Friday, October 19, 2018

Timings vital to ensure optimum crop establishment

September 12, 2017 by  
Filed under Crops


Crop management will be particularly important this autumn following a challenging harvest, writes Richard Overthrow.

As harvest rolls on – weather permitting, planning for next season’s crops is occupying most growers’ thoughts. Oilseed rape will be top of the list but increasingly growers in this region have to plan for a cabbage stem flea beetle campaign.

Cultural control measures against this pest are increasingly important and these all involve ensuring rapid emergence and early development of the rape, to grow away from beetle pressure as soon as possible. Insecticides are becoming less and less effective and if applied then growers have to prepare for disappointment, though such measures will be more successful if the beetles can be sprayed directly; many have reported success with night spraying as they seem to be more active in the crop after nightfall.

If the rape crop is to follow barley then fields will hopefully be cleared early though this should not lead to very early sowing. Recent experiences suggest earlier sown crops get away from flea beetle better but mid August is early enough to start and the drilling window for the crop extends well into September in this area.

This allows careful seedbed preparation to give every chance for good, prompt establishment of the crop, and will also allow brief stale seedbeds for grass weed control. So although early sowing will help against flea beetle, taking time to ensure, as far as possible, a fine firm seedbed with good levels of moisture can have the same effect.


Starter fertiliser is also essential for oilseed rape, again to help grow away from flea beetle attention as well as early weed emergence. Phosphates can be as effective as nitrogen and combinations of these are now commonly used. They should be applied at or very soon after sowing to ensure they are available from the off.

Flea beetle has also caused a change in approaches to weed control. Where it has been a serious problem pre-emergence herbicides are less commonly used, not just because growers want to see an emerged crop before spending money on it but also because such herbicide timings can slow down emergence and subsequent ‘escape’. Early post-emergence treatment is becoming more popular as a result but will be less effective against early weed flushes.

Pre-emergence herbicides cannot be used on broadcast or autocast crops. Here, weed control will have to wait until post-emergence but the low soil disturbance associated with these cultivation methods usually means early weed pressure is low.

Cereal volunteers

With more intense cultivation early flushes of cereal volunteers will be a problem and it is essential these are taken out with a graminicide as soon as possible, and certainly before they start to tiller. Other grass weed control issues will mainly involve the later post-emergence options, though some contribution can come from earlier treatments.

Slug activity could start at any time after sowing. If pelleting is required, consider ferric phosphate as the first choice but if using metaldehyde remember to follow stewardship guidelines. As above, fine firm seedbeds will help suppress slug activity.

Attention to detail in stubble management, to create good stale seedbeds, is important ahead of cereal crops. Good seedbeds will also help residual pre-emergence herbicides, and these are now an important part of grass weed programmes. Recent autumns have been sufficiently wet to allow good seedbeds and effective pre-emergence performance whilst still allowing timely drilling and we can only hope for a repeat this time.

Where grass weeds are particularly numerous sowing should be delayed anyway, this will also allow more time for seedbed preparation and pre-sowing control.

If there are no grass weed problems it is feasible to sow wheat in early September.  If so you need to spend much of this month planning for this. Variety choice, seed rate, herbicide and aphicide strategies can still be complex with early sowings.

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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