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Stackyard News Jul 06

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OSR Harvesting Trials Highlight Desiccation Flexibility

Desiccation with glyphosate offers oilseed rape growers greater flexibility to avoid the losses in both oil content and yield that can result from swathing too early, according to newly published HGCA trials run by the Arable Group.

oilseed rape

Eight trials at three sites over the past three years, compared swathing and desiccation at two different timings before harvest in the same variety (Royal) to examine the impact of harvesting technique on oil content.

Desiccation five days earlier than the ideal seed stage (typically 18-21 days before harvesting) produced oil contents of 42.5% and oil yields of 1.63 t/ha on average. In contrast early swathing produced oil contents of 42.0% and yields of 1.48 t/ha.

The timing of desiccation with glyphosate had noticeably less impact on oil content and yield than the traditional harvesting method, with swathing five days before the ideal stage producing oil contents 0.2% and oil yields 0.07 t/ha down on swathing later.

Table: Effect of Pre-Harvest Treatment on Oil Content and Yield (2003-2005)

Harvesting Technique

Oil Content (%)

Oil Yield (t/ha)

Glyphosate desiccation 5 days before ideal stage



Glyphosate desiccation 3-5 days after ideal stage






Swathing 5 days before ideal stage



Swathing 3-5 days after ideal stage



“The effects of pre-harvest treatment varied between sites and seasons,” comments TAG’s, Stuart Knight. “And in some cases higher seed losses through harvest delays were partly responsible for lower seed yields from early swathing.

“Nevertheless, our results highlight that some growers may be missing out in seed yields and oil contents by swathing too early in an attempt to avoid the risk of shedding losses through cutting too late.

“Desiccation with glyphosate appears to be a more time-flexible technique that may be particularly valuable for those pressed for time around harvest. After all, the difference between swathing and desiccation at the same early timing in our trials was 0.5% oil and 0.15 t oil/ha. Which is certainly worth having with oil bonuses as they are.

“Variety selection and crop nutrition undoubtedly have more significant effects on oil content than harvesting technique,” he stresses. “But, as they say, every little helps.”

Commenting on the TAG findings, Monsanto technical specialist, Manda Sansom adds that using Roundup to desiccate oilseed rape will cost less than half the typical £32-35/ha cost of swathing, further adding to the financial benefit of any oil content advantage.

“Bear in mind too that if you grow low biomass varieties you won’t need a contractor with high clearance equipment to do the spraying either, giving you valuable extra flexibility to optimise harvest timing as well as useful extra savings.

“Lower combining costs, greater combining efficiency, reduced weather dependency, lower drying costs and valuable weed control are further well-established benefits of desiccation,” she notes. “Growers must, however, be aware that they should not use pre-harvest glyphosate on seed crops.”

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