Pre-harvest glyphosate: best practice in cereals
In cereals, glyphosate applications can reduce green material, including immature tillers, and improve harvest efficiency and grain storage. This can be particularly valuable in wet seasons. Glyphosate residues are occasionally found in samples. Although these residues have been well below Maximum Residue Levels (MRLs), they require careful management.
Glyphosate residues and cereals
Although glyphosate residues have sometimes be found in bread samples, these residues have been well below Maximum Residue Levels (MRLs), according to information published by the UK Expert Committee on Pesticide Residues in Food (PRiF). In 2016, for example, the mean level in wholemeal bread was 8% of the MRL and in other bread was 13%. The precise incidence in home-grown milling wheat is not clear, as UK bread can contain imported wheat. It is, however, essential to follow best practice to minimise glyphosate residues in cereal products.
Glyphosate application timing is critical
Only use glyphosate when the grain has less than 30% moisture content. This coincides with the ‘hard dough’ stage (Growth Stage 87) of grain maturity and normally occurs one to three weeks prior to harvest. Use the following visual tests to guide whether a crop is at or below 30% moisture content:
- The peduncle test (wheat and barley): When the peduncle, situated at the top of the stalk (immediately below the ear), starts to lose its green colour and turns brown.
- The thumbnail test (wheat, barley and oats): When a thumbnail indentation holds on 20 grains collected from various areas in the crop (from the centre of each ear).
- The split grain test (wheat): When grains are cut in half and 75% have a dark brown pigment strand in the crease, the grain has reached 30% moisture. If all the grains are marked, moisture content is estimated at below 30%.
All estimates should be confirmed using a moisture meter.
The statutory harvest interval is seven days. Some crops, particularly wheat, may require up to 14 days for the glyphosate to be fully effective. This longer interval is more likely under dull and overcast conditions and/or when broad-leaved weeds are present.
Target weeds should be green, healthy and actively growing. Weeds that have senesced, died back or are suffering from drought may not be as susceptible. Ensure the dose is matched to the weed species present (check the product label).
- When used in accordance with the label, glyphosate may be applied to crops used for feed and to wheat and oat crops intended for milling and to barley intended for malting. Always check your contracts, however, as some end users may restrict glyphosate use
- Do not use glyphosate in crops grown for seed production or in undersown crops
- Do not use glyphosate-treated straw as a horticultural growth medium or mulch. Treated straw, however, may be used for animal feed or bedding
- Ensure the sprayer boom is adjusted in height so the spray pattern covers the target weeds correctly