Fighting the Triffid Take-Over: Land Managers and Scientists Are Battling a Widening Guerilla War against Triffid-Like Weed Infestations. One of Australia's Greatest but Least Known Environmental Threats, Alien Plant Species Cost the Country Billions Each Year in Containment, Eradication and Biological Control Measures
Lawrence, Louise, Ecos
As an island continent, Australia's unique ecosystems and flora were protected through the ages by isolation. That changed, dramatically, when the first European settlers arrived with foreign crops and ornamental plants. Since then, over 28 000 exotic plants have been brought into the country--only a few accidentally. Many of these alien species escaped their loose domestic controls and, away from natural predators, have revelled in Australia's conditions.
Over 2500 species of introduced plants are now firmly established in the wild. Many are threatening important wilderness areas, and the sheer cost of weed control is ballooning. Every year, half a million dollars is spent just trying to keep mimosa out of Kakadu. Although there are no figures for the total cost of managing environmental weeds, farmers spend more than $4 billion a year. It's a national headache of huge and growing proportions.
In 1997, the Australian Government set up the Natural Heritage Trust (NHT) to help restore and conserve Australia's environment and natural resources. As an integral part of that objective, CSIRO Entomology, supported by the NHT, works on an Integrated Weed Management program. With an emphasis on biological controls, program scientists now cross the world searching original ecosystems for the natural enemies of Australia's weeds. Finding a control candidate is only the beginning of a long and detailed control process (see box on page 29).
The worst weeds can form dense stands over vast areas, displacing native plants and animals and frequently reducing the recreational amenity of more publicly used land. Biological controls are preferred because infestations are often inaccessible, and because of the extensive areas affected and the risk of damage to native vegetation, control by herbicides or other means--such as fire--is restricted.
The NHT-supported CSIRO research focuses on a number of marauding 'Weeds of National Significance' (1). Its implementation also involves state departments, universities, community groups and land-holders. These organisations and CSIRO are partners in the Cooperative Research Centre (CRC) for Australian Weed Management, established to encourage and support research collaboration on sustainable management strategies to control the most problematic weeds.
In southern Australia, bridal creeper (Asparagus asparagoides), bitou bush (Chrysanthemoides monilifera) and blackberry (Rubus fruticosus aggregate) are amongst the worst environmental species.
Bridal creeper, introduced from South Africa as an ornamental plant in the 1800s, was once much favoured for wedding bouquets. Fourteen years of research have seen the release of three biological control agents from South Africa; a leafhopper, Zygina sp. (1999), a rust fungus, Pucciniu myrsiphylli (2000) and a leaf beetle, Crioceris sp. (2002). The leafhopper and the fungus are causing impressive damage to bridal creeper in southeastern New South Wales and Western Australia and are part of a national redistribution program by school and community groups. These agents have now been released at 1500 sites across Australia. The CSIRO Entomology website (2) has information on the bridal creeper work.
Many Australians encounter bitou bush, another native of South Africa, when it restricts their access to the beach. Introduced accidentally in 1908, it was later deliberately planted to stabilise soil and dunes along Australia's east coast. By 2001, bitou bush was found along 900 km (80%) of the New South Wales coast and is the dominant plant species for 400 km.
Biological control started in 1987 and two agents, the bitou bush tip moth (Comostolopsis germana) and the bitou bush seed fly (Mesoclanis polana) are well established.
In 2001/2002, a leaf-rolling moth (Tortrix sp.) was released along the New South Wales coast and has established at four sites. This was not before it worried researchers by not establishing after early releases. …