The Invasion of Native Forest by Phytophthora cinnamomi. II. Post-Infection Vegetation Patterns, Regeneration, Decline in Inoculum and Attempted Control

Abstract

Further investigations of die-back in sclerophyll forest have shown that the disease continued to spread, averaging 171 m per year over periods of 3 years. Soil disturbance and gravel removal did not result in disease when no P. cinnamomi was present. P. cinnamomi was isolated from areas showing disease symptoms, but not from unaffected areas. The pathogen was confined to the A horizon of the soil and did not penetrate the clay or B horizon. Susceptibility of eucalypts was experi- mentally demonstrated at germination, at the seedling stage, and at maturity. More than 40% of mature stringybarks (of three species) were killed on some severely diseased sites. The eucalypts of the area were rated in order of susceptibility or tolerance to the pathogen. A decline in the disease potential of infected soil with time was demonstrated, and was associated with decreased population density of the pathogen. Changes in both type and composition of the plant community were noted. The sclerophyll forest with its woody understorey became a grassy woodland. A number of woody shrubs disappeared and a variety of herbs, such as grasses, bulbs, and composites, colonized the space made available by the death of woody shrubs and die-back of the eucalypt canopy. The most successful control of the disease was achieved by injecting infected areas with Vapam. This killed everything, and a barrier zone 4 m wide injected with Vapam prevented the spread of infection over a period of 18 months.