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Recent Publications

Alert Weed Fact Sheets

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Biological control of weeds fact sheets

List of weeds banned from sale in SA (PDF 312.5 KB )

Biological control of weeds

What is Weed Biocontrol?

Biological control (biocontrol) is generally considered to be a highly cost-effective weed management method. In Australia, investment in weed biocontrol has provided exceptional benefits; it has been shown that for every $1 invested in biocontrol there has been a return of $23 to the economy.

Weed biocontrol can play an important part in an integrated control program - the use of natural enemies (particular insects, mites or diseases) can significantly reduce the costs of chemical and other non-chemical weed control methods. These natural enemies are called biocontrol agents.

Biocontrol does not aim for, nor is it likely to achieve complete eradication of the target weed. Successful biocontrol will, at best, reduce the vigour and abundance of the weed, which reduces economic losses caused by the weed. Biocontrol is therefore not suitable for all situations, especially when rapid control or eradication is required.

A plant's natural enemies help keep it in check in their country of origin. However, when a plant enters Australia without its natural enemies, numbers of the plant can increase to such a degree that it becomes a serious pest, and is then regarded as a weed.

Biocontrol of weeds, involving the release of natural enemies, limits the growth and spread of a weed and reduces its impact on the environment. These biocontrol agents can impact on various parts of the plant (e.g. roots, crown, leaves, stems, flowers or seeds) and the plant’s life cycle (e.g. early growth, flowering or seedling phases).

 

Gorse spider mites and their webbing

Gorse spider mite:  Image: Eric Coombs, Oregon Department of Agriculture, bugwood.org

Gorse spider mite used as a biologoical control on gorse.

Gorse spider mite webbing on gorse.  Image: Eric Coombs, Oregon Department of Agriculture, bugwood.org

 

What are the key steps in a biocontrol program?

The development of a successful weed biocontrol program is a long and complex process involving the following key steps:

  1. Selection of biocontrol agents

    - Searches for natural enemies of the target weed are conducted in its country of origin. Of the known natural enemies, the most likely candidates for biological control of the weed are selected for further screening.

  2. Host testing

    - Exhaustive studies are carried out to ensure that the candidate biocontrol agent will attack only the targeted weed and not other vegetation. Tests are conducted first on plants closely related to the target weed.

  3. Release and establishment

    - Once a biocontrol agent is approved for release from quarantine, the agent is mass-reared and released at sites containing the target weed under suitable conditions.

  4. Evaluation

    - The biocontrol agent is then evaluated to determine its impact on the target weed. This evaluation can determine the reasons a biological control agent may not have worked as well as anticipated.

    Biological Control of Weeds: The Process (CSIRO) (external PDF 2.1MB )

Weed biocontrol agents in South Australia

South Australia has a long history of weed biological control. The earliest releases were made as far back as the 1930s, however most releases have occurred in the past 20 years.

History of releases in SA

This table lists all weed biocontrol agents that are known to have been released in South Australia up to July 2011, whether or not they are currently established on the target weed. Document: Biocontrol of weeds history in SA Table. (pdf 105.9 KB )

Current biocontrol agents in SA

Over 30 biocontrol agents are actively being used to control a suite of target weeds in South Australia and are listed in the following table. There are 20 weeds against which at least one biocontrol agent has been released and become established in this State. Document: Currently established biocontrol in SA table. (pdf 128.1 KB )

Possible future releases in Australia, including SA

Australian researchers are working to identify new biocontrol agents, either to augment other agents that have already been released, or to target new weeds not yet subject to biocontrol.
Document: Table - agents in testing. (pdf 14.3 KB ) 

Weed biocontrol factsheets

Biological control of Blackberry in SA ( 213.4 KB)
Biological control of Boneseed in SA ( 121.9 KB)
Biological control of Bridal creeper in SA ( 144.4 KB)
Biological control of English broom in SA (js 130.0 KB)
Biological control of Gorse in SA ( 142.9 KB)
Biological control of Horehound in SA ( 137.7 KB)
Biological control of Salvation Jane in SA ( 135.2 KB)

Case studies of weed biocontrol in SA

Salvation Jane biocontrol - a State overview

In the past Salvation Jane, was a dominant and widespread pasture weed in South Australia. Nowadays in many parts of the state, Salvation Jane has been reduced to a minor weed of pastures, and is kept in check by four biocontrol agents that act on different parts or stages of the plant. Read the Salvation Jane biological control case study for SA (pdf 80.6 KB )

 

Salvation Jane in flower

Salvation Jane. Image by Joseph M. DiTomaso,
University of California – Davis, bugwood.org

Mogulones geographicus, common name Root Weevil

Root weevil, whose lava feeds on roots of Salvation Jane and is 1 of 4 biocontrol agents.  Image, Josef Dvoøák, www.biolib.cz

  

Bridal creeper rust - making a good biocontrol agent work even better

Bridal creeper rust fungus is one of three agents released to help reduce the impacts of bridal creeper in Australia. Since it was first released a concerted effort by various government agencies, community groups and individuals has led to one of the most successful biological control programs to date.

The rust fungus damages bridal creeper by infecting the leaves and stems of the plant. When a site becomes heavily infested with the rust fungus, it can become a useful nursery site from which rust can be collected and distributed to other sites where uninfected plants can be inoculated.

Early attempts to spread the rust fungus amongst bridal creeper infestations were done by hand, which was laborious and time consuming. A novel method developed by members of the Kangaroo Island Asparagus Weeds Committee in 2003 has proved to be a very successful means of distributing the rust fungus on a large scale. This method involves spraying a solution of spores ("spore water") onto bridal creeper using readily available spray application equipment. Learn how to make spore water (ppt 859.5 KB )

 

Leaf hopper nymph on bridal creeper

Zygina sp. (leaf hopper) nymph and pustule of Puccinia myrsiphylli (rust fungus) on bridal creeper
Image by: Flickr photos/eyeweed, Creative Commons license 3.0

 

bridal creeper leaves showing dmaage caused by the leaf hopper insect

Leaf hopper damage on bridal creeper.  Image by S. Ivory,
SARDI - biocontrol

   

bridal creeper leaves showing damage caused by rust fungus

Bridal creeper leaves infected with self-introduced rust fungus.  Image by: Murray Severinsen Bay of Plenty Regional Council

 

Weed biocontrol contacts

Local weed biocontrol inquiries can be directed to your regional Natural Resources Management Board.

Further information

the following links are to external websites

General biological control websites

Boneseed

Gorse

Salvation Jane

Cape/Montpellier broom