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Talking Agronomy with Sam Patchett: Cold weather has really done our oilseed rape crops a favour


Some decent cold weather has really done our oilseed rape crops a favour, shrinking their canopies noticeably as we move into mid-February.

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Even so, green area indices (GAI) across all varieties in our Brotherton iFarm plots are a good 2 or more. Once again the most effective early canopy management looks like being vital for success.


This is underlined by our research into the reasons for disappointingly average 2014 yields from some of the best looking, pod-rich crops of recent years. While winter water-logging and light leaf spot (LLS) infections undoubtedly played their part, our investigations show excessive pod numbers were almost certainly the main culprit in most cases.


Yes, more pods have historically been equated with better performance. But we know seeds/sq.m peak at about 6,000-8,000 pods/sq.m. Yet our assessments reveal many big-canopied crops had almost double this number of pods last season. Taking this on-board, our key priority has to be smaller, more open crops with less flower cover. So we’ll have to be particularly careful with both our early nitrogen and plant growth regulation.


N-min sampling shows all but one of our nine northern iFarms have higher levels of available nitrogen in their OSR soils than this time last year. And we know from their GAIs many of our crops already have a good amount of N in their canopies. This means they’ll need proportionately less early applied N for the optimum 3.5 GAI canopy at flowering.


However, they will still need a good early application of sulphur, posing a dilemma for those using compound fertilisers. For the second year in a row this underlines the value of sulphur provided separately from N, either as polysulphate or kieserite – although generally high levels of Mg from magnesium carbonate liming over many years in our area means we need to be cautious with the latter.


We’ll need to put a lot of emphasis on early plant growth regulation for our OSR too – especially for crops with GAIs of 2 or more. This season we’re able to take advantage of the newly-available specialist PGR, paclobutrazol, which looks like being a valuable improvement on metconazole in this role. However, everyone will need to be conscious of the product’s following crop restrictions – including three years for potatoes.


For the greatest effect on forward crops we’ll be going in with our plant growth regulation as early as we can rather than waiting until green or yellow bud. Where LLS is evident despite good early winter control, we’ll be including prothioconazole in the mix or using tebuconazole + prochloraz and, with soil sampling showing low levels of both micronutrients, adding molybdenum and boron in most cases.


In the past two seasons, we’ve escaped relatively unscathed in terms of pollen beetle. And, if winter doesn’t have a major sting in its tail, our forward crops are likely to come into flower fast and early, minimising our risk once again. Knowing how much damage the pest can do and with pyrethroid resistance at the forefront of our minds, we’ll be taking action wherever thresholds are reached.


Just like our OSR, most of our winter wheats look like coming into the spring in encouraging shape. The late-January/early February cold has been equally valuable for them, although there’s still more than enough septoria about for comfort.


Met Office records show the winter remains noticeably warmer than the 30-year average up here and, more importantly, continues to be more like last year and 2012 than the low disease season of 2013. So we’ll need to be spot on with our spraying.


Our fungicide strategy will be based on different modes of action, with multi-site protectants a core element to counter the triazole shift and protect the SDHIs. We’ll be including at least one SDHI in most of our programmes and doing everything we can to get timings spot on.


Seeing just how much yield can be lost from relatively minor weather or workload-enforced T1 or T2 spraying delays, we’ll be using a timely T0 in most cases to give us the insurance we need in this respect. The average 0.75 tonnes/hectare T0 response we saw across our trials last year underlines just how important the right start is to securing the yields which will give us the lowest possible production cost per tonne.


  • Sam Patchett is an Agrii agronomist based in Yorkshire. He provides agronomy, crop nutrition and seed services to clients growing cereals, oilseed rape, maize and fodder beet across West and South Yorkshire and also helps run Agrii’s Brotherton R&D site near Selby.
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