Download Biological control of weeds

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]