Crop Watch: Tackle aphids and big blackgrass now

Tackling yield-sapping barley yellow dwarf virus (BYDV), killing big blackgrass plants and making the most of spring fertiliser applications are the key topics being tackled by our Crop Watch agronomists this week.

Both Devon-based Neil Potts and Sussex’s Richard Harding recommend an insecticide in unprotected crops to prevent further spread of yield-sapping BYDV.

See also: Read the full reports from our four agronomists

Mr Harding believes above-average winter temperatures mean it probably has not been cold enough to reliably finish off any lingering aphids in cereals or oilseed rape and they can still be found in some sheltered fields of winter cereal crops.

If BYDV control was compromised last autumn or it has been some time since the last insecticide was applied, take any opportunity to top-up the protection.

Mr Potts is particularly concerned with crops that were drilled without Deter (clothianidin) seed treatment and have not yet received an aphicide for BYDV control.

The expectation is that BYDV will be a clear and present danger to untreated crops, following a winter with little or no frost to kill aphids and, in fact, temperatures high enough for much of the winter to allow continued aphid activity within crop.

“Any crops that have not had an aphicide should receive one as soon as ground conditions allow.”

This may not be enough to prevent BYDV infection at this stage, but it should help to prevent further spread within the crop, he adds.

Big blackgrass

In Yorkshire, David Martindale has seen many spray recommendations missed at the back end of last year, allowing blackgrass to thrive in some crops.

In winter wheat, pre-emergence residual herbicides have worked well and where follow-up herbicides were applied last autumn, overall blackgrass control is good.

For remaining crops, it is a case of switching to plan B and contact-acting herbicides such as Atlantis (iodosulfuron + mesosulfuron) to try to finish off the remaining blackgrass.

However, with the winter so mild, blackgrass has kept on growing like the crops, so is now well tillered. Applying these contact-acting herbicides in good growing conditions is crucial to try to maximise efficacy.

Fertiliser plans

Farmacy adviser Ryan Hudson has had some soil analysis results back and soil mineral nitrogen (SMN) is at a similar level to last year in his region, generally between 50kg/ha and 70kg/ha of nitrogen, with slightly higher levels after oilseed rape and beans.

Crops are also quite variable, with some oilseed rape at green area index 2.0 and above, resulting in about 100kg/ha of nitrogen already in the plant.

Taking the SMN, crop growth and likely mineralisation, rates have been adjusted to ensure we are applying optimum nitrogen.

As and when conditions allow, nitrogen is being applied to the more backward oilseed rape, barley and late-drilled and second wheats. The nitrogen on some of the more forward oilseed rape will be held back a little yet.

NOVEMBER
3

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