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Winter Oilseed Rape – Harvest management

7 August 2019

Swathing can have a place in exposed sites so long as it is not a wet field.  The optimal timing for swathing is when the colour of seed is green to green-brown in the top pods, mainly red-brown in the middle pods and dark-brown in the bottom pods.  AHDB trials have shown that mistimed swathing can significantly reduce oil content.  Make sure the swather is cleaned and free of grass weed seed contamination – swathers have been known to spread problem grass weeds.

The majority of crops these days are desiccated, often with glyphosate because as well as desiccating the oilseed rape, it clears up any patches of perennial weeds giving a clean start for the next crop.  As a general rule aim to apply 1080g/ha a.i. glyphosate for desiccation and increase to 1440g/ha if targeting perennial weeds.  It is best to spray early in the day when humidity is higher and to keep the water volume up to achieve good penetration of the canopy.  Correct timing is important – trials have shown no benefit from treating before the recommended time, in fact, it can mean stems take longer to dry out and oil content is reduced.  A representative sample should be taken to include side branches as well as main stems.

The earliest timing for glyphosate is when more than 66% seeds are green/brown as shown, and all seeds below 30% moisture content.  The harvest interval is 14 days, although it may be up to 3 weeks before the crop is ready to cut.
Diquat (Reglone) is the alternative to glyphosate, and is a faster acting desiccant.  It is the preferred option in severely lodged or uneven crops.  However, wrongly timed diquat can desiccate the pods, leaving green stems and can give rise to shattering losses if the harvest is delayed – otherwise, it is the quickest to harvest.  It also has the advantage of being rain fast in about 15 minutes.  Diquat should be used with a non-ionic wetter.  Timing for diquat is as follows:

Timing for use of diquat in winter oilseed rape

Point in CanopySeed Colour in Pods
TopMore than 50% green
Mid90% red-brown/black-brown, the rest firm & pliable
BottomAll dark-brown to black

Remember to use up any stocks of diquat products – all are under revocation with use-up by 4 February 2020, and oilseed rape is one of the limited range of crops that can still be treated with diquat.

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