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Crop Advice & Expertise

What’s happening in fields across southern central England in November?

Southern central England-based Jon Helliwell talks disease control and interesting trials results in oilseed rape, while blackgrass and aphid control in cereals is also discussed

At a Glance

This month’s update includes information on:

  • Fungicide strategy in oilseed rape
  • Weed control in winter cereals
  • Advice on seed treatments and BYDV control

Cereal

We have generally avoided the worst of the storms in Oxfordshire and Gloucestershire and with soils warm and largely dry, growers have been able to delay wheat drilling until mid- to late-October in good conditions after two flushes of black-grass.

In some areas dry seedbeds have led to concerns about pre-emergence herbicide efficacy and whether to delay application. True pre-emergence is such a critical timing for chemistry and the opportunity for spraying cannot be missed. Black-grass is now starting to emerge in the earliest-drilled crops, which is a worry. In these situations, or when topping up residual combine it with a contact product such as Atlantis (mesosulfuron + iodosulfuron) or Hamlet (mesosulfuron + iodosulfuron + diflufenican).

Interestingly, we have seen impressive contact activity where black-grass has been considerably weakened by the pre-em – it can be the final nail in the coffin – so where the black-grass is at 2 leaf don’t hold off, as fully tillered black-grass in the spring will be much harder to control and result in higher seed return. Bright, clear weather, even in the depths of winter, can give good kill from contact herbicides if sunny conditions are conducive to active growth. If there is a spray window, take it to minimise seed return.

I have had calls from growers about insecticide use for aphid and BYDV control, as although declining, high numbers of bird cherry oat aphids continue to show up in suction traps and crops. Deter (clothianidin) will stop aphids seen in the crop from reproducing and spreading for between 6-10 weeks, depending on drilling date and seed rate.

It is this secondary spread of BYDV which causes the greatest yield loss, so be aware of extended fly in and if we don’t get a prolonged cold spell, some crops may require a follow up pyrethroid spray as seed treatments run out of steam.

Oilseed rape

Oilseed rape has grown away strongly, despite flea beetle pressure increasing further west. Growers have tended to drill earlier often resulting in thick crops with large canopies moving into winter, but have realised the value of good seedbeds and vigorous varieties in achieving positive establishment.

Phoma infection was as early as I’ve seen and it has really helped pick out the varieties with stronger resistance. In more resistant varieties, phoma thresholds frequently haven’t been reached, so one spray with activity on phoma and light leaf spot will suffice on these crops this season.

If applying just one fungicide this autumn, 0.46L/ha of Proline (prothioconazole) is the way to go and the higher rate needs to be maintained to help keep crops protected through to the spring. If a phoma spray with light leaf spot activity has already been applied, it gives some flexibility on rate and timing, with a 0.32L/ha top-up 4-6 weeks after the first application enough to maintain protection through the winter.

Despite the recent cold snap soil temperatures at 30cm are still about 12C, so it is still currently too warm to combine the fungicide with Kerb (propyzamide) applications. If Kerb timings continue to be delayed, don’t be tempted to delay light leaf spot sprays as you risk not getting any protection on at all if the weather deteriorates.

At our Oxfordshire demo site, we have a seed rate and seed treatment trial that has shown some interesting results so far. In part of the trial Elgar sown at 40, 60, 80, 100 and 200 seeds/sq m has seen big differences in rooting and canopy. There has been a trend to drill conventional varieties at higher seed rates due to flea beetle pressure, but lower seed rates clearly produced bigger and stronger roots and look more impressive above the ground, too.

 

OSR

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