to fungal introduction and infection. Dieback, first noticed in East Gippsland in 1938, became more noticeable during the 1950s when selective ........
