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Plant Pests (Weeds) and Diseases Index of Biodiversity issues


    Threatening Processes

        At a glance

        The issue

        A plant pest or weed can be any plant that is having a negative impact on an environment or valuable resource and requires some form of action to reduce that impact. See also the Introduced Species Issue Report for more information about plant species that are naturalised in Tasmania but are not considered weeds. There are also several significant diseases, mostly a result of fungal pathogens, that are known to adversely affect Tasmanian native vegetation.

        In the case of weeds most are introduced species that are able to out-compete native plants, desirable pasture plants or crops due to either an absence of natural disease and pest controls or an aggressive capacity to dominate ground, such as following soil disturbance. Weeds are not restricted to the land-there are also many species that occur in water.

        Weeds that affect the natural environment are termed 'environmental weeds' and represent one of the most serious threats to Tasmania's biodiversity. Environmental weeds are plants that either escape or are deliberately introduced into the natural environment. They threaten the survival of native plants, animals and communities on land and in water.

        The key diseases known to cause native vegetation dieback, rot and decay in Tasmania include the introduced soil-borne cinnamon fungus or root rot (Phytophthora cinnamomi) and the naturally occurring myrtle wilt (Chalara australis).

        This 'At a glance' section provides an overview of the issue of plant pests and diseases in Tasmania. More detailed information is available in the Plant Pests (Weeds) and Diseases Issue Report. Seven indicators relating to naturalised plant species, environmental weeds, plant diseases, threatened native species and communities affected by weeds and diseases, and management strategies have been included in this Issue Report.

        A recommendation on Weeds, Pests and Diseases is provided, as well as a general recommendation on Native Vegetation.

        Favourable news

        • The introduction of the Tasmanian Weed Management Act 1999 provides for the control and eradication of declared weeds and promotes a strategic and sustainable approach to weed management in Tasmania. In 2001, 86 weed species/species aggregates were listed in the Act, of which 50 are actually found in Tasmania. Plants may be declared under the Act that are not here, or whose populations have not changed, but whose threat is recognised (the actual threat has not changed, merely its recognition). Once a species has been declared, a draft weed management plan must be compiled within 12 months. In February 2002, 30 of the 64 key 'environmental weed species' in Tasmania were listed on the Act.
        • All six weeds of national significance present in Tasmania (out of 20 species total) have had draft plans developed. The DPIWE has been a lead agency in the development of the National Gorse Strategy. By 200,2 funding had been received for strategic control of bridal creeper, willows and biological control programs for gorse and boneseed. Alligator weed (Alternanthera philoxeroides), which is a weed of national significance, was found in Tasmania but was eradicated in 2000. Similarly, Chilean needle grass (Nassella neesiana) has been found in Tasmania but is believed to be no longer present.
        • Fifteen of Tasmania's 29 municipalities are fully covered by weed management strategies. Four municipalities are only partly covered by community weed management strategies: Break O'Day, Central Highlands, Meander Valley and West Coast.
        • Tasmania's Weed Alert Network was established in 1999 in order to increase the chances of finding newly introduced or recently established weed species.
        • WeedPlan, which is Tasmania's weed management strategy, was developed in 1996. The strategy was reviewed in 2002. The outcomes of the review will assist in defining the future direction of weed management in the State.
        • The National Weeds Strategy was launched in 1997 with the aim to reduce the detrimental impact of weeds on the sustainability of Australia's productive capacity and natural ecosystems.
        • The RETICLE weed mapping database was launched in 2001. This provides a simple accurate system to help land managers record weed occurrences throughout Tasmania, and to store and share this information with others. The database helps with planning and conducting more effective weed control works on a local, regional and Statewide scales.
        • The fungus Phytophthora cinnamomi is listed as a threatening process in the Commonwealth Environment Protection and Biodiversity Conservation Act 1999. A Threat Abatement Team has been established to support the development of plans and actions to minimise the impact of Pythophthora root rot in Tasmania. The team's priority is to establish monitoring and management programs for selected populations of susceptible threatened species.
        • The prevention of Phytophthora cinnamomi (root rot) from infecting susceptible native vegetation has been recognised as the main course of action required in Tasmania. Management areas and prescriptions have been selected and developed for the 39 threatened species that are currently identified for protection from Phytophthora root rot in Tasmania. This is being developed by Forestry Tasmania under a program funded by the Australian Government's Department of Environment and Heritage.
        • A line of research also being investigated in Australia is the application of fungicides to increase the ability of treated plants to resist Phytophthora root rot, but the action does not kill the fungus.
        • There are guidelines and prescriptions included within the Forest Practices Code 2000 (Forest Practices Board 2000) that aim to minimise the disturbance to myrtles from forestry activities. Disturbance can often lead to the increased infection and death of trees by the fungus Chalara australis (myrtle wilt).

        Unfavourable news

        • In Tasmania there are 744 naturalised vascular plant species and seven known non-vascular plants (e.g. seaweeds, mosses, lichens). Of the vascular plants, 162 are considered weeds.
        • In 2001, there were at least 64 introduced plant species considered to be key 'environmental weeds' in Tasmania.
        • In 2001, six of the 20 weeds of national significance were present in Tasmania, including: bridal creeper, boneseed, blackberry, gorse, serrated tussock and willows. In aggregate, one or more of these are found across an extensive range of vegetation communities and land uses. The last five of these are known to be impacting upon 66 already threatened native plant species and 30 threatened and/or bioregionally important vegetation communities.
        • Between 1999-2001, 13 new weed alerts were identified of which seven are known to adversely impact biodiversity values and 12 of the 13 are known to affect agricultural production.
        • Ten municipalities are currently without weed management strategies: Brighton, Burnie, Central Coast, Devonport, Hobart, Kentish, Kingborough, King Island, Latrobe and Northern Midlands.
        • Between 1996-1999 permanent monitoring plots for Phytophthora root rot recorded appreciable mortality in selected rare or threatened species from the disease. This included the death of an average 48.4% Epacris babata, 33.2% E.limbate, and 25.9% Pultenaea hibbertiodes threatened native plant species.
        • The vegetation in Tasmania most affected by Phytophthora root rot are heathland, moorland, and dry schlerophyll forest and scrub.

        Uncertain news

        • The number of naturalised species is likely to be underestimated for groups that are comparatively less well-researched. For example, knowledge is greater for vascular plants compared to non-vascular plants and species belonging to the Kingdoms Fungi (true fungi) and Chromista. The implications of this lack of knowledge mean there is little understood about the impacts of these types of weed species upon Tasmania's native species and ecosystems.
        • As there is often a considerable delay (many decades) between introduced species becoming established and then becoming pests, it is highly likely that the percentage of pest species will increase in future even without further introductions.
        • No trends and changes in the number of declared weeds under the Weed Management Act were available because of the comparatively short period in which the legislation has been in operation. Over time, tracking the number of listed weed species will provide a measure of changes in the magnitude of the declared weed problem in Tasmania.
        • The impact of Phytophthora root rot over time in Tasmanian native vegetation types is yet to be scientifically documented. To gain an accurate picture of impact requires monitoring over long time periods (20-30 years). The real distribution of Phytophthora root rot will never be known. Mapping is often restricted to localised priority areas, with the maps soon becoming out-of-date and unreliable. This is exacerbated by the fact that Phytophthora root rot is not easily detectable in the field and relies on laboratory identification.
        • Recent documented research (after 2000) on myrtle wilt in Tasmania was unavailable at the time of this SoE Report. However, further information is provided within the Special Features Issue Report.

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        Last Modified: 14 Dec 2006
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