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With many oilseed rape crops having a prolonged flowering period due to cool weather in April and May, it will be particularly important not to apply a desiccate too early this season to avoid reducing yield and oil content.

ADAS crop physiologist Pete Berry says this season's conditions have been good for seed setting and crops could have high yield potential. "To realise this, it will be vital that all seeds are well filled by maximising the duration of seed filling and not desiccating too early.

"Seed filling in oilseed rape lasts for about 40 days and each lost day would lead to about a two per cent reduction in yield. Most oil is formed in the seed during the second half of seed filling, so anything that curtails this period will reduce oil concentration."

Not all crops need desiccating; it may not be necessary in dry summers or if an early developing variety is grown. Where desiccation is required, a pod sealant could help to avoid having to desiccate too early, says Mr Berry.

Slow acting

Glyphosate is slow acting and the crop is usually ready for harvest 2-3 weeks after application, he says. "Check the label advice for when best to apply glyphosate, but in general it should be done when two-thirds of the seeds in 75 per cent of pods picked from the centre of the main raceme have turned brown."

Early application timing can also increase the chance of red seeds due to uneven ripening, warns Hutchinsons' Dick Neale. "Any more than five per cent and the crop will face rejection.

"The best guide for when the crop is ready is the overall crop appearance and seed colour - the crop canopy should resemble the colour of a hare's back."

As far as tools for desiccation go, glyphosate is now the only chemical option following the loss of diquat, says Mr Neale.

"However, remember that glyphosate cannot be used on seed crops. It is best to aim for application 14-20 days before harvest. Seed moisture should be at 30 per cent or below for glyphosate application."

Growers should also factor in conditions when spraying, says Bayer's Matt Siggs. "Time of day can affect Roundup performance. If possible, spray earlier in the day. Higher humidity means the plants' stomata are open which improves penetration and product efficacy."