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Weed Biological Control Pamphlet April 2008 BIOLOGICAL CONTROL OF WEEDS What is a weed? A weed is a plant growing where it is not wanted and has the potential to have a detrimental effect on economic, social and conservation values. Weeds tend to be plant species that have been accidentally or deliberately introduced. These introductions often grow extremely well here because the climate may be more favourable, or more importantly, because the insects or other agents which keep them in check overseas were not introduced with them. What is biological control? Biological control uses one living organism to control another. The aim of a weed biological control program is to introduce natural enemies (insects, mites or diseases) that will reduce the density of the weed to a level that is manageable and will reduce its impacts. How are biological control agents selected? Biological control agents are selected very carefully. A study is carried out overseas to identify all the organisms found attacking a weed. Some of these species will be chosen for further testing. Any agent imported for biological control of a weed must be host specific, that is, it will only attack the target plant. Stringent testing is carried out on close relatives of the weed including native, ornamental and crop plants. What happens next? Importation, testing and release of a biological control agent is regulated by the Australian Government Department of Agriculture, Fisheries and Forestry (DAFF) under the Quarantine Act of 1908. Biosecurity Australia (BA) (the Policy section of DAFF) assesses the importation of the agent and consults widely with cooperators on the hostspecificity test list and release applications. Cooperators include the Australian Quarantine and Inspection Service (AQIS), (the operational section of DAFF), the Australian Government Department of Environment and Heritage (DEH), the Commonwealth Scientific and Industrial Research Organisation (CSIRO), and relevant State/Territory government departments or research organisations. DEH also regulates the importation and release of live biological control agents under the Environment Protection and Biodiversity Conservation Act 1999. Once permission has been granted, a permit is issued and the agents are imported into quarantine. They remain in quarantine until they are bred through at least one generation to ensure that the agents are free of any possible pathogens or predators. Once the agents are certified as clean they are released from quarantine. Large numbers are then reared and released as widely as possible to ensure the best chance of establishment. If an agent successfully establishes and population densities start to increase, efficacy assessments are conducted to measure the impact on the target weed. Expectations of biological control There is no guarantee that an agent will establish after it is released or that it will control the target weed. Successful establishment and agent efficacy is influenced by a number of factors including unsuitable climatic and site conditions, insufficient numbers of individuals released, high levels of predation and parasitism and the effect of periodic plant life cycle events (plant phenology). Experience has shown that several control agents may be required to have a significant impact on a weed. Biological control will not eradicate a weed, because the agents always need some surviving plants to complete their life cycle. Rather, a successful biological control program reduces the vigour and abundance of a weed often in conjunction with traditional control methods as part of an overall integrated weed management program. Biological control programs are initially expensive and slow to develop, often taking 20 years or more to achieve success, but once in place the ongoing costs are negligible. Another advantage is that biological control agents damage only the target - a result that is difficult to achieve by mechanical or chemical control. Current and future projects The Tasmanian Institute of Agriculture (TIA) has a number of biological control programs either under-way or planned for a number of weeds including ragwort, gorse, horehound, several thistle species, English broom and boneseed. Further information For further information on this project contact: John Ireson Tasmanian Institute of Agriculture, 13 St. John’s Avenue, New Town, 7008. Phone: (03) 6233 6821; Fax: (03) 62782716 Email: [email protected]