Wednesday, February 26, 2020

When timing is (almost) everything for crops

October 1, 2019 by  
Filed under Crops

Drill timing has an increasingly important role in combating pests, diseases and grassweeds, says Richard Overthrow.

It will be some time before we know the final acreage of winter oilseed rape this season as for many in this area the drilling window extended from late July to late September.

Many crops were still lost to flea beetle, as before, and it’s not clear yet if sowing date had any influence. Generally insecticide sprays had little effect, but if you have an established rape crop the agronomy issues continue for some time yet.

Any surviving rape crops should still be monitored regularly for the arrival of the first phoma lesions, though if none has appeared yet we are close to the standard autumn fungicide timing so a single treatment soon (prothioconazole is the best option) will control any subsequently-arriving phoma as well as any autumn light leaf spot infections.

If phoma has already been treated it will have been too early to ‘close the gate’ and the standard timing should still be adhered to, though in such cases, unless phoma comes back quickly, this could be delayed until early next month.

Most 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.

Centurion Max is commonly used, but check the manufacturer’s guidelines for use with respect to tank mixing and spray intervals.

Post emergence

Propyzamide and carbetamide are commonly-used post-emergence residual herbicides and where pre-emergence treatment is avoided in flea beetle campaigns, may follow applications of Belkar, in which case these follow-ups won’t be particularly urgent. Both residuals need soil temperatures to fall to certain levels anyway before they are applied.

The bulk of winter wheat sowing is likely to be done this month, as an ever-decreasing acreage is sown in September. This is no longer solely due to grass weed issues, BYDV and other diseases are also urging drilling delays.

BYDV is always unpredictable and although its effects can be severe, we must avoid placing the crop in a situation that demands multiple insecticide treatments.

Cereal crops sown in the first half of October should only need one BYDV spray, any sown in late October may not need any treatment if it hasn’t fully emerged by the end of the first week in November. The accumulated thermal time system will be a useful guide to timing of first and, if needed, subsequent treatments.

Cereal drilling is therefore ongoing and for most there has been sufficient rainfall to allow reasonable seedbeds to be prepared. Crop establishment should therefore be fairly prompt and even.

Where residual herbicides are applied soil moisture is particularly important and as mentioned last month this more than anything else should decide sowing date, so that the herbicides applied can work to their optimum.

Seedbed management

Good moist seedbeds will also encourage prompt crop emergence which is important for the later sowings as crop competition is an important factor for these.

Those who only have broad leaved weeds to worry about should still aim for autumn treatment as treating when target plants are small will make herbicides more effective.

Slugs have been a problem again, appearing with every rain event and monitoring should continue as cereal crops emerge. Remember to follow stewardship guidelines, particularly if using metaldehyde.

Ferric phosphate products are as effective as metaldehyde and currently of a similar price so should be considered for all applications, but particularly where there is a risk of run-off or other means of water contamination should metaldehyde be used.

Winter bean crops will typically be sown from the middle of this month, or whenever wheat sowing has finished and since weed control centres around pre-emergence treatment, as with cereals soil conditions for optimum performance from these should influence sowing date.

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

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