2014-06-23   facebook twitter rss

Time your OSR Desiccation with care this Season

Don’t rush into desiccating your winter oilseed rape this season. The optimum glyphosate spray timing for well-structured modern hybrids is significantly later than for traditional, denser pure line stands.

Holding off with the sprayer will not delay combining and could make all the difference in maximising yields and oil contents from this year’s high potential crops. What’s more, today’s pod shatter resistant varieties mean this can be done without increasing the risk of seed losses in the run up to and at harvest.

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This is the firm advice of Roundup technical specialist, Manda Sansom who finds that the desire to avoid interfering with the wheat harvest often tempts growers into desiccating their OSR too early; especially so under the pressure of acute workload and weather worries.

“Unlike last year, we have time this season,” she pointed out. “Particularly where early maturing varieties like Excalibur and DK ExPower are being grown. We also have even, well-structured crops which will benefit from extra time for pod-filling and oil accumulation. And, in most cases, quite enough moisture in the ground to support it.

“Combined with continuing nitrogen uptake – especially after late fertiliser applications – and robust sclerotinia treatments, this season’s thick-stemmed, well-branched crops, of course, will naturally stay green longer. All of which makes it more important than ever to use a quality glyphosate at the best possible timing.

“Our work clearly shows that earlier desiccation does not mean earlier combining,” Mrs Sansom stressed. “Desiccating too early just means stems take longer to dry down. It may also noticeably restrict output – primarily by limiting the oil that is formed relatively late in seed-fill – as well as increasing the risk of red seed at harvest.”

Monsanto studies also confirm that the far greater branching of modern hybrids grown at today’s recommended plant populations means a much higher proportion of the crop yield comes from side branches which mature significantly later than the main raceme.

Indeed, crops with average populations of 30-40 plants/m2 were typically found carry 80% or more of their yield in side branches which had seeds with a 5% higher moisture content than those on the main raceme.

“Desiccating these sort of crops when the seeds on the main raceme are at the right stage of ripeness – as has always been advised for traditional pure line stands – would clearly be premature,” observed Manda Sansom. “After all, at a time when just eight out of the 45 pods (18%) on the main raceme were immature, on an entire plant with five shoots we have recorded 43 of its total of 143 pods (33%) as immature.

“With 10 good pod-bearing branches or more on many crops this season, spray timing needs to be based on assessments of pods from the area of the crop where the bulk of the yield is being carried, not the main raceme. In many cases this may 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,” she accepted. “But any losses from here will be minor compared to the yield, oil and sample quality gains from the entire crop. And genetic pod shatter resistance will be extremely valuable in limiting even these possible losses.”

In practice timing can only be determined by taking a representative sample of 20 pods and when the colour in the majority of the seeds changes from green to brown the crop has reached the threshold of 30% seed moisture.

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

As well as modern Roundup brands which offer the most efficient activity through more reliable uptake and translocation under the particularly challenging conditions of a heavily-waxed and senescing crop, she recommends:

  • Using water volumes of 200-250 litres/ha in thick or leaning crops

  • Spraying early in the day in hot weather to take advantage of higher relative humidity

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

  • Employing low drift nozzles or formulations wherever possible.


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