Sunday, November 19, 2017

Newly drilled crops require care this autumn

October 4, 2017 by  
Filed under Crops

RichardOverthrow2013A

A catchy harvest led to a catchy drilling season but at least that suggests some consistency, writes Richard Overthrow.

Hopefully, most of the autumn crops are in now with only winter beans and late sown wheat, due to grass weed pressure or late harvested root crops, left to go in. Remember to adjust seed rates for these late cereal sowings, particularly if delaying due to grass weeds.

This approach only works if the crop is competitive from the off so needs to establish and cover the ground fairly promptly. October sowing increases the likelihood of rainfall and hence moist seedbeds to get the best out of residual herbicides, another advantage in delayed sowing.

Growers without grass weed problems should still aim for autumn treatment of broadleaved weeds because treating when target plants are small will make herbicides more effective and allow growers to reduce doses.

Slug monitoring should continue, as many cereal crops start to emerge. Remember to follow stewardship guidelines, particularly if using metaldehyde. Ferric phosphate products are as effective as metaldehyde and should be considered particularly where there is a risk of run-off or other means of water contamination should metaldehyde be used.

Aphid activity

BYDV control programmes will be ongoing, protection is needed until the end of aphid activity, typically in early November. Make sure insecticide protection covers the crop until that point. Deter seed treatments can protect the crop for up to six weeks after drilling but if this doesn’t cover the whole risk period then follow-up sprays will be needed.

However, recent mild autumns showed us that protection may be needed well after the end of the flight period, even if aphids have stopped flying-in. If such conditions return this autumn then a more robust approach to insecticide protection will be needed.

In oilseed rape, cabbage stem flea beetle numbers were variable this year but quite serious in some areas: next comes the larva problem, which doesn’t seem to relate to adult numbers anyway. There are no control options against the larvae unfortunately and the only option is to leave alone and hope the crop comes through any infestation.

Rape crops should also be monitored regularly for the arrival of the first phoma lesions. First sprays should be applied when the threshold is reached (one plant infected in ten, or one in five for resistant varieties).

If sprays need to be applied at the start of this month then a follow-up is likely to be needed if new lesions arrive later in autumn. If the first spray isn’t applied until the end of this month then it will likely protect the crop for the infection risk period, and should cover as an autumn treatment for light leaf spot.

Cereal volunteers

Early cereal volunteer sprays will have been applied to young rape crops but second graminicide sprays for grass weeds may be applied this month. Remember if two ACC-ase graminicides are applied to a crop, they must be different active ingredients targeting different weed species.

Carbetamide and propyzamide are popular post-emergence residual herbicides. Both need soil temperatures to fall to certain levels before they are applied, though recent trials have shown that a sequence of the two can be effective against difficult black-grass populations.

Applying carbetamide in the early part of this month with propyzamide at its more traditional later timing would be particularly useful where there is known to be significant resistance to foliar graminicides (ACC-ase inhibitors).

Winter bean crops can be sown from the middle of this month. Early sowing should be restricted to the shorter varieties as the crop responds quite markedly to sowing date in terms of final crop height and therefore lodging risk.

Richard Overthrow is a regional agronomist with NIAB TAG, the UK’s largest independent agronomy organisation with several research centres. For more details call 01223 342495.

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