THE plant killing pathogens devastating forests in the South West are increasingly becoming a problem in Perth where they are spread by human activity.
Murdoch University forest pathologist Paul Barber says numerous varieties of the water mould Phytophthora have infected the Perth urban forests and are widely associated with the premature deaths of trees and shrubs across the metro area.
Dr Barber says the main source of infection is the supply of diseased soil and plant stock.
It is further spread through green waste and mulch from diseased trees, which is often reused or sold, and through soil lodged in machinery.
“The majority of contractors pruning and removing diseased trees will not be aware if they are infected with Phytophthora,” he says.
“There is also a belief among some that Phytophthora is only transferred via soil, however, lesions from Phytophthora can be present many metres above the ground in the main trunk.”
The cost of removing and disposing trees killed by Phytophthora and planting new ones can cost tens of thousands of dollars per tree.
Dr Barber says the spread of the pathogen is intensified by the continual destruction of vegetation for agricultural and commercial development.
“This loss of vegetation causes greater stress on the remaining vegetation, is facilitating the spread of pathogens such as Phytophthora, and has a negative impact on not only our biodiversity, but also our society’s well-being,” he says.
The most deadly strain, Phytophthora cinnamomi, is less common in Perth due to the sandy soil but Dr Barber says many other species, often overlooked, are present and should be given just as much attention.
“Our knowledge of many of these species is very limited as the research simply has not been carried out,” he says.
“Some of these poorly known or undescribed species could be potentially more damaging than Phytophthora cinnamomi.”
Dr Barber says he is encouraged that many local councils are taking a proactive approach to Phytophthora management by developing a risk assessment of vegetated sites, monitoring changes in vegetation condition to detect outbreaks, and implementing management strategies.
“A much greater value should be placed on the vegetation within the Perth urban area, with policies implemented to ensure those who manage our vegetation are required to do so sustainably. This is currently not the case,” he says.
“The future well-being of our biodiversity, and the quality of life that we currently experience within Perth, depends on the future sustainable management of our urban forest.”