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Biological Control of Weeds | LC0163 |
Department of Primary Industries
Updated: September 2007
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What is Biological Control
Biological control involves using one living species, the agent, to control (usually suppress) an unwanted species, the target. Many weed species introduced to Australia often do not have any natural enemies here to restrict their spread. The introduction of the weed’s natural enemies can be used to suppress it to the extent that it is no longer considered a problem.
Biological control is particularly suitable for use in weed management programs. It is also useful in controlling unwanted insects and animal pests, for example the European wasp and the rabbit. | |
How It Works
In Victoria the Department of Primary Industries (DPI) is responsible for research into the biological control of pest plants. All weed biological control research is based at DPI Frankston where a world-class quarantine facility exists.
At DPI Frankston a team of researchers study the natural enemies of target weeds. This work establishes an agent’s safety for release into the Australian environment and its effectiveness as a control agent. Only natural enemies which have a sufficiently narrow host range, and therefore are safe, will receive approval for release from the Australian Quarantine and Inspection Service and Environment Australia.
Biological control cannot eradicate a pest species. Weeds occur as part of complex ecosystems which vary according to climate and land use. This makes it difficult to predict the degree of control that can be achieved in a given situation. The effect of biological control may vary from year to year and place to place. When successful, biological control reduces the weed population and slows down its invasion of new areas.
Often biological control must be used with other control methods such as cultivation and herbicide application. Biological control means that these more traditional management methods may be needed less often and less extensively. Biological control should be considered as part of an Integrated Weed Management Program aimed at efficiently using introduced biological control agents, physical and chemical control methods and changing management techniques so that the weed is disadvantaged.
In general, biological control of weeds is best suited to infestations which have a low priority for control using chemical and cultural methods because of financial, practical or environmental constraints. In addition, sites with dense, chronic infestations and a long time-frame for control may also be suitable.
It Takes Time
Biological control programs are usually lengthy because of the time it takes to select those natural enemies of the weed which will do the most damage. This is followed by complicated studies to determine if these enemies are specific to the weed and will not attack other non-target species. Finally, the best methods for mass rearing the control agent, its release and establishment into the weed population has to be determined.
It is not uncommon for programs on one pest to span over ten years while several of its natural enemies are studied and released in Australia. | |
The classic example of successful biological control is the prickly pear earlier this century. Prickly pear once occupied more than 20 million ha of pastoral and agricultural land in south west to central Queensland and was invading new country at the rate of two ha every minute. Fifty one biological control agents were introduced over a 22 year period of which seventeen were released and twelve established. The moth C. cactorum was introduced in 1925 and had controlled most of the prickly pear infestations by 1932.
While it may take many years to effectively control a weed using biological control, benefits accumulate continually due to savings in herbicide and application costs and/or increased agricultural production. Biological control is an environmentally sound method of pest control. It poses negligible danger to non-target species and allows the weed to be gradually suppressed and replaced by more desirable species.
Biological Control Types
Increasing public concern over the use of pesticides in general has resulted in more interest being placed on biological and other non-chemical methods of control.
Another type of biological control is the use of fungal spores or bacteria in the production of mycoherbicides. To create a mycoherbicide, the spores of the agent fungi (chosen because it will only attack the weed), are mixed in a commercial formulation and applied to the weed using the same techniques as herbicide application. There are few examples of these for weed control, but formulations of the bacteria Bacillus thuringiensisare commonly used as bio-insecticides for a number of insect pests. | |
In a wider context biological control also includes the use of grazing animals. For example, goats have been successfully used to control blackberry and thistles and fish have been used to eat aquatic weeds which were choking waterways.
A natural phenomenon exhibited by some plants which can be considered as biological control is allelopathy. In this process, a plant secretes a chemical or toxin which inhibits the growth of other plants. This means there is minimum competition for nutrients and water from other plants. For example, cereal rye secretes chemicals which inhibit other plants growing around it!
The Biological Control Process
Finding suitable biological control agents for a target weed species is usually a long, involved and expensive process.
| 1. | The cost of controlling a weed is compared with the benefits to be gained from its control. This will assess whether a biological control program is worth commencing. A weed is then proposed as a candidate for biological control research to the Natural Resource Management Standing Committee (NRMSC) and Primary Industry Standing Committee (PISC). This system allows for various groups to comment on the proposed target so that any possible objections can be determined. For example, Paterson’s curse is considered a weed to graziers and a useful plant to bee-keepers.
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| 2. | The taxonomy (naming), biology and ecology of the target weed is studied both in Australia and in its native country of origin. |
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| 3. | The country of origin of a weed is surveyed for potential biological control agents. The most damaging candidates are selected for further studies. The biology, distribution and level of damage caused by the most promising agents are studied.
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| 4. | When promising candidates are determined, permission is sought from the Australian Quarantine and Inspection Service (AQIS) and Environment Australia (EA) for the importation of proposed agents into an AQIS approved quarantine facility. Here each agent is tested against an extensive list of commercial, ornamental and native plants to determine the agent’s host range. Scientific experts from each state in Australia review both the test list and results of host specificity testing.
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| 5. | Once the proposed agent is proven host specific, results of tests are submitted to AQIS and EA for permission to release. If permission is granted the agent must be bred through a minimum of one generation under quarantine conditions to ensure that it is free of its own parasites and diseases. The progeny of this initial generation can then be released into the Australian environment.
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| 6. | The best methods for breeding large numbers of each agent is then determined. Widespread releases are made at the appropriate time of year to ensure establishment and survival of the agent.
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| 7. | The agent is evaluated over a number of years. Its establishment, spread and the impact it exerts on the target weed population are assessed and the program is reviewed. |
The process of finding suitable agents, testing, breeding and finally releasing them can take ten or more years. Several more years are then needed for the agents to spread throughout the area affected by the weed.
Several species of agents and several strains of the same agent may have to be introduced to ensure that the weed is controlled throughout its distribution, especially if this spans over several different climatic zones.
Conclusion
Increasing resources have been allocated to implement biological control of pests in Australia. The research process is slow and expensive because of the need to ensure the safety of the agents that are released. However, if successful, the savings gained from having to use less of the traditional control methods will continue indefinitely.
Biological control cannot eradicate pests because the control agent eventually reaches a natural balance between itself and the target weed. Hopefully, this is at a level where the target is no longer considered a pest. Usually a combination of control methods in conjunction with biological control, must be used to achieve the desired level of control.
Further Information
Refer to other Information Notes, including the Pest Plant and Biological Control series. Contact the local office of the Department Primary Industry for more detailed advice on weed management.
Acknowledgements
Prepared by Anne-Marie Tenni (Melbourne), El Bruzzese and Melinda Newnham (Frankston), DPI, August, 1997. Updated by Greg Lefoe, David McLaren and Tom Morely, DPI, September 2007. | |
Biological Control for Victorian Weeds
| Common Name | Scientific Name | Agent Common Name | Agent Scientific Name | Mode of Action | Status |
| Blackberry | Rubus fruticosus agg | leaf rust fungus | Phragmidium violaceum | Defoliates brambles | Established |
| Boneseed | Chrysanthemoides monilifera | bitou tip moth | Comostolopsis germana | Feeds on growing tips | Released |
| black boneseed leaf beetle | Chrysolina sp. | Defoliates plant | Released |
| blotched boneseed leaf beetle | Chrysolina picturata | Defoliates plant | Released |
| painted boneseed leaf beetle | Chrysolina oberprieleri | Defoliates plant | Released |
| leaf buckle mite | Aceria sp. | Induces leaf galls | Approved for release |
| rust fungus | Endophyllum osteospermi | Induces witches brooms | Testing in progress |
| Bridal creeper | Asparagus asparagoides | leafhopper | Zygina sp. | Defoliates plant | Established |
| rust fungus | Puccinia myrsiphylla | Infects leaves | Established, |
| leaf beetle | Crioceris sp. | Feeds on young shoots | Released |
| Common heliotrope | Heliotropium europaeum | flea beetle | Longitarsus albineus | Destroys roots | Released |
| rust fungus | Uromyces heliotropli | Infects leaves and stems | Released |
| Dock | Rumex spp. | clear-wing moth | Pyropteron doryliformis | Bores into roots | Established, |
| English broom | Cytisus scoparius | broom twig mining moth | Leucoptera spartifoliella | Bores into stems | Established |
| broom seed beetle | Bruchidius villosus | Destroys developing seeds | Released |
| broom psyllid | Arytainilla spartiophila | Sucks sap | Released |
| Gorse | Ulex europaeus | seed weevil | Exapion ulicis | Destroys developing seeds | Established |
| spider mite | Tetranychus lintearius | Feeds on leaves | Established |
| thrips | Sericothrips staphylinus | Feeds on leaves | Released |
| soft-shoot moth | Agonopterix ulicetella | Feeds on young shoots | Approved for release |
| Horehound | Marrubium vulgare | horehound plume moth | Pterophorus spilodactylus | Defoliates plants | Established |
| clear-wing moth | Chamaesphecia mysiniformis | Destroys roots | Established |
| Illyrian thistle | Onopordum illyricum | stem boring weevil | Lixus cardui | Destroys stems | Released |
| seed weevil | Larinus latus | Destroys developing seed | Released |
| Paterson’s curse | Echium plantagineum | leaf mining moth | Dialectica scalariella | Mines leaves | Established |
| flea beetle | Longitarsus echii | Feeds on roots | Established |
| crown weevil | Mogulones larvatus | Feeds on crown | Established substantial impact |
| root weevil | Mogulones geographicus | Feeds on roots | Established |
| seed beetle | Melagethes planiusculus | Feeds on developing seed | Established, |
| Prickly pear | Opuntia stricta | cochineal | Dactylopius opuntiae | Feeds on aerial parts | Established |
| cactoblastis | Cactoblastis cactorum | Feeds on aerial parts | Established |
| Ragwort | Senecio jacobaea | flea beetle | Longitarsus flavicornis | Destroys roots | Established |
| flea beetle | Longitarsus jacobaeae | Destroys roots | Established |
| crown boring moth | Cochylis atricapitana | Bores into crown | Established, |
| cinnabar moth | Tyria jacobaeae | Defoliates plant | Established |
| plume moth | Platyptilia isodactyla | Bores into crown | Established |
| Scotch thistle | Onopordum acanthium | stem boring weevil | Lixus cardui | Destroys stems | Released |
| seed weevil | Larinus latus | Destroys developing seed | Released |
| Skeleton weed | Chondrilla juncea | gall midge | Cystiphora schmidti | Galls on leaves and stems | Released |
| gall mite | Eriophyes chondrillae | Galls the flower buds | Released |
| rust fungus | Puccinia chondrillina | Infects leaves and stems | Established |
| Slender thistle | Carduus pycnocephalus | receptacle weevil | Rhinocyllus conicus | Destroys developing seeds | Released |
| rust fungus | Puccinia cardui-pycnocephali | Infects leaves and stems | Established |
| Slender thistle | Carduus tenuiflorus | receptacle weevil | Rhinocyllus conicus | Destroys developing seeds | Released |
| rust fungus | Puccinia cardui-pycnocephali | Infects leaves and stems | Established |
| Spear thistle | Cirsium vulgare | receptacle weevil | Rhinocyllus conicus | Destroys developing seeds | Released |
| crown weevil | Trichosirocalus horridus | Feeds on rosette and tap root | Released |
| gall fly | Urophora stylata | Reduces seed production | Established,t |
| Spiney emex | Emex australis
Emex spinosa | stem weevil | Perapion antiquum | Mines stems | Released |
| stem weevil | Lixus cribricollis | Attacks stems | Released |
| St John’s wort | Hypericum perforatum | leaf beetle | Chrysolina hyperici | Feeds on leaves and shoots | Released |
| leaf beetle | Chrysolina quadrigemina | Feeds on leaves and shoots | Established |
| aphis | Aphis chloris | Attacks shoots | Established |
| gall midge | Zeuxidiplosis giardi | Galls leaves | Established |
| mite | Aculus hyperici | Reduces plant vigour and seed production | Established |
| Tutsan | Hypericum androsaemum | rust fungus | Melampsora hypericorum | Defoliates plant | Established |
| Variegated thistle | Silybum marianum | receptacle weevil | Rhinocyllus conicus | Destroys developing seed | Released |
The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.
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