Weed Control Using Exotic Biological Control Agents
What is Biological Control?
The aim of biological control is to reinstate a natural balance between an introduced weed and its new environment. This is achieved by introducing some of the biological agents which control their distribution and density in their native habitats elsewhere in the world.
Before exotic agents can be released into Australia they are extensively tested to make sure they are host specific i.e. only attack the weed species. Once these agents are approved by the Australian Quarantine Inspection Service, they are bred up usually by government agencies in laboratory and greenhouse conditions where they can be nurtured and monitored.
The next step is to establish nursery sites in areas where the target weeds are causing problems. There is no guarantee that exotic agents will be able to cope with Australian and/or Tasmanian conditions. If the agents become well established, it is then possible to use these nursery sites to supply other sites.
What can Biological Control Do?
Biological control will not totally eliminate a weed but it should reduce its vigour and abundance to a level that is either tolerable or that can be managed by more conventional means. In the long term, a more natural balance between the weed and its predators is achieved. Best results have occurred when more than one agent attacks a specific weed.
Although initial costs for testing and breeding are expensive, once established in the environment the costs to the land holder are negligible. Unlike mechanical and chemical methods, biological control agents damage only the target weed and do not take up the land managers valuable time.
Availability Of Biological Agents.
It is important to establish nursery sites in local areas under local conditions. These sites need to be protected while numbers build up. For this reason they need to be in areas where exposure to herbicides and cultivation are generally at a minimum. The specific needs will vary with the type of agents being used. Once established and acclimatised to a local area they may be transported locally to increase the rate of spread.
Biological Agents for Weed Control In the Tamar Valley.
Various states in Australia are working on different biological control agents. The Tamar Valley Weed Strategy is endeavouring to source these for release in the local area. In some cases a few trial sites will be all that is possible due to the lack of numbers available or to the lack of knowledge about how viable the agent will be in the local Tasmanian environment (i.e. mainland states will not send bulk material when the agent is not tested in Tasmanian conditions) In others there is enough material for multiple releases. Because of our ability to map the size of weed infestations using the TVWS survey sheets and record the information on the G.I.S. computer program we will be able to monitor new releases and judge the effectiveness. Once established in our area, the agents natural increase in range can be facilitated by community and Landcare groups much as dung beetles have been in the past.