Southern September Agronomy Advice: Autumn Weed Control Starts Now

After a long, hot and dry summer, the rain has finally arrived across the South and South West. Amounts have been variable, but it has been enough to green up stubbles, bring volunteers through and get autumn preparations moving again.

There is more oilseed rape going in this season, which is positive for rotations and for spreading the workload. But as we move into cereal drilling, it is important not to get caught in the rush. The autumn can look open at the start, then quickly turn wet, and that is when decisions made now start to matter.

The first priority is to know which fields need attention. If you have black-grass, Italian ryegrass or brome, those are the fields that cannot wait. A good plan, the right product on farm and a clear order for drilling and spraying will make a big difference when workload starts to build.

Stale seedbeds – start clean before drilling

Stale seedbeds remain one of the most important parts of autumn weed control. The recent rain has created the opportunity for grass weeds and volunteers to emerge before drilling, and that is an opportunity worth taking.

Reducing the weed population before drilling takes pressure away from the residual herbicide programme. It means residual activity is not being used up on weeds that are already established and gives the soil-applied chemistry a better chance of lasting through the main emergence period.

Glyphosate application quality matters here. Small weeds need even coverage and good deposition. Keep forward speed steady, use sufficient water volume and choose a formulation with the surfactant and water-conditioning support needed to help uptake.

It is easy to focus on getting drilling underway, but the fields with the greatest grass-weed pressure should be prioritised for a clean start. “Stale seed bedding is still incredibly important,” and it remains one of the most cost-effective tools available.

Grass weeds – build a robust residual foundation

Across much of Southern and South West England, black-grass, Italian ryegrass and brome remain the grass weeds that drive autumn programme decisions. Ryegrass in particular is becoming harder to manage in some fields, and reduced cultivation systems can make brome more visible and more persistent.

The starting point in difficult fields should be a robust residual programme built around Proclus®. Proclus® contains Aclonifen, a herbicide with a unique mode of action, and is approved for use in winter wheat and winter barley. It provides a useful base in programmes designed to manage black-grass, Italian ryegrass, brome and a range of broadleaf weeds.

The key is diversity. Proclus® should be used alongside other suitable residual actives, rather than asked to carry the programme by itself. This supports a broader approach to resistance management and gives the crop the best chance of staying competitive through autumn and into spring.

A cleaner crop carries less competition for water, nutrients and light. That means the wheat or barley can make better use of the inputs applied later in the season, rather than competing with grass weeds from the start.

Sequencing – top up protection where travel allows

The strongest approach where difficult grass weeds are the target is generally a robust pre-emergence application followed by an early peri-emergence or two-leaf post-emergence top-up. This is particularly relevant in early-drilled fields, where grass weeds have a longer period to emerge.

However, this has to be realistic. Last autumn gave many growers more spraying opportunities than they had seen for years, but it would be a mistake to assume the same will happen again. If the weather turns wet, field access can disappear very quickly.

Where you can travel and the crop is at the right stage, sequencing allows residual protection to be extended and can help maintain control through the autumn into winter. Where you are drilling difficult ground, off-lying blocks or fields that may be hard to revisit, securing a strong pre-emergence treatment is the priority.

The message is not to use the same approach everywhere. Some fields can wait. Others cannot. Successful growers and advisers have a plan, but they can and will adapt that plan when the weather changes.

Metribuzin – added support for grass and broadleaf weeds

In fields where annual meadow-grass and broadleaf weeds are the main targets, or where a wider residual spectrum is needed, metribuzin can add useful diversity to the programme.

Octavian® Met, Alternator® Met and Cadou® Met contain metribuzin, flufenacet and diflufenican. These three-way co-formulations can support residual grass-weed and broadleaf-weed control in winter wheat and winter barley.

They are particularly relevant where ALS-resistant broadleaf weeds are becoming more common. Groundsel and bur chervil are two weeds that deserve attention, as does the continued challenge of resistant broadleaf populations more widely.

An early post-emergence approach can work well where crop conditions and field access allow. It provides a chance to build on the pre-emergence foundation and deal with weeds while they are still small, rather than carrying difficult populations through to spring.

Cinmethylin can also be considered as an additional active ingredient in difficult grass-weed populations, particularly where resistance or reduced sensitivity is suspected. The choice should remain driven by the weed spectrum, crop timing and the overall resistance-management plan.

BYDV – monitor risk before considering treatment

Barley yellow dwarf virus can cause serious losses in the South and South West. Our warmer autumn conditions can support ongoing aphid movement, crop colonisation and multiplication, particularly in early-drilled cereals.

Starcross suction-trap information indicates that around 15–20% of aphids captured carry BYDV. That does not mean every crop needs treatment, but it does underline why infield monitoring is important throughout the autumn and winter.

Use the AHDB suction-trap network alongside crop inspections, drilling date and local conditions to assess risk. Any insecticide treatment must be justified by the relevant threshold and risk assessment, rather than applied automatically.

Where an insecticide application is justified, there may be an opportunity to align it with an early post-emergence herbicide pass. That can be efficient, but only if crop stage, weed spectrum, tank-mix compatibility and all product labels allow it.

Drilling priorities – protect the fields that cannot wait

There is still maize to harvest in parts of the region, grass reseeding to manage and a lot of cereal land to prepare. That creates a real risk of a logjam when drilling, spraying and other autumn work compete for the same people and machinery.

Preparation is always the key. Have the plan ready before the pressure arrives. Know which fields carry the difficult weeds, which blocks are most likely to lose access if rain arrives and which crops need to be drilled and followed with a pre-emergence treatment without delay.

The aim is to avoid drilling every field first and then finding that the sprayer cannot keep up. In high-risk grass-weed fields, drill and spray as a coordinated operation. Where possible, apply the pre-emergence treatment promptly after drilling, while following the product label and checking seed depth and seedbed quality.

Looking ahead – decisions now shape spring pressure

The decisions made this autumn will shape the grass-weed pressure seen next spring. It is far easier to protect a clean crop through autumn than to try to rescue an established weed population once spray windows become tighter.

The ideal outcome is crops drilled, rolled where necessary, and protected with timely residual herbicides. If follow-up applications are possible, use them strategically to maintain control. If they are not, make sure the pre-emergence programme is strong enough for the field in front of you.

“Decisions now make or break the spring weed pressure that we’re facing.” Start clean, prioritise the difficult fields and build the programme around what you can genuinely deliver.

About Matt Siggs

Matt Siggs is Technical Manager South West at Bayer Crop Science. He supports arable growers and advisers across Southern and South West England on practical crop establishment, grass-weed management and resistance-aware autumn herbicide programmes.

His advice is built around planning, field knowledge and realistic application opportunities. He encourages growers to identify the fields that cannot wait, establish crops well and use diverse weed-control strategies that reduce pressure on spring chemistry.

Proclus® contains aclonifen. Alternator® Met contains flufenacet, diflufenican and metribuzin. Cadou® Met contains flufenacet, diflufenican and metribuzin. Octavian® Met contains flufenacet, diflufenican and metribuzin. Roundup® contains glyphosate. Proclus, Alternator, Cadou, Octavian and Roundup are registered trademarks of Bayer. All other brand names used are Trademarks of other manufacturers in which proprietary rights may exist. Use plant protection products safely. Always read the label and product information before use. Pay attention to the risk indications and follow the safety precautions on the label. For further information, including contact details, visit www.cropscience.bayer.co.uk or call 0808 1969522. © Bayer CropScience Limited 2026