Monday, August 19, 2019

Monitor crops and treat well this autumn

October 1, 2018 by  
Filed under Crops

Emerging crops need special care as the dry summer continues to impact on growers, writes Richard Overthrow.

Cereal drilling is ongoing and while the dry summer prevented significant soil compaction with harvest equipment – allowing low power seedbed cultivations – there was enough moisture around to allow reasonable seedbeds to be prepared.

Crop establishment should therefore be fairly prompt and even. Where residual herbicides are applied, however, soil moisture is critical and as mentioned last month this more than anything else should determine sowing date, so that the herbicides applied can work to their optimum.

Good moist seedbeds will also encourage prompt crop emergence which is important for the later sowings as crop competition is an important factor even where the grass weeds themselves emerge later.

Those fortunate enough to be only addressing broad leaved weeds should still aim for autumn treatment as treating when target plants are small will make herbicides more effective.

Barley Yellow Dwarf Virus

BYDV control programmes will be ongoing, protection is needed until the end of aphid activity, typically in early November. Deter seed treatments were available for the last time and these can protect the crop for up to six weeks after drilling but if this doesn’t cover the whole risk period then follow-up pyrethroid sprays will be needed.

Slugs have been a problem again and 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 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.

Flea beetle

In oilseed rape, cabbage stem flea beetle was late to arrive but was quite severe when it did so. I have talked at length about the benefits of later sowing to combat this: this year many growers followed this advice but mostly because the later sowing was a re-drill.

Even then many crops were lost altogether and frustratingly it’s a crop that demands a lot of expenditure up front, before we know if the flea beetles will allow it to go any further. This issue will dominate rape growing for the near future at least.

Next comes the larva problem, which may start to be seen this month. 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.

Surviving rape crops should 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 like last autumn treatments 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. Centurion Max is commonly used, but check the manufacturer’s guidelines for use with respect to tank mixing and spray intervals.

Propyzamide and carbetamide are commonly-used post-emergence residual herbicides and relied on more where pre-emergence treatment is avoided in flea beetle campaigns.

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. This approach 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 once 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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