In this section:
Cape Broom
Biological control of Cape broom (Montpellier), Genista monspessulana
Principal Investigator: Ken Henry
Technical Officers: Nathan Luke, Susan Ivory, Dr Angela Lush, Dr Joanne Kent
Potential Cape broom biological control agent, Arytinnis hakani (PDF)
The Cape broom problem
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Cape broom (or Montpellier broom), Genista monspessulana (L.), is a woody legume weed (Figure 1) with significant current and potential impacts on forestry production, biodiversity of natural ecosystems, grazing systems, access to amenity areas and fire risk. Infestations occur in all temperate states of Australia, with particularly severe infestations in the Adelaide Hills, southern Tasmania, central and southern Great Dividing Range of NSW and central Victoria. Cape broom is ranked 37th in the weeds nominated for Weeds of Natural Significance (WoNS) (Thorp and Lynch 2000), with a particularly high impact score due to its formation of dense, impenetrable thickets arising from a long-lived soil seedbank. Genista monspessulana is distributed throughout south-eastern Australia (Figure 2). It is prevalent in Victoria, South Australia, New South Wales and south-east Queensland, mainly growing in sclerophyll forest, open woodland and along roadsides and railways. There are also infestations in Tasmania and Western Australia. |
Figure 1. Cape broom, Genista monspessulana, with flowers and pods at Candelo, NSW. |
Figure 2. Distribution of G. monspessulana in Australia
(source: Australia’s Virtual Herbarium (2008) www.chah.gov.au/avh)
Current control methods
Current control methods within the Forestry industry generally consist of herbicide applications and the cost associated with these applications is estimated at $132/ha (W Richardson, P Yardley, pers comm.). Control methods are generally more expensive in areas of native vegetation, and are dependant on the control methods used.
Mechanical removal of G. monspessulana can potentially increase soil erosion and reinvasion of the cleared area by other weeds. Spraying with herbicides and associated additives can potentially harm non-target organisms, and may pose a contamination threat to waterways and the soil environment. Chemical handling also presents an occupational health and safety risk to spray operators.
Biological control agent – Cape broom psyllid Arytinnis hakani Loginova
CSIRO and CRC Weed Management Systems (Weeds CRC1) commenced investigations into biocontrol of Cape broom in 1999-2000, with additional investment from the State of California, as part of the International Broom Initiative (http://www.cal-ipc.org/ip/research/biocontrols/broom/index.php). This work identified the Cape broom psyllid, Arytinnis hakani Loginova (Hemiptera: Psyllidae), as a potential biological control agent and studied its biology to develop testing protocols. Arytinnis hakani is native to the western Mediterranean and not found on eastern G. monspessulana populations. It is abundant on Cape broom in the western Mediterranean, has several generations per year and can cause high levels of reduction in leaf area (Sheppard 2000).
The biological control of G. monspessulana has the potential to slow growth, reproduction and spread of the weed. Biological control allows for some level of control in difficult to access areas and areas of low weed management priority. Damage by A. hakani in the broom garden at CSIRO’s European Laboratory in Montpellier France has shown heavily attacked plants, exhibiting shoot-blackening, reduced growth and reduced flowering (Sheppard 2000). Both nymphs and adults of A. hakani insert their mouthparts into G. monspessulana buds, leaves and pods, inject saliva and suck sap and cells. Large populations of this psyllid often occur on G. monspessulana, especially on young actively growing foliage (Sheppard 2000).
Cape broom psyllid lifecycle
The Cape broom psyllid is a sap sucking plant louse that can complete several generations in a year. Egg to egg generation time varies between 30 and 60 days depending on season (Figure 3).
Eggs can survive over winter until spring, when first instar nymphs emerge and begin feeding on leaves and buds. Observations suggest that as temperatures increase over summer there is a decrease in the number of late nymphal instars and adults. The psyllid appears to survive the hot dry summer months as early instar nymphs sheltering in the youngest leaves.
Figure 3. Arytinnis hakani life cycle
Adults – Adults have wings and are mobile with bright green, mid-green or yellow-green bodies. Adults are approximately 2-3 mm long, with transparent wings that have light brown veins. Females lay their eggs amongst fresh leaves and buds and have been known to lay over 200 eggs. Up to five generations can occur per year, with four generations developing in spring and possibly one in autumn.
Eggs – Eggs are less than 1mm long and are laid on young leaves and flower buds. They vary from cream to orange in colour and are an oblong/teardrop shape. Eggs are very difficult to detect with the naked eye.
Nymphs – Nymphs are wingless but can be quite mobile on their host plant. There are five nymphal stages in this psyllid. From 1st instar to 5th instar the colour changes from orange to bright green. Second instars are approximately 1 mm long and 5th instars are just over 2 mm long.
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Arytinnis hakani eggs |
Second and fifth instar nymphs |
Adult Arytinnis hakini |
Impact on Cape broom
Nymph and adult A. hakani insert their mouthparts into Cape broom plants, injecting saliva and then sucking plant cells and sap. Infested Cape broom can be identified by the presence of green/orange nymphs and crystal-like sugary deposits. They are most likely to be found on young leaves in the growing tip.
Plant damage can be impressive with heavily attacked plants suffering from shoot-blackening, reduced growth and flowering. High-density populations of A. hakani can occur on Cape broom, especially on young actively growing foliage. In the Adelaide Hills, reduced flowering and seed set has been observed as a result of A. hakani infestation, as well as decreased shoot growth.
Arytinnis hakani has the potential to slow the growth, reproduction and spread of Cape broom. It will complement existing herbicide and physical controls, as an additional control method for integrated weed management practices. It will provide a level of control in native vegetation and in areas that are difficult to access.
Approval
The application for the approval for the release of the psyllid was submitted July 2008. The discovery of A. hakani in South Australia resulted in a change of protocol for the approval of this agent as a biological control agent for Cape broom. It was decided that each state should act independently to approve the release of the A. hakani within their borders. To date Tasmania, Victoria and recently New South Wales have approved A. hakani as a biological control agent available for release against Cape broom. The Australian Weeds Council did not oppose A. hakani being classified as a biological control agent.
References
Australia’s Virtual Herbarium (2008) www.chah.gov.au/avh
Sheppard, A.W. (2000). Survey and selection of agents for the biological control of Montpellier Broom, Genista monspessulana, CSIRO Entomology, Contracted Research Report No. 59 (unpublished) p59.
Thorp, J.R. and Lynch, R. (2000) The Determination of weeds of national significance, National Weeds Strategy Executive Committee, Launceston
Collaborators
SARDI
CSIRO Entomology
Forestry SA
Adelaide & Mt Lofty Ranges Natural Resources Management Board (AMLR NRMB)
Tasmanian Institute of Agricultural Research (TIAR)
South Australian Dept of Water, Land and Biodiversity and Conservation (DWLBC)
SA Department for Environment & Heritage (SA DEH)
Tasmania Department of Primary Industries & Water (TDPIW)
Tasmania Parks & Wildlife Service (TPWS)
Funding provided by
Land & Water Australia
Forestry SA
Adelaide & Mt Lofty Ranges Natural Resources Management Board (AMLR NRMB)
South Australian Dept of Water, Land and Biodiversity and Conservation (DWLBC)
Contacts
If you would like further information on the biological control program for Cape broom contact Ken Henry or Susan Ivory.
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