Advice for typical weed control scenarios in October

1. Tactics for weed control from an October drilling date 

For those drilling wheat in October, the longer you can delay, the better it will be for removing as many weeds as possible with a glyphosate application before drilling, and likely the overall result. 

Persistency of pre-emergence actives is an important characteristic to consider. Earlier in the month, while temperatures are likely to be relatively higher, degradation rates will be quicker, but even later in the month persistency matters as the chances of coming back with a top up herbicide start to diminish. 

It’s one of the reasons why we suggest using Proclus (aclonifen) as part of the pre-emergence mix as it has longer persistency than most other options. Diflufenican also had decent persistency, so the Liberator (flufenacet + diflufenican) + Proclus as a pre-emergence makes a good base.  

Remember Proclus must be applied pre-emergence. Another feature to consider is it seems to retain its activity in dry conditions better than some other actives, which might be useful if the drier weather has continued through September. 

Where grass-weeds are a challenge, adding either Avadex (tri-allate), preferably as granules if you have the machinery or contractor availability, or Defy (prosulfocarb) are decent options to add to Liberator + Proclus.  

2. Tactics for those who drilled in September 

 For those who drilled in September, and have challenging grass-weeds, then top up herbicides will likely be required during October. These will likely be needed as any grass-weeds start to germinate – the earlier the better from an efficacy standpoint. 

What to spray will depend a little on the choice of pre-emergence. If you used Liberator + Proclus or a similar flufenacet-based pre-emergence, cinmethylin is perhaps the best top up. It has shorter persistency but good activity against grass-weeds. It’s also generally a bit safer to the crop when used at peri- or post-emergence.   

Another option, whether you used cinmethylin or flufenacet at pre-emergence, could be a metribuzin-based product, such as Alternator Met or Octavian Met (metribuzin + flufenacet + diflufenican). It provides some contact activity, and helps control a wide range of broadleaf weeds, including groundsel and bur chervil.  

If your following crop is likely to be oilseed rape, especially direct drilled, then be mindful of total DFF rates, especially when using it following Liberator because of DFF persistence.  

Metribuzin-based products are also a good option for those, probably on lighter soils, with annual meadowgrass and broadleaf weeds. These are less critical to spray at pre-emergence and so the metribuzin-products, which can be used at either timing, are a stronger option than Liberator with the extra contact activity and wider broadleaf weed spectrum.  

3. What about winter barley? 

Where winter barley hasn’t been sprayed pre-emergence – possibly because grass-weeds, other than annual meadowgrass, are mostly absent, then the metribuzin-based products also fit well as an early post-emergence, potentially timed with a BYDV spray if appropriate. 

 If the more challenging grassweeds are present, then pre-emergence sprays are required. Cinmethylin isn’t an option in winter barley, so Liberator + Proclus is main choice. Proclus can only be used up to 1.0 L/ha in winter barley compared with 1.4 L/ha in wheat because of crop safety. 

As with many residual herbicide applications on cereals, crop safety means it is critical to drill barley to the correct depth of at least 32mm, achieving a good fine, firm seedbed and if at all possible, avoiding heavy rain events just after drilling.   

4. Check for Phoma in oilseed rape 

There are already some decent-sized oilseed rape crops in the region from very early drilling dates. As it currently stands cabbage stem flea beetle attacks seem to have been more sporadic this season, although that could still change. With some crops still being planted in September there will be a range of crop sizes in October. 

With resistance for Phoma available in many varieties, and dry weather in the region, should dampen risk for the disease, keep monitoring for the disease. Smaller crops are more at risk because infections have a smaller distance for lesions to travel to get into petioles leading to stem cankers. Equally crops with decent sized canopies could encourage more investment.   

Liberator® contains flufenacet and diflufenican. Proclus® contains aclonifen. Avadex® contains tri-allate. Defy® contains prosulfocarb. Alternator Met® contains metribuzin, flufenacet and diflufenican. Octavian Met® contains metribuzin, flufenacet and diflufenican. Liberator, Proclus, Alternator Met and Octavian Met 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 2024.