Glyphosate residues in canola
Food safety is an increasing concern in many of our key export markets, including the risk of chemical residues entering the supply chain. To help protect and maintain the reputation of Western Australian growers as suppliers of clean, safe grain, CBH tests for chemical residues during and after harvest. This ensures that grain in the supply chain complies with the relevant Australian Maximum Residue Limit (MRL) and can be supplied according to customer specifications.
Europe is a key export market for Western Australian canola and the European glyphosate MRL of 10 mg/kg is half of the Australian MRL of 20 mg/kg. CBH carefully monitors glyphosate residue in all canola stacks to ensure that all canola supplied is below the destination country MRL. Growers can minimise residues in grain delivered to CBH by considering the rate and timing of glyphosate applications to canola.
Roundup Ready (RR) and Truflex canola are tolerant to glyphosate. However, it is important to comply with all label instructions around application timing and product rate. Specifically, for Truflex canola, glyphosate can NOT be applied from the period from BBCH61 to 20% seed colour change. For RR canola this period extends out from the 7-leaf stage to 20% seed colour change. Glyphosate applied during this period can result in residues that exceed the Australian MRL.
A field trial conducted in Quairading in 2023 (Figure 1) demonstrated that glyphosate applied prior to the label application timing resulted in higher residues than when applied as per label at 20% seed colour change. It is important to note that 2023 had a hot, very dry finish to the growing season, and that residues could be significantly higher in a cooler finish with greater rainfall. The plants must be senescing when glyphosate is applied, and a softer finish can result in plants remaining greener for longer allowing more glyphosate to be translocated to the seed.
The 20% seed colour change growth stage is the critical timing for pre-harvest application of glyphosate to canola. This assessment should be conducted on the LEAST MATURE part of the paddock. To identify when a crop reaches the 20% seed colour change stage, remove pods from various heights along the main stem and branches of canola plants and peel them open. Seeds in pods at the bottom of the plant should be brown-black. The seeds from the pods in the middle of the plant should be beginning to change colour with 20% or more being black, brown with some speckled while those at the top of the plant can still be green but should be firm to roll and not watery or mushy. Overall, there should be a minimum of 20% of seeds that are brown-black in colour.
Minimising Glyphosate Residues
- Only apply glyphosate when required, avoid a spray it anyway approach.
- Consider using diquat (e.g. Reglone®) as an alternative.
- Always follow the product’s label for application rate, timing and withholding period (WHP).
- Apply the lowest label rate applicable.
- Do NOT apply prior to 20% seed colour change.
- Seek advice from your agronomist.
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Ask our AgronomistContact CBH's Agronomist Steven Tilbrook
if you would like more information about this topic.Steven Tilbrook
T: 0447 370 049
E: Steven.Tilbrook@cbh.com.au