Weeds of the future? Threats to Australia’s grazing industries by garden plants

Summary

This report has been produced by the CRC for Australian Weed Management. It extends an earlier publication (Grice 2003) which reported on naturalised plant species that present existing and emerging weed threats to Australia’s grazing industries. The research is underpinned by the Western Australian Department of Agriculture and Food’s “Plant Database” (Randall 2006). The database collates information from c. 1.5 million species-related records drawn from over 3000 publications and presently treats approximately 576,000 plant taxa. Used in conjunction with regional climate zones and by extrapolating from overseas weed experiences, the database provides a unique opportunity to identify weeds currently present in Australian gardens that may threaten Australia’s agricultural industries or natural environment in the future.

The research focuses on plants that are currently available in Australian nurseries because most of Australia’s naturalised flora has been introduced for ornamental purposes (Groves, Boden & Lonsdale 2005: 18, Spencer 2005: 8; Anonymous 2005: 3; Virtue, Bennet & Randall 2004). These plants also present the most immediate threat compared to species outside Australia and being in commercial trade enjoy a level of dispersal well beyond that of natural means.

The report identifies 281 introduced garden plants (Appendix 1) – as well as 800 lesser priority species (Appendix 2) – which present a significant risk to Australia’s grazing industries should they escape from Australian gardens and naturalise. The research evaluates these risks as a precursor to formal weed risk assessment. Of the 281 species:

• Nearly all have been recorded overseas as agricultural or environmental weeds (or both);

• More than one tenth (11%) have been recorded as noxious1 weeds overseas;

• At least one third (33%) are toxic and may harm or even kill livestock;

• Almost all have been commercially available in Australia in the last 20 years;

• Over two thirds (70%) were still available from Australian nurseries in 2004;

• Over two thirds (72%) are not currently recognised as weeds under either State or Commonwealth legislation.

Whilst studies of predicted economic impact have not been conducted, previous research (Centre for International Cost analysis 2001: 24, 26) has predicted that infestations of just two of the 281 species – Nassella tenuissima (Trin.) Barkworth and Onopordum nervosum Boiss. – could cost Australia up to A$82m over the next 40-60 years.