DEKALB trials manager, Anders Christensen assesses OSR development at flowering from the company’s network of 25 trial sites in the third of our special series.
Compensation is key to overcoming crop variability
OSR performance this season will depend as much on crops’ ability to compensate for the challenges of a cold start and aggressive late pigeon grazing – not to mention damage from flea beetle larvae – as anything else.
Long-awaited spring warmth worked wonders for crop growth and development. But, as I write in early May, flowering is only peaking in much of the country and just starting in Scotland.
As well as lateness, variability is the one thing defining this year’s crops. Some are chest high and others barely up to the waist. And some plants in some parts of a field are in full flower while others in other areas are just starting to yellow-up.
Some crops seem to be having the short, sharp flowering that really helps light interception and sclerotinia management. But for those trying to recover from earlier setbacks, it could well be a far more prolonged affair, putting the onus on the most effective flowering spray programmes.
DK Extrovert, DK Expedient and DK Exalte are continuing to stand out for their earliness in our 27-variety trials set. Averaged across our English sites, all three have earliness of flowering scores a good one point (on a 1-9 scale) ahead of last season’s RL leader, included for comparison.
Amongst the Clearfield varieties, DK Impressario CL is maintaining its earliness advantage.
What’s more, two promising new HOLL varieties are looking well ahead of the V316OL benchmark.
Interestingly too, we are seeing clear differences in the growth habit of the low biomass (semi-dwarf) hybrids we are testing, two of them coming into flower noticeably earlier than the other and the fastest developer being almost up with DK Exalte.
All our varieties have coped well with flea beetle larvae pressures, which seem to have declined markedly in previous hotspots for the pest. In areas where we have recorded more 50 larvae/plant in the past, for instance, we haven’t found 15 larvae per plant this season.
While nowhere near this level, our monitoring suggests other parts of the country are seeing a general increase in flea beetle larvae levels which may be further contributing to crop variability.
Early pod set looks to have been generally good across the country, although again we are seeing a fair degree of variability – almost certainly due to the stress many crops have been under.
This variability makes the superior ability of the best hybrids to compensate with more extensive podding in better-branched canopies more welcome than ever; especially if limited crop growth in the cold spring means a greater availability of nitrogen for pod fill.
It will, however, be crucial to give crops enough time to compensate ahead of harvesting. We know that every day of pod fill lost reduces yields by 1-2% and most oil is accumulated in the second half of pod filling. So the last thing crops will need this season is desiccating too early.
Glyphosate spraying needs to be timed to the maturity of the pods in the part of the canopy bearing the lion’s share of the yield. This may be up to a week later than main raceme ripeness but, with pod shatter resistance cutting the risk of seed loss from more mature pods, sufficient patience will be well-rewarded.
Minimise seed losses with pod shatter resistance
Seed losses of as much as 0.5t/ha can be saved in the normal run-up to harvesting with genetic resistance to pod shattering, reveal the latest trials run for us by ADAS.
Their replicated trials last season involved nine leading varieties in commercial use, with standard laboratory shattering tests conducted on three separate occasions from the end of June – at 10%, 50% and 90% pods ripe respectively.
In parallel to this, they measured natural seed losses using aluminium trays laid beneath the variety plots three weeks prior to planned harvest and removed just ahead of combining.
Even at 10% of pods ripe, shattering was significantly higher in susceptible varieties than in those with DEKALB pod shatter resistance. These differences became more apparent with increasing pod maturity so that at 90% ripeness shattering in our resistant varieties was typically less than half that in the non-resistant ones.
Significant differences in natural pre-harvest losses were also quantified; shatter susceptible varieties losing the equivalent of 0.23-0.57t/ha ahead of combining against the 0.1t/ha or less lost by those with pod shatter resistance.
This work supports the variety differences highlighted in previous John Innes Centre random impact testing and NIAB/TAG delayed harvest trials which identified a yield gap of 6-9% between shatter resistance and susceptible varieties of the same genetic potential with combining delays of 7-14 days.
It underlines the value of a high level of natural protection against seed losses ahead of combining under normal circumstances, not to mention particularly heavy rain and hail storms. Shatter resistance also allows harvesting to be timed to secure the highest outputs from well-structured canopies at the least risk of losing seed from over-ripe upper pods. And it even enables quality wheats to be prioritised for combining ahead of OSR without undue worry should the need arise.