IN THE FIELD Richard Overthrow
Dry summer continues to dictate crop management
effective than earlier, and many growers have reported little or no damage with September-sown crops. So patience is often its own reward – although waiting can re- quire a lot of nerve.
The risk of running into cold-
Exceptionally dry weather in the run- up to harvest has implications for autumn establishment, says Richard Overthrow
L
ucky growers may have some moisture in post-har- vest seedbeds. But oilseed rape drilling should be delayed where lack of rain means soils re- main dry because sown seed can become dormant if drilled into parched ground.
While this dormancy is most- ly shorter than for volunteers or shed rape seed, it can still lead to a staggered emergence mak- ing early agronomy timings very diffi cult. But any such forced de- lay in rape sowing could have hid- den benefi ts too. Given few, if any, chemical con- trol options, sowing date is the most effective cultural method for fl ea beetle control, and hence the best control method full stop. Early or late sowing, outside the normal window of activity of the beetle, can lead to the crop avoid- ing serious damage.
Late sowing has been more
er, wetter conditions of autumn would mean insuffi cient plant growth going into winter. But as with winter cereals, delayed sow- ing can be a valuable agronomy tool even if, as mentioned above, it is due to excessively dry seed- beds at normal sowing time.
Safe sowing window Even if adequate rain has fall- en and good seedbeds created, it is still worth considering de- layed sowing where the history of fl ea beetle damage suggests a large threat. Experience suggests that in this region the ‘safe sow- ing window’ for the crop extends to mid September anyway. Other benefi ts will show such
as a longer window for stale seed- beds for grass weed control and avoidance of early aphid activity that might introduce Turnip Yel- lows Virus (TuYV). For many, fl ea beetle has forced a change in approach to weed control. Where it has been a serious problem, pre-emer- gence herbicides are less com- monly 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 be- coming more popular as a result but will be less effective against
early weed fl ushes.
Pre-emergence herbicides cannot be used on broadcast or autocast crops. Here, weed control will have to wait until post-emer- gence but the low soil disturbance associated with these cultivation methods usually means early weed pressure is low.
Competition for moisture With more intense cultivation early fl ushes of cereal volunteers will be a problem and it is essen- tial these are taken out with a graminicide as soon as possible, and certainly before they start to tiller. Their main threat is com- petition for moisture and if this is already limited than effects on crop plants could be severe. Other grass weed control is- sues will mainly involve the later post-emergence options, though some contribution can come from earlier residual treatments. Starter fertiliser is also essen- tial for oilseed rape, again to help grow away from fl ea beetle atten- tion and early weeds. Phosphates can be as effective as nitrogen and combinations of these are now commonly used. They should be applied at or very soon after sow- ing to ensure they are available from the start of crop emergence. Careful stubble management,
to create good stale seedbeds, is important ahead of cereal crops.
“
Delayed sowing can be benefi cial – even when due to lack of moisture
Good seedbeds will also help re- sidual pre-emergence herbicides, and these are now an important part of grass weed programmes.
Herbicide timings Recent autumns have been suf- fi ciently wet to allow good seed- beds and pre-emergence perfor- mance has been good whilst still allowing timely drilling but soil conditions should always dictate herbicide timing and hence crop sowing so, if seedbeds are dry, do try to wait a while.
Where grass weeds are par- ticularly numerous sowing should be delayed anyway, this will also allow more time for seed- bed preparation and pre-sowing control.
If there are no grass weed problems it is feasible to sow wheat in early September, though good seedbeds with adequate moisture are still important. If planning to sow early you need to spend much of this month plan- ning for this. Variety choice, seed rate, herbicide and aphicide strat- egies can still be complex.
› Richard Overthrow is a region- al agronomist with NIAB TAG, the UK’s largest independent agrono- my organisation with several re- search centres in East Anglia. For more details, call 01223 342495.
Timely tips
• Assess seedbed moisture before sowing rape
• Consider stale seedbeds for grass weed control
• Target cereal volunteers with a graminicide
• Apply starter fertiliser at or soon aſt er drilling
• Match herbicide timing to soil conditions
Lack of moisture will infl uence oilseed rape establishment
14 ANGLIA FARMER • AUGUST 2018
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