Project reference: 2005-04
Biological control of Scotch broom (Cytisus scoparius) in New Zealand
Project description:
Background: Scotch broom (Cytisus scoparius) is a highly invasive weed of waste areas, farmed and grazed pastures, tussock grassland, forestry, and braided rivers. It rapidly forms large infestations, smothering tree plantings for forestry, completely infesting braided riverbeds, reducing pasture availability, and impacting on native revegetation.
Broom is ranked the fourth worst weed in New Zealand. Some forestry companies have suggested that broom causes up to 40% silvicultural losses in tree production.
The total annual costs of broom control in New Zealand, using chemicals alone, is around $50 million.
The current suite of biological control agents already released into NZ (the broom seed beetle and the broom psyllid) has reached the limits of what it can do–which is slow, but not halt, the spread of broom. Evaluation of these biological control agents indicates that the seed beetle reduces seed production by up to 90%, and the level of damage by the broom psyllid and the self–introduced broom twigminer can kill established plants but do not impact on plant populations in existing infestations.
The level of damage capable of being inflicted by these insects would significantly reduce both broom growth and competition with exotic forest plantations, and may even kill whole plants, thereby reducing control costs to forestry companies and improving the native environment in New Zealand.
One of the agents, a gall–forming mite, is highly host specific and prefers to attack broom in shaded sites. These are areas where most insects prefer not to live, so this mite will complement the other biocontrol agents, especially for forestry growers.
The FHRC funds could be specifically allocated to the mass rearing and release of new agents into all commercial plantation forests around New Zealand. This would most likely speed up the release and establishment of these potential biocontrol agents into areas where broom is a significant problem. Alternatively, the FHRC funds would add greatly to the resources already committed by several organisations to the North Canterbury Broom Group. This may assist with the success of their application to the MAF Sustainable Farming Fund (SFF).
It is important to note that this project relies upon significant funding from the MAF SFF and approval from the Environmental Risk Management Authority NZ to import and release these agents.
The full deliverables for the North Canterbury Broom Group consortium to improve the biocontrol of Broom are:
Year 1: Import for direct release up to 2 new agents for the biological control of broom in New Zealand. 2005/06
Outputs:
Apply to ERMA NZ to import and release all three broom agents.
Contract CABI, UK and Switzerland to collect Gonioctena olivaceae and Agonopterix assimilella.
If permission is gained from ERMA, then import Gonioctena olivaceae and Agonopterix assimilella.
Clear new agents from containment and begin mass rearing.
Make releases as they become available.
Attend meetings as necessary to keep funding groups informed.
Produce written material for distribution to forestry companies and farmers.
Year 2: Import for direct release 1 new agent (Aceria genistae) for the biological control of broom in New Zealand. 2006/07
Outputs:
Contract CSIRO, Australia, to collect Aceria genistae for importation.
Clear Aceria genistae from containment and begin mass rearing.
Make releases as appropriate.
Attend meetings as necessary to keep funding groups informed.
Produce written material for distribution to forestry companies and farmers.
Continue to mass rear and release all three new agents.
Year 3: Continue to mass rear and release all three–broom agents. 2007/08
Research Provider:
Landcare Research
