Measuring Impact: Croker Island at the Heart of Gall Fly Research for Siam Weed Management
'We cannot control what we do not measure.'
Croker Island is now the centre of a two-year collaborative study launched in August 2025 by the NT Government’s Weed Management Branch and the Queensland Department of Primary Industries (DPI).
Siam weed (Chromolaena odorata) is a highly invasive weed with significant potential to cause damage to native vegetation and agricultural areas. Siam weed is known to be toxic to stock and can have human health impacts. For more information on Siam weed please see: Siam weed | NT.GOV.AU
The gall fly (Cecidochares connexa) has shown to be a successful biocontrol agent for controlling Siam Weed.
Following successful gall fly releases and establishment across mainland Northern Australia, researchers are now turning to Croker Island — a location where the flies have not yet been introduced. This final phase of the broader gall fly release program aims to quantify the effectiveness of the gall fly in the Northern Territory, using methodology already in place in Queensland, to monitor its impact on Siam weed and guide future weed management activities across Australia.
Fieldwork is being carried out by the Weed Management Branch’s Michelle Franklin (Weed Scientist), Joshua Maeer (Siam Weed Project Officer), Gerald Danao (Weed Science Technical Officer), Queensland DPI’s David Comben (Weed Biological Control Technical Officer), and Chainsaw (Garngi Ranger), whose combined expertise is driving this critical research forward.
Do not attempt to control Siam weed by yourself. If you have seen Siam weed, please contact the Weed Management Branch on 08 8999 4567 or weedinfo@nt.gov.au.
