The disease known as dieback has caused serious damage to large areas of forest, woodlands and heathlands in south-western Australia. It is caused by several species in the fungal genus Phytophthora which infect, rot and often kill the entire root systems and lower stems of susceptible plants. Approximately 40% of the plant species in Western Australia's south-west Botanical Province are susceptible to Phytophthora. In many places, populations of most banksias and some heaths may be severely affected or destroyed. A total of 720,000 ha of land in the south-west of WA was intensively mapped for dieback. Of this, 170,000 ha were found to be affected (DEC, 2006b).
Of the fifteen species of Phytophthora recorded in Western Australia, five (Phytophthora cinnamomi, P. citricola, P. cryptogea, P. drechsleri and P. megasperma) have become widely established in the native vegetation of south west Western Australia. Of these, P. cinnamomi is by far the most damaging, with P. megasperma the only other causing significant damage to the natural environment. A new species, P. multivora, has more recently been found to be well established in tuart forest south of Mandurah, and has the potential to be a significant pathogen, affecting communities not previously thought to be very susceptible to dieback disease (Scott et. al., 2008). Various other species are important to nurseries, horticulture, vegetables and pastures. These fungi spread by the movement of spores in water, and are easily spread in winter and in wetter areas. The fungi can also be spread widely by transporting soil from infested to uninfested areas. Vehicles, especially when driven off tracks or roads, can carry infested soil on tyres or underbody, and thus also have the potential to spread the disease.
Species adversely affected by dieback include representatives of many of the families of native plants. Families and genera which contain a high proportion of Western Australian flora variously susceptible to Phytophthora are:
Many of the genera listed above include taxa which are amongst the most important to the flora industry, including Adenanthos, Banksia (which now includes Dryandra), Hakea, Persoonia, Podocarpus, Xylomelum, Leucopogon, Lysinema, Verticordia and Xanthorrhoea.
The impact of infection may vary between sites due to different interactions between the site environment and the fungi. It can take up to three years after infection for visible symptoms of Phytophthora caused dieback to appear in vegetation. On other sites, up to ten years may pass before plants die.
3.1.1 Disease Management
There is no known practical method of eradicating Phytophthora in native vegetation. Disinfectants and fumigants used in horticulture are toxic to plants, are not practical or cost effective for natural ecosystems, and if used in bushland could cause damage to the native vegetation. A number of systemic fungicides are available, the most promising of which is neutralised phosphorous acid (H3PO4), also known as phosphite. Initial research indicates that applications can achieve control of Phytophthora development in infected plants. Currently, however, it is impractical to apply on a broad scale, although it has use for attacking fronts in areas of high conservation value such as populations of Declared Rare Flora. Research into the use of this chemical is continuing.
The current aims of disease management are to prevent introduction of the disease to uninfected areas, and to restrict the spread and intensification of the disease in infected areas. This is done by:
rating disease hazard (the recognition of sites of different vulnerability so that priorities can be assigned for protection);
assessing the risk of introduction (this is affected by factors such as the proximity of diseased areas, the season of access and the type of operation planned);
hygiene (e.g. cleaning of machinery, vehicles, footwear, and whether dry or moist soil conditions);
quarantine (denying access to areas);
manipulation of conditions to disfavour the disease and enhance host resistance (e.g. by appropriate road and path construction, manipulation of drainage, stimulation of antagonistic microflora, use of fungicides); and
education and training.
Management of Phytophthora dieback on lands vested in the Conservation Commission of WA (conservation reserves, State forest and vested timber reserves) is through hygiene measures which aim to prevent the introduction and intensification of the disease. The management of access in forested lands is principally achieved through the declaration of areas as Disease Risk Areas under Part VII (Sections 79-86) of the Conservation and Land Management Act 1084. Part VII may also apply to any other Crown land with the permission of the vesting authority. Other Acts, such as the Mining Act 1978-1987 and the Water Authority Act 1984, also provide for the control of access.
DEC’s policy statement on dieback management, Policy Statement No. 3 – Management of Phytophthora and disease caused by it (Appendix 4), guides management of Phytophthora dieback, including in the area of flora harvesting.
In 2003 DEC produced management and operational guidelines on Phytophthora cinnamomi which collated all previous information into a single document. This in conjunction with other procedural manuals and checklists (e.g. Dieback Hygiene Manual, Fire Control Checklists, Dieback Hygiene Evaluation) guide officers of DEC to plan and implement operations.
3.1.2 Control of Access
Control of access is a key element in minimising the vectored spread of Phytophthora dieback. The following strategies are applied to the commercial flora industry:
as a condition of the Commercial Purposes Licence, pickers may not take vehicles into areas containing, or suspected of containing, Phytophthora dieback;
pickers must use existing tracks and roads as designated by the managing agency, and are not permitted to make, cut or extend new tracks by any means;
in general, on DEC-managed lands, commercial flora harvesters are restricted to all-weather access tracks and roads (i.e. those which are open to the general public) and may not use roads, or pick within areas, which are closed due to disease risk or within disease risk areas, except as described under "Hygiene Evaluation" (see below); and
the following factors are evaluated before any commercial flora harvesting proceeds which has the potential to introduce, spread or intensify the impact of Phytophthora dieback on lands managed by DEC:
(i) Activity - whether the proposed activity needs to take place.
(ii) Hazard - site, host and climatic factors that influence the probabilities of host mortality.
(iv) Consequence - the consequences of infection on landuse and ecological values.
(v) Hygiene - the hygiene measures required to minimise the consequences.
(vi) Evaluation - the judgement of the manager regarding the adequacy of hygiene tactics to minimise the consequences to a level that is acceptable.
This procedure is referred to as the "Hygiene Evaluation". It is used as a disease management tool to determine appropriate operational hygiene after balancing the risk of disease introduction and spread against the consequences of hygiene failure.
As outlined in section 1.2 above, DEC has an inter-agency agreement with the Department of Land Administration for the management of UCL and unmanaged Crown reserves where the need for specific management has been identified. Phytophthora dieback is an issue which may require additional management of access (i.e. restriction on areas where picking is permitted). DEC evaluates management of non-DEC-managed lands for commercial flora harvesting on a case-by-case basis, and applies management to these areas as required.
3.1.3 Phytosanitary Measures
The following phytosanitary measures aim to minimise the further spread of Phytophthora dieback by flora pickers:
· all vehicles capable of carrying dieback disease from infected to uninfected areas should be washed down and pickers should therefore wash down vehicles before moving from a flora picking area (pickers are urged never to assume that any vehicle is clean, or that the site does not contain dieback if it is within the region from which dieback is known to exist);
· washdown should be undertaken on bridges, rocky crossings or hard, well-drained surfaces within dieback areas (it is important not to wash down in dieback-free areas as these might then become infected from material being washed off the vehicle);
· the washdown liquid should be a hospital grade biocide suitable for use against Phytophthora and the washdown solution should not be kept longer than 24 hours so it is best that the solution is made up fresh each day when required; and
· to make the washdown effective, excess soil must first be removed. This can be done by using a brush or spade to knock off larger clods of soil.
The responsibility for implementation of policy and prescriptions which incorporate the protection of plant communities from disease caused by Phytophthora spp. lies with DEC Regional and District staff, with assistance and advice from specialist staff. DEC’s Management Audit Branch have a role within DEC of periodically checking compliance of management activities with legislation, policies and procedures in relation to Phytophthora dieback.
In October 1996, a review of Phytophthora dieback in Western Australia was prepared for the Western Australian Minister for the Environment. The review provided a series of recommendations pertaining to dieback research, management and administration. Following the publication of the review, a Dieback Coordinator was appointed within DEC to provide for a more integrated approach to dieback management in Western Australia.
Phytophthora dieback does impact on some species listed on the Export Flora List. When monitoring or research indicates that a species on the List is being affected steps will be taken to ensure the species’ survival.