Bill Dunstan

Introduced Phytophthora pathogens in the southwest of western Australia are having a devastating impact on native plant communities. More than 41% of the 5,710 described plant species are susceptible to P. cinnamomi with P. multivora, P. elongate, and P. constricta and a number of other newly described Phytophthora spp. having similar and extended host ranges. Research is emphasizing understanding the biology and pathology of these pathogens and understanding their potential impact in a changing climate. Recently, P. cinnamomi was shown to survive asymptomatically as an endophyte or biotroph in annual and herbaceous perennials, allowing it to survive indefinitely in infested areas. Due to widespread society concern about the loss of plant species and communities and subsequent impacts on ecosystem function and health, there is significant and active society engagement with regards to management, friends groups, accurate disease mapping, prioritization of areas protectable for 50–100 years, phosphite applications and in the case of industry, attempts at eradication. We will highlight new findings with regards to the biology of these Phytophthora spp. and discuss types of community engagement on-the-ground and at the policy level aimed to stop further spread and impact of these Phytophthora pathogens into pristine but susceptible plant communities.

Worldwide Phytophthora diseases have significant direct and indirect impact on flora and fauna. In south-west Western Australia approximately 41% of the 5710 described plant species across a large number of plant families are susceptible to P. cinnamomi a pathogen listed as ‘a key threatening process’ to Australia’s biodiversity by the Commonwealth Government. P. cinnamomi in Western Australia is considered a ‘Biologial Bulldozer’ because of its ability to permanently change the structure and function of plant communities and the species they support. Through anthroprogenic activities this introduced exotic pathogen and related species are now widely distributed and many unique plant community types are now infested or threatened. Concerted effort is now spent on mapping its occurrence, identifying areas that are pathogen-free, considered protectable in the medium to long-term and have high conservation value. This presentation will discuss the biology of Phytophthora as a genus and what makes them such devastating plant pathogens, the methods used to diagnose and map their occurrence and the procedures used to select ‘protectable’ communities of high value. Case studies will be used to discuss the impact of the pathogen on plant communities in terms of floristics and habitat change and how this in turn impacts on native fauna and ecosystem function. Control strategies including communication, hygiene implementation measures, the aerial application of phosphite and the use of eradication techniques for spot infestations will be also be discussed with regards to their benefits and possible detrimental effects to native plant communities.

Here we demonstrate that management scale containment and eradication can be achieved for Phytophthora dieback infestations in three different native plant communities in Western Australia. The communities include: (1) a Kwongan vegetation type on a soil varying from sandy to exposed rocky subsurface to a clay above a rock subsurface, (2) a Proteaceous heathland on a deep sand profile, and (3) a Kwongan Banksia woodland on a deep sand over a sandy loam‐clay. All of these communities are highly impacted by P. cinnamomi resulting in substantial loss of biodiversity assets. The successful approach taken involved the following tasks: risk assessment of the project goals and proposed techniques, implementation of hygiene plans, extensive and intensive soil and plant sampling and in situ baiting to accurately map the occurrence of the pathogen, detailed hydrological characterisation using remote sensing techniques, 2D hydraulic modelling, development of hydrological engineering options, catchment modelling, installation of fences to reduce animal vectoring, herbicide applications to remove living host support for the pathogen, phosphite foliar sprays, fumigation with metham sodium and ongoing monitoring of the sites to demonstrate the success of the approach taken. Prevention of further spread through these high priority natural ecosystems is now of high priority. This project has involved partnerships between government and non‐government agencies, industry, researchers and community groups. These partnerships have included the construction of hygiene infrastructure around priority National Parks and the engagement of key stakeholders in the management of Phytophthora Dieback. The approach described has huge potential for the eradication and containment of other soil‐borne Phytophthora species around the world.

We have developed protocols to contain and eradicate spot infestations of P. cinnamomi. The strategy is based on two assumptions: In the absence of living hosts, P. cinnamomi is a weak saprotroph, and at many sites transmission is probably by root‐to‐root contact and not by propagule movement through soil water. At two P. cinnamomi infested sites, within scrub‐heath in south‐western Australia and woodland in Tasmania, we applied a succession of treatments that included (1) vegetation (host) destruction, (2) fungicides, (3) fumigation, and (4) physical root barriers. Phytophthora cinnamomi was never recovered at any of three assessments up to 24 months after treatments. Given the high rates of recovery of P. cinnamomi from untreated infested soil and the sampling effort, the probability that we failed to detect the pathogen in treated soil was low to very low. This study demonstrates for the first time that P. cinnamomi can be eradicated from natural ecosystems. The methods have application in the containment of large infestations of P. cinnamomi, and we are now looking at applying the methods over large areas. These will be discussed.

Stream baiting is a useful tool to determine if Phytophthora species are present in a catchment. The method assumes that Phytophthora species accumulate in water bodies and then spread throughout catchments with water movement. However, it is poorly understood how well Phytophthora species accumulate, survive and move within water catchments. This study investigated the ecology of P. cinnamomi collected from seven water bodies within a single mine site. Each water body varied in terms of the organic particulates, dissolved chemicals, water influx and water recycling regimes. Water quality had a significant impact on the sporulation and infection of plant baits by P. cinnamomi in each water body. The findings and implications of stream baiting as a catchment‐level monitoring tool will be discussed.

The Eucalyptus rudis (flooded gum) is in decline across its range in the south-west of Western Australia. It is a keystone species in riparian ecosystems where it provides important ecosystem functions such as habitat provision and water quality maintenance. Symptoms of decline resemble dieback symptoms caused by pathogens from the genus Phytophthora. The rhizosphere soil of E. rudis, and water, were sampled along several watercourses in the south-west and species of Phytophthora isolated. Several species were recovered from soils and water, including P. multivora and P. elongata, two species which are believed to be involved in Eucalypt decline. None of the species recovered acted as primary pathogens on E. rudis in pathogenicity tests, but they may be acting in conjunction with other biotic and abiotic factors in the field. Several different treatments, including phosphite, insecticide and complete (macro- and micro-) nutrients, were tested on mature E. rudis in a Perth wetland to compare their effectiveness in restoring health. The health of these E. rudis were also assessed using aerial remote sensing imagery. The results of this study will have significant implications for the diagnosis and treatment of Eucalyptus rudis decline.