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Talking Agronomy with Luke Wheeler: How to end the OSR season

Writing in the middle of June most of the winter and spring crops I walk have received their full spray programme. The next main pass will be desiccation of oilseed rape.


Abby   Kellett

Abby   Kellett

Growth stages of oilseed rape crops will vary depending on variety and also on weather conditions experienced throughout the growing season. It is therefore important to know when your oilseed rape crop is ready to desiccate. With early desiccation resulting in red seed in the sample and potential rejections and late desiccation meaning the crop may have naturally senesced, resulting in poor uptake of the desiccant, it is important to get this timing spot on.

 

Desiccation of oilseed rape is not compulsory and leaving the crop to naturally senesce is an option, although this can lead to a late cut and potential harvest difficulties. When assessing the oilseed rape for desiccation, a sample should be taken from both the central pods of the main raceme and also central pods on the side branches. We are looking for around 60% of these pods to be changing from a green to brown.

 

It may be worth thinking back to the order in which your oilseed rape came into flower as this will likely be the order in which it will need desiccating. Desiccation will likely take place with glyphosate and upon spraying the crop, cutting will normally commence 2-4 weeks later, depending on weather conditions. As glyphosate is related to photosynthesis and therefore crop transpiration, low light levels after spraying will result in a slow kill. High light levels and therefore high transpiration will result in a faster kill. Best timing for glyphosate application is in the morning, ideally on a dew. This allowing the glyphosate to spread across the leaf and giving it the entire day to be taken up by the plant. Avoid spraying in the heat of the day as this will cause the glyphosate to dry fast on the leaf and efficacy will be poor.

 

Desiccating using diquat is another option to growers. Diquat is a much faster acting and means harvest will normally take place 7-10 days after spraying. The correct timing for application of diquat is slightly later than glyphosate and the seed will be at a different stage. The middle third of the canopy should have 90% reddish/brown seeds with some being dark brown/black.

 

The inclusion of a pod sealant with the desiccant is a big discussion point at this time of year. It should be noted that all hybrid varieties have natural pod shatter resistance whereas conventional varieties do not. In areas more prone to hail storms it would definitely be wise to include in the application and inclusion in other areas will be down to both the grower and agronomist. In years when the variation of maturity within fields is very high, it may be worth spraying a pod sealant a week of two earlier than the desiccant. With the variation in field this year not being too high for most, inclusion with the desiccation spray would be fine. This also meaning no extra pass through the crop.


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