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The White List Approach to Weeds

Andrew Cox from the Invasive Species Council has written an article about how the Weed Society of Victoria could be involved in advocacy on relavent issues.

To Support a ‘White List’ Approach to Weeds?


The executive committee has decided to develop one or more policy positions for the Weed Society that it can advance on behalf of its members. The aim would be to improve the control of weeds.


We have chosen the concept of a ‘White List’ or ‘Permitted List’ as a policy position that the Weed Society may adopt.


On behalf of the executive committee, new member Andrew Cox has prepared the following background information about this topic.


We want to hear what Society members think before we proceed. Email of fill in the online survey to tell us your views about a white list approach to weeds.



The Need for Change to Managing Weeds[1]


Prevention and early intervention are the most cost-effective techniques for managing weeds.

- Natural Resource Management Ministerial Council, Australian Weeds Strategy[2]


 Weed prevention should be practiced both at the national border (pre-border) and internally (post-border) between states/territories, and also between regions. With quarantine regulations now restricting the import of new plant species to those assessed as low risk, the major weed risks arise from plant species that were imported into Australia prior to weed risk assessment, some of which have already naturalised (established in the wild outside their natural range). Risks can also arise from native plant species moved outside their natural range. Weed prevention requires that non-indigenous plants are not spread to new locations unless they are assessed as a low weed risk.


There are more than 26,000 exotic plant species in Australia, most in cultivation in gardens and paddocks. More than 10% of these exotic species have already become established in the wild. Another 23% are weedy in other parts of the world, suggesting a potential to become invasive in Australia[3]. There are also more than 11,000 native plant species in cultivation, some 5% of which have established in the wild outside their natural range[4]. About three-quarters of the exotic weedy species found in Australia started out as cultivated plants[5] (about 65% as garden/park plants and at least 8% as agricultural plants). Gardens comprise the major pool of future weeds. Many more new weeds are likely to come from this source than from accidental or illegal introductions.


Despite the large number of cultivated plants in Australia that are weeds or potential weeds, there are very few restrictions over their movement and sale. Assuming that species weedy in other countries are potentially invasive somewhere in Australia, there are about 9000 weeds or potential weeds in Australia[6], but only a few hundred (about 500 taxa and genera) are subject to any form of legislative control in any one of Australia’s states/ territories, apart from Western Australia. There are no restrictions on the sale or movement anywhere in Australia (apart from WA) of more than 90% of weeds or potential weeds and more than 80% of naturalised species. Many of the restricted plants are restricted only in some part of their potential range. A large number of invaders and potential invaders are available for trade in Australia. Of some 8700 garden species available through nursery catalogues and seed sellers in 2002, 12% were weeds somewhere in Australia.[7]


The Black List or Prohibited List


 The unrestricted movement of thousands of weeds or potential weeds within most of Australia derives from the regulatory approach to non-native plants. In what is known as the ‘prohibited list’ or ‘black list’ approach, the sale and movement of all plant species are permitted except for those that are specifically banned by a state or territory.


Black list systems mostly result in bans on species that have already established, and often long after it is too late to eradicate them. Most declaration processes are slow and onerous. They can be preventative by banning species before they are introduced, but this is done on an ad hoc, occasional basis rather than systematically.[8]


 It is not realistic to assess the many thousands of potential weeds that could be introduced to determine which should be prohibited.[9] The system is generally non-precautionary in allowing the entry of plant species likely to be weedy with no assessment of risk.


The White List or Permitted List


The white list system takes the opposite approach of banning all species unless they are on a permitted list.[10] The latter results in a much larger number of weeds being prevented entry, as Tables 4 and 5 show. The difference between the approaches is often summed up as treating species as harmless unless proven otherwise (black list) versus treating species as harmful unless proven otherwise (white list).


The implementation of a ‘permitted list’ or ‘white list’ approach would reverse this approach, banning the movement and sale of all species apart from those specifically permitted.[11]


A permitted-list approach involves developing a list of plant taxa38 that can be legally sold and transported because they have passed a weed risk assessment and are deemed low risk. Taxa not on the list are automatically prohibited, unless they pass a risk assessment and are added to the list.


The development of a list of permitted, non-invasive taxa, applied in a consistent manner across all States and Territories, could represent the most effective and timely response to the immediate threat posed by thousands of potentially invasive and unrestricted plant species.

- Steve Csurhes, Rod Randall, Christian Goninon, Alice Beilby, Stephen Johnson and John Weiss, Turn the tap off before you mop up the spill.[12]

The permitted list approach is used in Australia at the national border, in Western Australia and in New Zealand. It is used in the Northern Territory for aquatic plants, and also by state and territory governments for some categories of exotic animals. Experience with these existing systems has shown that a permitted list approach is workable, effective and cost effective, as discussed in the next section. It is consistent with the Australian Weeds Strategy, agreed to by federal and state/territory governments in. In fact, a permitted list approach is the only way to meet the prevention goals of the strategy.


The aim of a state/territory-based white-list approach would be to prevent the deliberate movement of:


  1. Existing weeds into new regions where they are likely to invade.
  2. Potential weeds into regions where they are likely to invade.[13]
  3. Invasive or potentially invasive native plants outside their natural range.


However, as applied to date, permitted lists generally also include taxa already traded in the jurisdiction, including those that are invasive or potentially invasive. Permitted lists have generally been used to draw ‘a line in the sand’ to prevent new potentially harmful introductions, but for maximum effectiveness they should also be used to reduce the number of existing permitted species to limit future naturalisations and exacerbation of existing weed problems. White-list restrictions would apply only to the sale or movement of plants, not their possession. Thus, landholders with non-permitted plants in their gardens or paddocks would not be breaking the law, except if the plants were on a prohibited list with conditions requiring landholders to remove those species or if they were breaching a duty of care.[14]


Comparing the White list and Black list approaches


[This] represents a substantial failure of State and Territory-based environmental regulation

- Allen Hawke, Independent Review of the Environment Protection & Biodiversity Conservation Act 1999.[15]


Currently, several thousand plant species persist as ornamentals or as naturalised populations in urban settings. They represent a vast reservoir of potential future problems. Movement of these species within Australia is effectively unconstrained.


White list systems can comprehensively prevent the introduction of new weeds, depending upon how effective and precautionary the weed risk assessment is.[16]


In the first six years of operation Western Australia prevented the entry of 410 plants assessed as a weed risk.


Tests of the federal weed risk assessment protocol on known weeds found that it correctly predicted 90% of weeds and 70% of non-weeds, so some weeds are still likely to gain entry and some non-weeds are likely to be rejected.[17] The system is precautionary in rejecting plant imports that are likely to become weeds with no certainty that they would.[18] It is systematic in requiring a risk assessment for all new species proposed for import.



[1] This article is based on a backgrounder prepared by the Invasive Species Council: Stopping weed invasions: a ‘white list’ approach, December 2009. The full piece can be found at:

[2] NRMMC (2006). Australian Weeds Strategy: A national strategy for weed management in Australia. Natural Resource Management Ministerial Council.

[3] Panetta FD, Mackey AP, Virtue JG and Groves RH (2001). Weed risk assessments: core issues and future directions. Weed Risk Assessment. RH Groves, FD Panetta and JG Virtue. Melbourne, CSIRO Publishing. Note: Weediness in one part of the world is highly predictive for weediness elsewhere.

[4] There is a total of 36,630 separate species in cultivation in Australia. Randall RP (2007). The introduced flora of Australia and its weed status. CRC for Australian Weed Management and Department of Agriculture and Food, Western Australia, Adelaide.

[5] Groves RH, Hosking JR, Batianoff GN, Cooke DA and Cowie ID (2003). Weed Categories for Natural and Agricultural Ecosystem Management. Canberra, Department of Agriculture, Fisheries and Forestry; and Cook G and Dias L (2006). It was no accident: deliberate plant introductions by Australian government agencies during the 20th century. Australian Journal of Botany 54: 601-25.

[6] Other species may turn out to be weeds as well, particularly those that do not have a history of introduction elsewhere that might have revealed a tendency for invasion. In addition, changing conditions in future (eg. climate change or disturbance or introduction to a new habitat) may facilitate other species to become invasive. Most have not been here for very long in ecological terms. Many foreign plants in cultivation are thought to be ‘sleepers’, which means they may become weedy in future. Groves RH (1999). Sleeper weeds. Proceedings of the 12th Australian Weeds Conference, Hobart, Tasmanian Weeds Society.

[7] Groves RH, Boden R and Lonsdale WM (2005). Jumping the Garden Fence: Invasive Garden Plants in Australia and their Environmental and Agricultural Impacts. WWF-Australia, Sydney.

[8] While it would be possible to ban the majority of potential weeds under a prohibited list approach, in reality this would not occur because it would mean conducting a risk assessment of the many thousands of plant species that could be introduced. It would be a huge waste of resources.

[9] “To deliver comparable savings, a prohibited list approach would need to involve risk assessment of a much larger pool of species, possibly the entire world plant flora if one accepts that any plant species can be smuggled into Australia.” Csurhes S, Randall R, Goninon C, Beilby A, Johnson S and Weiss J (2006). “Turn the tap off before you mop up the spill’: Exploring a permitted-list approach to regulations over the sale and interstate movement of potentially invasive plants in the States and Territories of Australia. Proceedings of the 15th Australian Weeds Conference. C Preston, JH Watts and ND Crossman, Weed Management Society of South Australia Inc, Adelaide: 95-98. Note: Authors are all State and Territory government weed scientists/officers. Their paper specifies that it was written to stimulate discussion and does not represent government policy.

[10] They also have a black list, which includes those species already assessed as too risky or previously banned.

[11] A white list is complemented by a black list that contains those species already banned, those that do not pass a weed risk assessment and those species which should be controlled by landholders or for which there are restrictions in certain areas.

[12] Csurhes et al. (2006).

[13] They may be non-invasive in their current distribution because the climate or habitat is unsuitable, or they are ‘sleepers’ and will become invasive in future.

[14] Csurhes et al. (2006) Note this limits capacity to address the risks associated with private plant collectors.

[15] Hawke A (2009). The Australian Environment Act: Report of the Independent review of the Environment Protection and Biodiversity Conservation Act 1999. Department of the Environment, Water, Heritage and the Arts, Canberra.

[16] The extent of precaution applied depends on the level of certainty associated with particular assessments (Low 2005). Many assessments are not precautionary because the certainty is high that a species will become weedy when introduced – eg. if it is a weed elsewhere and the climate is suitable. There is much greater uncertainty if a species is not known to be a weed elsewhere, and has no weedy relatives.

[17] Gordon D, Onderdonk D, Fox A and Stocker R (2008). Consistent accuracy of the Australian Weed Risk Assessment system across varied geographies. Diversity and Distributions 14(234-42). This study assessed the accuracy across different countries in which it had been tested.

[18] Low T (2005). Preventing alien invasions: The precautionary principle in practice in weed risk assessment in Australia. Biodiversity and the Precautionary Principle. B Dickson and R Cooney, Flora and Fauna International, UK: 141-55.