Set up the season with effective weed control

Successful cereal establishment and weed control from residual herbicides sets up the season.

Having clean, healthy crops going into winter gives the best opportunity for high yields come harvest. Bayer’s technical team share their thoughts on how to get crops off to the best start.

Aleks Curcic: Bigger yields or bigger weed bills?

With an early harvest and experience from the previous difficult autumns for establishing crops still fresh in the memory, it’s difficult to expect farmers to sit on their hands for too long this autumn, especially if the weather is good for planting.

Growers are weighing up the risk of not getting a crop in versus the technical challenges earlier drilling can cause.

Going early potentially brings lower seed costs, and better yield potential assuming you can manage the higher risks of BYDV, Septoria and grass weeds effectively.

Some of those risks can be mitigated through variety choice: BYDV-tolerant varieties, higher Septoria resistance and super-competitive varieties could all be considered, although it is unlikely you will find the perfect variety for all three, plus high yield and your chosen end market.

The largest risk is probably from an increase in grass weeds, and drilling in September almost certainly commits you to a higher herbicide spend and at least two applications pre-Christmas.

No matter how good the chemical, it’s not realistic to expect one application in September to last through the autumn.

Persistency, though, is essential. Higher soil temperatures in September and early October break down herbicides more quickly than if used later in the autumn, reducing effectiveness.

Two of the key actives, flufenacet and cinmethylin, work by root uptake and are relatively short-lived in the soil.

Proclus^® is different, it binds tightly to the soil surface and is taken up by the weeds shoots when it grows through the herbicide layer.

It is then translocated to the meristems of the plant, disrupting the photosynthetic pathway, causing bleaching and ultimately plant death. It has good persistence and is less affected by dry soil conditions than other residuals.

Apply with a metribuzin co-form such as Alternator^® Met, Cadou^® Met or Octavian^® Met at the true pre-em. timing against all main grass weed species.

Add other actives into the programme to deal with higher pressure situations of particular weeds. Tri-allate for wild-oats, brome and black grass and prosulfocarb against Italian rye-grass and black grass.

Metribuzin co-forms also pick up a wider range of difficult-to-control broadleaf weeds, such as groundsel, crane’s-bill and bur chervil.

Applying them at GS11-12 when these weeds are at cotyledon to first true leaves gives really good results, especially against bur chervil.

In winter barley, Proclus^® at the lower rate of 1.0 L/ha in combination with Liberator^® will also get you off to a good start.

Alternatively, use a metribuzin co-form with no mix partner depending on the weed spectrum and application timing.

Chris McClymont: Getting the rye-grass strategy right

Of the main grass weed species, Italian rye-grass is probably the most difficult to control with the autumn herbicide programme.

A more protracted germination period mean that delayed drilling and the pre-em. can only do so much. If you have a serious problem, you need to plan for one or perhaps even two further applications during autumn.

Drilling date isn’t the most important thing, but any delay is helpful. What you must do is make sure you achieve at least one stale seedbed before drilling.

Thankfully there has been rain since the start of September for most farms which is essential for getting a good chit of weeds.

For grass weed control the ideal timing for spraying off with Roundup® is within two days of drilling to reduce the chances of further weed germination.

Be aware that for BYDV control we advise a 10-day gap to remove the green bridge.

Even though the plan is for a herbicide sequence to protect the crop through autumn it’s still important to start strong.

Firstly, because we still expect peak rye-grass germination in early October around crop drilling. Secondly, getting a long-lasting herbicide like Proclus^® on is insurance in case you can’t get back as planned for the second application.

A metribuzin co-form like Alternator^® Met, Cadou^® Met or Octavian^® Met plus Proclus^® is a very strong start for Italian rye-grass control.

Aim for a follow up 2-4 weeks later depending on conditions and weed threat. Use different chemistry as the basis for the follow up.

Rachel Banks: Effective application

Selecting the best pre-em. chemistry for the weed situation on farm is only part of the story. It has to be applied correctly so it reaches the target at the right time to control weeds without any risk to the crop.

Start with the seedbed. A fine, moist consolidated seedbed is best for residual herbicide efficacy so that has to be the target if at all possible.

You can still get good results in poorer seedbeds, 2024 saw many examples of that, but you cannot rely on it.

Rolling a seedbed pre-application and additionally planning for a sequenced approach can help with getting the best out of poorer conditions.

Remember that surface acting herbicides like Proclus^® need to form a protective layer across the soil. The more even the seedbed, the less surface area it needs to protect.

The flufenacet and metribuzin in a product like Alternator^® Met is more soil mobile so it moves down to the weed germination zone. Soil moisture and no physical barriers in the soil support efficacy.

Aim to make the first residual application at the true pre-em. timing within 48 hours of drilling because weeds are most vulnerable as they germinate.

In earlier drilled crops, it’s particularly important because weeds emerge more quickly in warmer soils.

In most situations a water volume of 200l/ha is the best option for a pre-em. If you go lower to increase work rates, you run the risk of patchy coverage.

Keep boom height 50cm above the soil and apply at 12km/hour for even spray deposition. Angling nozzles can help improve coverage on rougher seedbeds.

Do bear in mind where soils are cloddy, these clods will break down overwinter and expose patches of unprotected soil, regardless of initial coverage.

Alternator^® Met contains metribuzin, flufenacet and diflufenican. Cadou^® Met contains flufenacet, diflufenican and metribuzin. Liberator^® contains flufenacet and diflufenican. Octavian^® Met contains metribuzin, flufenacet and diflufenican. Proclus^® contains aclonifen. Roundup^® contains glyphosate. Alternator^®, Cadou^®, Octavian^®, Proclus^® and Roundup^® are Registered Trademarks of Bayer. 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 cropscience.bayer.co.uk or call 0808 1969522. © Bayer Crop Science Limited 2025.