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Talking Agronomy with Sarah Symes: Crops are responding to warmer weather

The Easter Bank Holiday confounded all expectations and temperatures reached a tropical 21 degrees here in parts of the South.

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Sarah Symes
Sarah Symes

Forward oilseed rape varieties such as Charger were on the verge of flowering at the end of March, perhaps quicker than expected, so green/yellow bud sprays were programmed in and crops were easily waist height by the start of April. Many of my farmers hadn’t long applied the light leaf spot spray, which was recommended in February, so in these instances there will be a mid-flowering spray instead of an early- and late-flowering spray. In the rare case we had to spray for pollen beetle in April, Plenum (pymetrozine) or Biscaya (thiacloprid) were used due to pyrethroid resistance.


Now the soil temperatures have warmed up we are also seeing fresh flushes of charlock and cleavers, but sadly crops are now beyond the growth stage to be able to do anything about it but the crop canopies should smother them.


We will be monitoring for seed weevil which can lead to pod midge issues and a low rate of Hallmark (lambda-cyhalothrin) will be recommended only if the threshold for seed weevil reaches one-teo weevils per plant and not just on the headland. If we need to add an insecticide at the mid-/late-flowering stage we will need to ensure pyrethroids and triazoles are not mixed as this could be dangerous to bees.


Our earliest T0 applications were applied over Easter weekend, crops are still looking clean, with only septoria on older leaves, so Bravo (chlorothalonil) has in many cases been the only fungicide in the mixture, variety dependent. T1s are being applied now and will, in nearly all cases, be an SDHI in mixture with Bravo again.


Wild oat and cleaver control has also been incorporated where needed. It’s important to apply T1s at the correct timing, not only for leaf 3 protection but to not give a too larger gap between a T1 and T2 applications where leaf 2 would normally be left out, if the gap is looking to be more than three weeks between applications it may be worth considering a T1.5 to ensure good cover on leaf 2. T2s will also require a robust strategy, and like last year we will be taking advantage of SDHI chemistry for protection against septoria and rusts. T3s are being planned for the early June, which will consist of prothioconazole and tebuconazole for protection against Fusarium strains which can lead to mycotoxins.


Winter barley has steamed ahead with the warm weather at the start of April and most crops have got a second fungicide application in the pipeline, which will be applied no later than four weeks after the first fungicide application and may have just received a separate application of Terpal or Upgrade (both 2-chloroethylphosphonic acid + mepiquat chloride) to prevent brackling.


Rhyncosporium started to make an appearance at the end of March, as did mildew and rust in forward crops, so a mildewicide was added to the growth regulation and first SDHI fungicide.


Spring beans are coming through the ground well after a slow start and pre-emergence sprays have been applied. With the warmer weather, it is prime time for pea and bean weevil activity, at the first signs of notching on the leaves a pyrethroid will be applied. For any broad-leaved weeds which escaped the pre-emergence mixture, depending on weed spectrum, bentazone will be applied with a mineral oil.


Spring barley generally went into good seedbed conditions and pre-emergence sprays were applied soon after drilling. Many crops came through the ground quickly and are growing away well, with all nitrogen and sulphur applied. Our attention will now turn to weed and disease control.


Maize ground is being prepared and Stomp Aqua (pendimethalin) pre-em sprays planned in for when crops are in the ground. In many cases DAP will be placed down the spout, and nitrogen rates increased to 150kgN/ha as research has showed maize crops will benefit in yield from higher nitrogen applications and this is the most nitrate vulnerable zone regulations will allow.



  • Sarah Symes is an independent agronomist working with the Hampshire Arable Systems partnership. Based in Hampshire, she advises clients growing cereals, oilseed rape and pulses
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