Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Introduction of novel biota into native habitats and communities (continued)
In 1999 a coordinated national approach was put in place to deal with the threat posed by weeds to both agricultural production and the environment. The National Weeds Strategy was formally inaugurated by the federal and state ministers through the Ministerial Councils of Agriculture, Environment and Forestry. It provides the first coordinated step to monitoring weeds identified as weeds of national significance.
Table 24 lists weeds of national significance. The significance is determined on the basis of:
- potential for spread, and
- socioeconomic and environmental implications.
Table 24: Weeds of national significance and their impact.
All the species were selected, in part, because they have high impact on endangered species and habitats, and on environmental processes. They have been identified because their present distribution is large and/or potential rate of spread is rapid. Strategies for their control have been, or are being, developed.
|Weed||Origin||Safety||Pastoral||Cropping||Forestry||Water||Infrastructure||Endangered spp.||Plant communities||Cultural values||Tourism||Community||Amenities|
|Athel pine||N Africa, Arabia etc|
|Bitou bush||SW South Africa|
|Blackberry||North and west Europe|
|Bridal creeper||South Africa|
|Chilean needle grass||South America|
|Gorse||Central and west Europe|
|Hymenachne||South and central America|
|Sensitive plant||Tropical Americas|
|Parkinsonia||S USA, Mexico etc|
|Pond apple||N, Central, S America, W Africa|
|Prickly acacia||Africa, W Asia|
|Rubber vine||SW Madagascar|
|Serrated tussock||Argentina, Peru, Chile|
|Willows||Europe, Asia, America|
Source: National Weeds Strategy (2000).
An objective analysis was undertaken of the data presented on all proposed weeds, using a combination of survey information, expert panel assessment and data compiled from literature and agencies (Thorp and Lynch 2000) . Weeds are listed if they require national action for their management and score highly on the criteria listed above.
In the case of some weeds, such as bitou bush or boneseed (Chrysanthamoides monilifera), the species biology, distribution, and methods of effective control are all well understood.
Current management strategies are targeting control in coastal dune and woodland ecosystems of national parks and reserves in eastern Australia (Vanjic et al. 2000). Very widely dispersed weeds such as serrated tussock (Nasella trichotoma ) must be managed through the cooperation of local landowners. Management relies heavily on local landholders and groups such as Landcare to obtain sufficient volunteers to help in spraying, clearing, and monitoring programs. The Upper Murrumbidgee Catchment Management Authority has a community program that operates in collaboration with environment agency rangers to control serrated tussock in the southern tablelands of New South Wales (Allen 2000).
State and territory governments have the primary responsibility for managing weeds, through their constitutional responsibility for natural resources. Legislation to report and control some weed species was often among the earliest pieces of environmental legislation in a state. Declared and noxious weeds must be reported and controlled, either by the landholder or by allowing government officers access for that purpose.
The national 'Weedbusters' logo provides a readily identifiable focus for community action on weed control.
The very large preponderance of weeds originating as garden ornamentals is an issue that is currently being addressed by the Nursery Industry Association of Australia, in collaboration with the Cooperative Research Centre for Weed Management Systems and others. AQIS and the CRC are assisting in identifying those species that are currently sold as seed or plants by retail outlets, and the industry is developing strategies for withdrawing some from sale and increasing customer knowledge on correct containment. However, the occurrence of such old garden favourites as gorse, lantana, salvinia and blackberry among the list of weeds of national significance shows how difficult it will be to persuade the largely urban Australian population that such plants should be removed from gardens.
One of the most effective methods of low-cost, widespread weed control is through biological control. Australia has a very long history of research on biological control agents for the management of pest species. Some of the most well-known success stories are the control of the prickly pear with the cactoblastis moth, the control of the aquatic weed salvinia by a weevil, and the control of narrow-leafed skeleton weed with a rust fungus. Traditional biological control projects have used agents associated with the target organism in its place of origin. Briese (2000) provides a review of the effectiveness of Australia's biological control (Table 25).
|Type of control project||Weed control projects||Individual agent releases|
|Number of projects||Percentage of projects||Number of agents||Percentage of agents|
|Damage to weeds in field||41||91||90||42|
|Some contribution to control||26||58||49||23|
|Substantial contribution to control||19||42||25||12|
Source: Briese (2000).
Nearly half the introduced biological agents are having a measurable effect on controlling weeds, often in situations where other forms of control are nearly impossible, such as rough grazing areas and the rangelands.
The 1996 State of the Environment Report indicated that annual losses to agriculture, horticulture, and non-farmed areas from weeds were $2.5 billion for the previous decade. These estimates computed the production foregone from weed competition, losses from weed contamination of food and fibre, and direct costs of all methods of control. No estimate was made of the labour cost involved. No new estimates of the total cost of weeds is available, and environmental costs would be hard to estimate because biodiversity valuation does not have an agreed methodology (see the Biodiversity Theme Report).
A recent study undertaken for the CRC Weed Management Systems by the Centre for International Economics (2000) has estimated that current weed management and research is likely to provide the following returns within the next 30 years:
- $124 million to cropping industries, through integrated weed management,
- $496 million to pasture-based industries to control the grass Vulpia ,
- $253 million in environmental control of Paterson's curse, and
- $45 million in environmental control of bitou bush.
Outbreaks of serious crop and pasture diseases are generally rapidly controlled if identified early enough, because measures are taken to isolate, destroy, and restrict the movement of infected material. However, many pests and diseases start as minor nuisances, but increase in seriousness over time, depending on seasonal conditions. Weeds, pests and diseases of native vegetation and fauna are often much less controlled because the issue is one that affects everyone, but is the responsibility of no-one, and funding for research and management is not readily identifiable.
The assessment of environmental weed, pest and disease impacts has been confined largely to studies on biodiversity. However, there are notable cases where changes to vegetation structure and composition have had a marked effect on the hydrology, microclimates and nutrient cycling of particular habitats and districts. The best known are epidemic diseases that eliminate large tree species, such as chestnut blight and Dutch elm disease, in North America and Europe. In Australia, Phytophthora cinnamomi has been the most serious disease of this type.
A very exciting technical development has been the use of fungi, bacteria and other microorganisms as the agents of control. Biocides from the neem tree in India have long been used, but other sources now include scorpion's venom, pheromones from insects, and 'friendly' nematodes which are sometimes mutated by Bacillus thuringiensis (Bt) for insect control.
These agents (sometimes called biopesticides) are attractive because, being of natural origin, they are perceived as more environmentally friendly than synthetic chemicals. Biopesticides for several weed species are now at the stage of registration in North America, and many are in the developmental stage, but at present most preparations cannot compete financially with the cheaper herbicides and are not in regular commercial use. The rationale in using a microbial agent is to simulate a plague-like attack on the target organism.
The most interesting recent development has been the successful trials for control of the native plague locusts in several regions of the world through aerial application of the naturally occurring fungus Metarhizium, initially isolated from a native locust. The technique, first developed in West Africa, has been adapted for controlling Australian native plague locusts and grasshoppers with great success. The live fungus spore formulation has to be produced on a large scale and is then suspended in a light oil for the broad-scale application needed to control locusts by aerial spraying. In 2000 a very large plague locust outbreak occurred across both eastern and western Australia. In Western Australia it was the largest outbreak ever recorded, while in south-eastern Australia it was the largest since 1955. Although registration with the National Registration Authority was not complete enough for the commercial sale of the product (GreenGuard TM ) at the time of the outbreak, the Australian Plague Locust Commission was able to conduct extensive aerial trial spraying with the product to assist control. This fungal formulation has been found to be as effective as the normal pesticide treatment, with the added benefit of being more environmentally benign.
As an island continent Australia is protected from some of the most devastating pests and diseases that have affected other regions, but there are many animal and plant diseases and pests that are feared, and of concern to the AQIS and plant and health scientists. Some, such as rabies and foot-and-mouth diseases are of greatest concern because of their implications for human health and viable agricultural industries.
Others could have a devastating effect on our native fauna and flora. One recently identified potential risk is that posed by the myrtaceous rust sometimes known as 'guava rust'. This is a fungal disease of the genus Puccinia (P. psidii) that has the capacity to attack many species of the myrtle family in South America, including the exotic eucalypts introduced into that continent for commercial forestry, such as Eucalyptus grandis (flooded gum) and E. globulus (Southern blue gum). The rust appears to be able to attack many eucalypt species, and would pose an enormous threat to Australia's native eucalypt-dominated forests and woodlands if it were ever to arrive.
The proximity of Australia to the Indonesian archipelago and the direct incursion of a wide range of tropical insects, microbiota and weeds has been of particular concern to quarantine, plant and animal health officers. The Northern Australian Quarantine Strategy (NAQS) was developed to provide a strategic plan for dealing with such threats. It works from the basis that it is not possible to stop all potential incursions, and priorities must be made on the basis of likelihood of spread, level of danger posed by the organism to primary industries and the environment, and effectiveness of methods to counteract the incursion. An early warning network system has been developed of sentinel animal herds, insect traps and survey transects of the protected zones (Figure 49). The NAQS system extends protection to near neighbours of Australia on off-shore islands. Some recent examples of incursions that have literally 'blown in' have included sugarcane smut into the Northern Territory, and the mosquito bearing Japanese encephalitis.
Figure 49: Torres Strait Protected Zone and Special Quarantine Zone.
Source: AQIS (2000)
A summary of the target insects, crops and associated pathogens, and animal pests and diseases that are considered to be the most likely threats to enter via Australia's northern border are available from AQIS (2000). Many of the serious weed threats are environmental weeds of wet areas, such as wetlands, waterways and lakes, that are associated with rice cultivation in South-East Asia.
P. cinnamomi is an exotic oomycete (a fungus-like relative of algae) that attacks the vascular system of over a thousand species of native and commercial plants in Australia. It was probably introduced inadvertently in the 19th century through soil adhering to horticultural plants. Its spores are easily dispersed by water into soil, and carried in wheels and shoes.
In Western Australia, Phytophthora causes 'jarrah dieback' In affected forests, jarrah (Eucalyptus marginata), initially show symptoms of dead outer branches and then progressively dieback towards the main stem. However, in south-western Western Australia Phytophthora has also been responsible for widespread death of many banksias, and a wide range of other shrub species. In the Stirling Range National Park, Phytophthora is a threat to rare and endangered flora.
Curiously, although P. cinnamomi is found in wet parts of Australia, its impact is fortunately less devastating in the northern and eastern coastal parts of the continent. There it only causes sporadic outbreaks in the tropical wet forest regions. It is possible that the very low nutritional status of the West Australian sands and laterites increases the initial susceptibility of species in that region to attack (Tommerup et al. 1999). Phytophthora is, however, responsible for severe losses in many plantation tree crops, such as avocado in Queensland and banksia cut-flower plantations and plantation eucalypts in New South Wales. Cultural practices have been developed that control the disease in these valuable tree crops, but they are costly.
The environmental impact of this disease in jarrah forests has not been formally assessed, but must certainly have had a deleterious effect on the hydrology of areas where large numbers of deep-rooted woody perennials have been killed. Jarrah trees have extraordinarily long roots tracked to over 120 metres, and banksias also regularly root to 30-50 metres. In parts of the south-western region that have become severely affected by secondary salinity, such as the Blackwood catchment, P. cinnamomi may have had as deleterious effect as deliberate land clearing.
Dieback-affected native vegetation in south-western Western Australia.
Source: Environment Australia
Is Australia keeping pace, or is it losing battle against the introduction and spread of pests? In terms of the detection at the point of entry into Australia, the heavy investment in strict quarantine surveillance has been successful in continuing to detect and prevent incursions at ports of entry with as much success as in the past, against the increasing pressure from traffic into all ports. There are calculated risks in the operation of quarantine activities, since it will never be possible to exclude totally such organisms as fungal spores, seeds and insects that are borne on the wind, organisms carried in ship ballast water, or adhere to aircraft, ships or shoes. However, barrier detection remains highly effective.
A recent new threat comes from Internet sales of seeds, delivered by post. These present a new problem which has not yet been addressed effectively.
The real problem comes in managing outbreaks and further spread of pests and diseases that occur in organisms that are already in the country and in controlling environmental weeds and pests which are not a priority for the agriculture, forestry or fisheries industries. Many of these organisms are long established, and have already proved to be costly or difficult to suppress or eradicate.
In the past five years, however, some hopeful signs have emerged with respect to weed control, including the public recognition that weeds are a persistent threat to habitat maintenance and ecosystem integrity. One of the most promising signs of progress has been the adoption of more integrated pest management systems and a coordinated national approach leading to the adoption of strategies fitted to the biology of particular weeds.
Historically the resources allocated to weed and pest management, are small relative to the problem. However, the creation of several Cooperative Research Centres specialising in pests, disease and weeds is providing a focus for research on novel methods of control, monitoring and training. Some valuable new control technologies are emerging, such as viral diseases, biopesticides, sterile males, and immuno-contraceptives.
While Australian pest, weed and disease control science is at the leading edge, we have only had a national weed strategy for three and a half years. Cultural values are changing as a result, but it is still early days. This initiative has started to shift reliance from chemical control to an integrated management approach, typified by the Weeds of National Significance strategy, matching state strategies, regional and local plans and community involvement (John Thorp pers. comm.). Because legislation is state and territory based there is a lack of consistent and uniform legislation, which has hampered an integrated approach; but the new Commonwealth Environmental Protection and Biodiversity Conservation Act 1999 provides a mechanism for regarding weeds and other pests as a threatening process.