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Pre-Harvest and Desiccation Option Update – Mid August 2020

14 August 2020

If using a pre-harvest spray with glyphosate in cereals, remember to adhere to the recommended timing – not to treat before crop grain moisture has fallen below 30%.

Treating earlier than this increases the likelihood of residues in the grain. In weedy crops or those with secondary growth as seen this year, there is a proven benefit from pre-harvest glyphosate, particularly if the weather turns wetter. For clean cereal crops there is generally no proven benefit, although trials have shown a small benefit in spring barley. Check with the end user and do not treat seed crops.

Combine peas

Due to the indeterminate nature of combining peas, crops in Scotland generally benefit from a pre-harvest spray.

Glyphosate is recommended as a pre-harvest herbicide and any desiccating effect is an additional benefit. Crops grown for seed should not be treated with glyphosate.  As the crop is almost mature when glyphosate is applied, this treatment does not accelerate the natural rate of crop maturity; it should not be used to even up or desiccate peas. The recommended dose of glyphosate for weed control in peas varies according to the product used, weeds that are present and their density. The average moisture content of the seeds should be below 30%. The target weeds should be healthy with green leaf to intercept the spray. Harvest may take place 7 days after application of glyphosate but 10-14 days is more likely.

Field beans

Field beans for animal feed can be treated pre-harvest for control of most grasses and broad-leaved weeds with many glyphosate products.  It is applied when seed has below 30% moisture, the bean stems are usually green/brown and the pods are black. This is generally about 10-14 days before harvest, but can be a lot longer. Later in the autumn crops can desiccate naturally once night time temperatures fall.

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