Grains Research & Development Corporation (GRDC), Media Release, 25 September 2025
A team of world-leading researchers from CSIRO, Australia’s national science agency, are exploring if a small insect, the stem-boring weevil, Lixus caudiger, could hold the key to tackling flaxleaf fleabane; one of the most invasive and costly weeds in Australian grain production.
The research, an investment by the Grains Research and Development Corporation (GRDC), aims to deliver biological control solutions for fleabane, a weed that costs Australian growers significantly each year in lost yields and control costs.
CSIRO is working closely with international collaborators in Brazil and France to identify and test fleabane’s natural enemies, and the weevil which is native to South America has shown promising results from early trials.
This specific weevil feeds on fleabane leaves and stems, while its larvae burrow inside the stem tissue, hollowing out plant structures and weakening them until they collapse. The internal feeding often prevents the weed from flowering and setting seed, cutting into the weed’s ability to spread.
The colony of weevils, housed in CSIRO’s quarantine facilities, is undergoing further testing, with researchers carefully monitoring feeding, mating, egg-laying and larval development across a wide range of test plants. If the insect proves safe and effective, CSIRO will prepare submissions for regulatory approval before any potential field release.
The weevil is the focus of CSIRO entomologist Dr Michelle Rafter’s research and is one of several new potential weed biological controls unveiled by Dr Ben Gooden in a keynote presentation on Wednesday at the South Australian Weeds & Pests Conference in Adelaide. Dr Gooden said the weevil research was part of a broader push to expand weed control options as part of GRDC’s weed management investigations.
“The weevil is just one of four promising fleabane biocontrol candidates, but it’s shaping up as potentially one of the most impactful,” Dr Gooden said.
CSIRO Principal Research Scientist, Dr Michelle Rafter said her team researching the weevil was witnessing promising signs that Lixus caudiger is highly specialised to fleabane, while not causing any damage to the crops themselves.
“So far, our testing shows the weevil is restricted to fleabane and its close relatives. That’s exactly what we want in a biocontrol agent, something that hones in on the target weed without threatening native plants or crops,” Dr Rafter said.
Flaxleaf fleabane (Erigeron bonariensis) has become a headache for farmers across the northern, southern and western grain growing regions where it flourishes in non-cropped areas like fence lines and roadsides, sending clouds of wind-borne seed back into cropping paddocks.
GRDC Manager Weeds, Sarah Morran, stressed the importance of identifying cutting-edge weed control innovations on behalf of Australian grain growers and said investment in biocontrol was a priority because of its potential for cost-effective, long-term weed suppression.
“Weeds cost growers significant amounts of money and impact on crop yields. By investing in innovative approaches like biocontrol, we’re helping growers tackle herbicide resistance, using nature’s own checks and balances to help manage weeds more sustainably,” Ms Morran said.
Weed biocontrol is not designed to eradicate weeds but to reduce impact and allow other management practices to be more effective.
“Weeds like flaxleaf fleabane won’t be beaten by chemicals alone. Integrated solutions, including biological control, could offer a sustainable pathway to protecting yields and profitability,” Ms Morran said.
The project with CSIRO is in addition to the GRDC national Weed Management Initiative (WMI), a 5.5 year program bringing Australia’s leading researchers and communications and extension specialists together to work on innovative, cutting-edge weed management research, development and extension.
WMI aims to provide sustainable and effective weed management strategies through four nodes across Australia, ensuring both national collaboration and regional specificity.
While it may take several years before the weevil could be released into paddocks, the CSIRO research team is optimistic.
“Finding a safe, effective biocontrol agent takes patience, but the payoff is worth it,” Dr Rafter said.
About us: GRDC is one of 15 Rural Research and Development Corporations (RDCs) responsible for planning, investing in and overseeing research, development and extension (RD&E) for 25 leviable grain crops. Our purpose is to invest in RD&E to create enduring profitability for Australian grain growers.
