Writing this in mid-August as the UK is about to enter yet another heatwave, and with parched soil conditions prevailing, does feel a little premature, and I really hope that it does not have a similar effect on the weather as did the appointment of Denis Howell as ‘Minister for Drought’ in late August 1976. One of the key take-home messages from this harvest has been the impact of soil structure on the performance of winter crops in particular, with some compacted and poorly structured seedbeds in later sown cereals suffering yield drops of up to 50%. Despite the dry summer and widespread cracking of soils to depth, in many situations there is likely to be a requirement to reset soils with targeted deeper cultivations to enable improved aeration and permeability, but use a spade first to evaluate how deep any compaction is in reality.
Where available, look at yield maps to highlight underperforming areas and help target those areas that may require deeper cultivation, but don’t be tempted to overwork soils and produce too fine a tilth with primary cultivations in case wet weather returns. The fundamentals of good soil structure (and health) have never been more important to optimise crop performance and profitability against a background of declining support and commodity prices.
Hopefully there will be sufficient rain by early September to enable stubbles to green up sufficiently and enable timely spraying-off with glyphosate to control cereal volunteers and grassweeds ahead of the next cereal crop.
A two to three-week interval is required between spraying off cereal stubbles ahead of a subsequent winter cereal to eliminate the risk of direct transfer of barley yellow dwarf virus from any aphids present on volunteer cereals and frit fly damage following oats.
With grassweed insensitivity or resistance to glyphosate developing, minimum rates should be maintained at around 1,000g/ha or above for mixed populations of blackgrass, cereals, brome etc, but for ryegrass nearer 1,500g would be advisable due to confirmed resistance risks. With ryegrass in particular, check for any obviously surviving plants after spraying and consider mechanical removal.
In terms of herbicide strategies for the mainstream cereals, the number one priority for any crop is to ensure an appropriately targeted pre-emergence herbicide is applied, ideally within 48 hours of drilling, otherwise poor grassweed control is more than likely.
Depending on the known grassweed pressures, the key actives that should be considered within a residual programme are Cinmethylin (winter wheat only), Aclonifen, Flufenacet, Triallate and Prosulfocarb; the first two are now regarded as almost essential components of any successful residual ryegrass and blackgrass herbicide programme, but not necessarily together.
Remember that both Aclonifen and Triallate should only be applied pre-emergence of the crop. A new herbicide active, Bixlozone, is also available this autumn and delivers useful additional control of ryegrass, in particular, when included as part of a residual programme – pre-emergence only in winter barley and up to three-leaf stage in winter wheat.
Be wary of overloading pre-emergence stacks, as there is an enhanced risk of significant crop damage where applications are followed by heavy rain within a few days of application, resulting in crop thinning and yield reductions. Splitting out the components and deploying them within both a pre- and a peri-emergence programme will help minimise the risk of significant damage and also extend the residual persistence through November to optimise grassweed control.
By Peter Cowlrick, Technical Director, CCC Ltd.
