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BEST PRACTICE - OILSEED RAPE DESICCATION

TOP TIPS

  • Spray as soon as the majority of the crop reaches 30% seed moisture to maximise efficacy and minimise residues. See timing details below
  • Use Roundup brands for the most efficient activity through more reliable uptake and translocation under the particularly challenging conditions of a heavily-waxed and senescing crop.
  • Use the correct label rate- never exceed the maximum label rate Pod sealants can be mixed with Roundup, but the timing and application must still meet Roundup label specifications.
  • Use water volumes of 200-250 litres/ha in thick or leaning crops;  
  • Using angled nozzles to increase penetration into thick crops.
  • Spray early in the day in hot weather to take advantage of higher relative humidity;
  • BEWARE: When spraying tall crops pre-harvest there is increased risk of drift damage to hedgerows & glyphosate- sensitive crops like seed potatoes, fruit and vegetables.
  • Follow spraying Best Practice, choose low drift nozzles and a modern Roundup brand with low drift properties  
  • Adjust the boom height to ensure the best spray pattern coverage of the whole crop;  
  • Follow the minimum harvest interval of 14 days

TIMING

The desire to avoid interfering with the wheat harvest often tempts growers into desiccating their OSR too early; especially under the workload pressure and weather worries.

It is really important to get the timing of oilseed rape desiccation just right. It is not an easy decision and cannot be done by assessing crop colour changes from the gate.

30% seed moisture will always be an average for oilseed rape which is a non-determinate plant. So when the average moisture is 30% there will be proportion of plant which flowered last where seed moisture is above 40% and the seed is still filling.

Desiccation too early risks both limiting oil percentage, (formed relatively late as the seed fills), and increasing the risk of immature red seed at harvest.

NB. Studies confirm glyphosate residues in the rape plant will not be found in the extracted oil. The majority, 85%, will be in the straw and the remaining 15% in the cake.

The optimum glyphosate spray timing for well-structured modern hybrids is significantly later than for traditional, denser pure line stands.

Going in too early does not speed up the process and could make all the difference in maximising yields and oil content from high potential crops. With Dekalb pod shatter resistant varieties this can be done without increasing the risk of seed losses in the run up to and during harvest.

Combined with continuing nitrogen uptake from late fertiliser applications and robust fungicide treatments, thick-stemmed, well-branched crops, will naturally stay green longer.

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

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 crops when the seeds on the main raceme are at the right stage of ripeness would clearly be premature. 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 necessarily the main raceme. In many cases this may mean desiccating up to 7 days later than conventional timing.

The upper pods on the main raceme may be over-ripe by this stage, but any losses from here will be minor compared to the yield, oil and sample quality gains from the entire crop. Genetic pod shatter resistance will be extremely valuable in limiting 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.

Download your copy of the Harvest Management Timing Guide here