Herbicide carryover is a critical consideration for farmers when they are making planting decisions. Soil testing can measure herbicide residues, but the results can be difficult to interpret and the available data on residue levels and crop impacts in Australian cropping soils has previously been limited.
Associate Professor Mick Rose from Southern Cross University led a Soil CRC project (4.2.001) that developed over 80 new herbicide-soil-crop critical damage thresholds, which can help growers and advisers interpret soil and plant tissue tests.
A/Prof Rose is also involved in GRDC-funded research which extends the Soil CRC’s findings and aims to create a tool to help growers and advisors interpret soil test results and have confidence in their planting decisions.
The GRDC project (DPI2306-013RTX) seeks to better understand and predict the persistence of herbicides in soil across a paddock and relate this to planting risk. The research involves herbicide carryover field experiments with multiple core sites established near Geraldton (2024/25) and Esperance (2025/26) in WA; Griffith (2024/25) and West Wyalong (2025/26) in NSW; Wellcamp and Toowoomba (2024-26) in Qld; and Minnipa on South Australia’s Eyre Peninsula (2024-26).
The 2024-25 results show that carryover toxicity can vary substantially within a paddock due to soil type and landscape differences, but it is difficult to predict the extent of yield loss from early season injury (biomass reduction). This has implications for soil sampling and analysis for forward-planning of rotations.
The project team are developing models to predict the spatial pattern of herbicide carryover and risk within and across paddocks, to help growers and consultants better manage these risks. You can learn more about the GRDC project by reading their latest update.
This month, A/Prof Rose shared the findings of his herbicide residues research at field walks hosted by Birchip Cropping Group and Mallee Sustainable Farming in Victoria. He will also deliver a keynote address on managing herbicide residues at the SARDI MAC Annual Field Day in Minnipa (South Australia) on 9 September. These events are supported by the Soil CRC’s Adoption Plan.