A dry period during November helped ease fears of another wet autumn, says Richard Overthrow
It’s not often that this region is one of the wettest in the country but a ridiculous October with typically around 200mm of rain was unseasonal to say the least.
Despite my suggestions last month that most will have given up until spring, a dry window in November allowed some further drilling to be done and many completed their winter cereal programme, even putting in all their bean acreage.
The later sown cereal crops shouldn’t need as much herbicide input as earlier sowings which is just as well given that spraying opportunities are rare at this time of year.
There have been issues with some of the winter bean crops sown where pre-emergence treatment is almost the only option but again for many, good conditions for spraying as well as for drilling was asking a bit too much.
Products like propyzamide and clomazone should not be applied post-emergence; carbetamide is the main option for post-emergence treatments at this time of year.
In cereal crops, we should be wary of any mild spells in December that might kick-start aphid activity – and virus spread. That said, conditions throughout the main flight window were not good.
This means numbers of resident aphids will be low. It’s generally only the September-sown wheat and barley crops that attracted significant numbers and these have mostly been treated.
Conditions last month may also have been unsuitable for the sequence of drilling and pre-emergence spraying immediately after and some later sown cereal crops have not been treated.
Many of the residual products can be applied early post-emergence but some have a latest application date of the end of this month – check this if still hoping to treat.
Remember also that the level of herbicide input need not be high for these later sowings and a complex stack could compromise crop health anyway, reducing its competitive ability.
In NIAB TAG trials we regularly see a negative trade-off between herbicide input and crop strength in this way, leading to more grass weeds from higher herbicide input.
Soil conditions are more or less suitable – temperature-wise if not travel-wise – for propyzamide application to oilseed rape. Even if not, few growers are prepared to wait much beyond the end of November to apply it.
There was one recent season when the appropriate soil temperature didn’t occur until March, so some compromise is often necessary. Applying to warm soils in September and early October will shorten the active’s useful life but even if soils are warm now we should get sufficient persistence from it.
Light leaf spot
Early phoma infections were treated but in many crops these have only appeared recently and these are unlikely to form yield-robbing stem cankers so any late autumn fungicides should target light leaf spot, if this is required.
Crops should also be checked carefully for presence and numbers of cabbage stem flea beetle larvae, not with a view to treating as nothing is effective, but to have an idea of likely damage and hence yield potential and level of justifiable expenditure from this point on.
It goes without saying that fields destined for spring cropping may also be a little wet now so should be left alone.
Winter cultivations, even winter spraying-off, rarely helps and with the equipment available today leaving these operations until just prior to sowing can be just as effective in terms of cleaning up weeds and preparing seedbeds.
› Richard Overthrow is a regional agronomist with NIAB TAG, the UK’s largest independent agronomy organisation with several research centres in East Anglia. For more details, call 01223 342495.