February 23, 2015
Crucial canopy care
Some decent cold weather has really done our oilseed rape crops a favour, shrinking their canopies noticeably as we move into mid-February. Even so Green Area Indexes across all varieties in our Brotherton iFarm plots are a good 2.0 or more. Once again then, 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 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/m2 peak at around 6000-8000 pods/m2, mainly because dense, prolonged flowering seriously reduces the amount of light reaching the leaves and stems for photosynthesis in the critical 2-3 weeks from mid-flowering. 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 that 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’ll 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 nitrogen, 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 2.0 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 light leaf spot is evident despite good early winter control, we’ll be including prothioconazole in the mix or using tebuconazole + prochloraz (all of which have performed extremely well in HGCA trials) 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 from 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 from this quarter once again. Knowing how much damage the pest can do and with pyrethroid resistance at the forefront of our minds, though, we’ll be taking rapid 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 firmly based on different modes of action, with multi-site protectants a core element to counter the triazole shift and protect the SDHIs that have proved so effective in Septoria control. We’ll be including at least one SDHI in most of our programmes and doing everything we can to get timings spot on.
Seeing from our research 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 t/ha T0 response we saw across our national trials network last year underlines just how important the right start is to securing the yields that will give us the lowest possible production cost per tonne.
You can email Sam your comments and opinions via firstname.lastname@example.org.