Historical aspects of commercial weed invasions in Australia
Weeds cost Australia 3.5-4.5 billion Australian dollars annually in loss of crop production and control costs, and also cause severe impacts to the environment. The garden/ornamental industry is a major pathway of introduction. By 2004, approximately 25;160 exotic plant species had been introduced to Australia via the ornamental horticulture industry, of which 1366 species naturalized and became weeds. While this represents only 5% of the species introduced by this industry in Australia to date, 56% of all weed species in Australia were introduced through horticulture.
Examples of species introduced through this pathway include some Weeds of National Significance: Asparagus asparagoides (Asparagaceae), Cabomba caroliniana (Cabombaceae, EPPO List of Invasive Alien Plants), Chrysanthemoides monilifera (Asteraceae), Cryptostegia grandiflora (Periplocoideae), Lantana camara (Verbenaceae), and Salvinia molesta (Salviniaceae, EPPO Alert List). State governments are well aware of the problem and are now working with the association ‘Nursery and Garden Industry Australia’.
Botanical gardens have also played a role in the introduction and dispersal of weeds. Rubus fruticosus (Rosaceae) and Mimosa pigra (Fabaceae) are two Weeds of National Significance reported to originate from collections of the Melbourne and Darwin botanical gardens, respectively. An Australian Botanical Gardens Weed Network has been developed (75 member organizations) to prevent the introduction and dissemination of known weeds from botanical gardens collections, among other tasks.
Agriculture has also been a significant source of weeds: Hymenachne amplexicaulis (Poaceae) was introduced into Queensland as a fodder plant and is now declared as a Weed of National Significance, threatening the Queensland sugar industry; Andropogon gayanus (Poaceae) was introduced as a fodder species for the beef industry in Queensland and became a serious environmental weed enhancing fire risk. It is estimated that approximately 18% of the 1300 plant species introduced into Australia for agricultural production (cropping, pasture and forestry) have become weeds.
Another significant source of weed entry is by accidental introduction. The Australian Quarantine and Inspection Service (AQIS) employs 3300 staff members who check 150 million items, 11.9 million air passengers, 1.8 million cargo containers and 13 000 international vessels each year. It is estimated that 61% of plant species introduced into Australia by accidental importation (640 species) became weeds. Such data highlights the importance of border security and the need to pay particular attention to agricultural produce shipments.
Another issue of concern is the role of Internet sales in spreading weeds. The size of the e-commerce of the plant and seed industry is very difficult to quantify due to its global nature, but a quick search using the following “generic terms” resulted in 15 million pages being found for “mail order plants”, and 5 million pages being found for “mail order seeds”. E-commerce may have accounted for 0.8% of the total Australian retail plant market in June 2004. Attempts have been made in America to develop a “do not sell list” for E-commerce. This has nevertheless proven to be a failure as those who failed to comply could gain an economic advantage over those who did comply. The Agricultural Internet Monitoring System (AIMS) represents an alternative approach involving an internet surveillance tool developed and implemented in the USA. AIMS is successful in identifying, monitoring, and engaging with websites and on-line traders who are proposing declared noxious weeds for sale. The tool has been recommended for adoption in Australia and other countries.
McLaren DA (2008) Historical aspects of commercial weed invasions – perennial grass case studies. Plant Protection Quarterly 23, 9-13.