More than 1,800 flies released to minimise spread of invasive weed

More than 1,800 stem-galling flies have been released by Townsville City Council to minimise the spread of the highly invasive Siam Weed (Chromolaena odorata).

The Siam Weed is a restricted invasive species that smothers native plants and can cause skin irritations and asthma in allergy prone people and poison livestock due to the high levels of nitrate found in the plant.

Community Health, Safety and Environmental Sustainability Committee chairperson Maurie Soars said Siam Weed negatively impacts the community with Council engaging with stakeholders to attempt to minimise the spread of the weed.

“Council has been working with the Department of Agriculture and Fisheries’ Tropical Weeds Research Centre to release over 1,800 of the Siam Weed stem-galling flies into areas throughout Townsville,” Cr Soars said.

“The flies work by laying eggs in the plant’s stem, stunting the plant growth and significantly reducing the number of flowers and seeds produced.

“The stem-galling flies are particularly useful for the management of the weed in difficult terrain that makes access almost impossible.”

Biosecurity Queensland Senior Science Technician Kelli Pukallus said Townsville City Council’s proactive approach with the project has been invaluable.

“More than 8,000 flies have been released into the local government area with the assistance of landholders and stakeholders,” Ms Pukallus said.

“We have seen plant gall numbers at release sites increase over the years and the fly spread to new Siam Weed areas which is positive for long-term control of the weed.”

Cr Soars said an integrated pest management approach to the Siam Weed is important for minimising impacts and any further spread of the weed.

“The Siam Weed was designated as ineradicable in 2012, and since then focus has been on impact reduction and spread minimisation,” he said.

“This bio-control method was approved for use in late 2018 and was rolled out in Townsville in early 2020 – it isn’t a one-stop fix for the control of the weed, but it is another tool in our arsenal.”

Landholders can obtain stem-galling flies for their properties by calling Townsville City Council on 13 48 10 or the Department of Agriculture and Fisheries on 13 25 23.

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