Arable News

  • Written by: Farmers Guide
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Time your OSR desiccation with care

Dontrush into desiccating your winter oilseed rape this season. The optimumglyphosate spray timing for well-structured modern hybrids is significantly laterthan for traditional, denser pure line stands. Holding off with the sprayerwill not delay combining and could make all the difference in maximising yieldsand oil contents from this years high potential crops. Whats more, todayspod shatter resistant varieties mean this can be done without increasing therisk of seed losses in the run up to and at harvest.

Thisis the firm advice of Roundup technical specialist, Manda Sansom who finds thatthe desire to avoid interfering with the wheat harvest often tempts growersinto desiccating their OSR too early; especially so under the pressure of acuteworkload and weather worries.

Unlike last year, we have time this season, she pointed out. Particularlywhere early maturing varieties like Excalibur and DK ExPower are beinggrown.  We also have even,well-structured crops which will benefit from extra time for pod-filling andoil accumulation. And, in most cases, quite enough moisture in the ground tosupport it.

Combined with continuing nitrogen uptake especially after late fertiliserapplications and robust sclerotinia treatments, this seasons thick-stemmed,well-branched crops, of course, will naturally stay green longer. All of whichmakes it more important than ever to use a quality glyphosate at the bestpossible timing.

Ourwork clearly shows that earlier desiccation does not mean earlier combining,Mrs Sansom stressed. Desiccating too early just means stems take longer to drydown. It may also noticeably restrict output primarily by limiting the oilthat is formed relatively late in seed-fill as well as increasing the risk ofred seed at harvest.

Monsanto studies also confirm that the far greater branching of modern hybridsgrown at todays recommended plant populations means a much higher proportionof the crop yield comes from side branches which mature significantly laterthan the main raceme.

Indeed,crops with average populations of 30-40 plants/m2 were typically found carry80% or more of their yield in side branches which had seeds with a 5% highermoisture content than those on the main raceme.


Desiccatingthese sort of crops when the seeds on the main raceme are at the right stage ofripeness as has always been advised for traditional pure line stands wouldclearly be premature, observed Manda Sansom. After all, at a time when justeight out of the 45 pods (18%) on the main raceme were immature, on an entireplant with five shoots we have recorded 43 of its total of 143 pods (33%) asimmature.

With 10 good pod-bearing branches or more on many crops this season, spraytiming needs to be based on assessments of pods from the area of the crop wherethe bulk of the yield is being carried, not the main raceme. In many cases thismay mean desiccating 7-10 days later than would otherwise be the case.

The upper pods on the main raceme may be over-ripe by this stage, sheaccepted. But any losses from here will be minor compared to the yield, oiland sample quality gains from the entire crop. And genetic pod shatterresistance will be extremely valuable in limiting even these possible losses.

In practice timing can only be determined by taking a representative sampleof  20 pods and when the colour in themajority of the seeds changes from green to brown the crop has reached thethreshold of 30% seed moisture . A detailed timing guide is available at


While desiccation will be more rapid andcomplete when undertaken at the right stage of crop maturity, Mrs Sansom isadamant it will continue to demand the most effective glyphosate regime.

Aswell as modern Roundup brands which offer the most efficient activity throughmore reliable uptake and translocation under the particularly challengingconditions of a heavily-waxed and senescing crop, she recommends:

  • Usingwater volumes of 200-250 litres/ha in thick or leaning crops;

  • Sprayingearly in the day in hot weather to take advantage of higher relative humidity;

  • Adjustingthe boom to ensure the best spray pattern coverage of the whole crop; and,

  • Employinglow drift nozzles or formulations wherever possible.


  • Written by: Farmers Guide
  • Posted:
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