Weed control advice for if and when crops are drilled in the Midlands

1) Options for weed control, if you have or can drill wheat crops 

 It’s not just when or how drilling was achieved, but also the quality that is determining what you should or shouldn’t try to do with residual herbicides. Unfortunately, many of the drills that do a consistent job of getting seed in the ground have been impossible to use this season. 

A huge amount of what has been drilled is not exactly at a consistent seed depth, which causes more issues on top of wet soils. Many fields have also not been rolled, so when we talk about 32mm of consolidated soils above the seed, if it is not consolidated it’s probably should be nearer 50mm to give the depth protection from residuals you’re expecting.  

Where crops were drilled in September before the deluge and pre-emergence herbicides applied, it’s likely during November it might need a top up residual. The decision whether to do so and what with, will depend on what was applied, how much weed control has it given, and did it damage the crop? 

I could write a list as long as my arm of the various top up options. Off the table are Proclus (aclonifen) because it must be applied pre-emergence and potentially cinmethylin if it has been used already. 

Available options include flufenacet-based products, including those containing metribuzin, which are very effective for a second application, as well as the aforementioned cinmethylin if you went with a flufenacet-based pre-emergence.  

Perhaps the first assessment should be whether the applied treatments have done a good enough job. If they have, you might not feel you need a massive residual top up like cinmethylin and you can use something considerably cheaper.  

But if control has been poor, then you might need to consider the Hail Mary of using mesosulfuron in addition to a metribuzin product to provide extra contact activity, particularly if grassweeds are reaching the two-leaf or beyond stage.  

And then there is perhaps what I should call the agronomist’s option, which is Roundup (glyphosate). It shouldn’t be ruled out, but I suspect most growers will kick you off the farm if you suggest spraying off the one bit of wheat you actually managed to get drilled.   

Pretty much the same list applies to the currently very few fields that have been drilled, didn’t receive a pre-em and now the crop has emerged. The strongest Bayer options would be the metribuzin products, although in the worst black-grass and Italian ryegrass situations I would turn to cinmethylin plus a partner as a post-emergence.  

Many fields though are still to be drilled, although here’s hoping by the time you read this, we will have had a window of opportunity.  

The positive for November drilling is that grassweeds should have emerged before drilling, which gives the opportunity to kill them with glyphosate. Use decent doses – weeds could be tillering if they emerged in September, and pay attention to applications. Don’t try and go too quickly to cover ground – this application is probably the most important one of the autumn.  

That combined with the delayed drilling should mean less to come up with the wheat, and the data suggests perhaps that you don’t need to go quite as mad with the residual herbicide as you might have done if you had drilled in the first week of October as planned.  

The last thing you want to do is put any further stress on a November-drilled crop and slow them down with a massive residual mix, so it could be something as simple as just a Liberator (flufenacet + diflufenican) + Proclus, or Liberator + pendimethalin rather than Liberator + Proclus + partners or cinmethylin + partners in these crops.   Do, however, assess how well you’ve drilled these crops. If it’s not great because of just needing to get crops established to some degree, be very careful about using any residual herbicide. Germination is likely to be lower in these crops anyway, even with higher seed rates, don’t compromise it further with herbicide mixes you might not need.   

2) Monitor for light leaf spot in oilseed rape 

Early established oilseed rape is up to your knees already and hopefully has already been growth regulated in some way where needed a few weeks back.  

There is a little bit of Phoma, generally in these earlier drilled crops where leaves are bigger and so you question whether it will be a problem. Most varieties now have decent resistance ratings for both Phoma and light leaf spot, although there are the odd ones which are a bit weaker which will need keeping an eye on.  

As we start to move into November and especially December, it’s worth looking for light leaf spot. It can be remarkably difficult to identify, particularly before February, so if you see a light green circle or something you’re not sure what it is, turn the leaf over as generally light leaf spot symptoms appear on the underside of the leaf first. 

Alternatively, grab five leaves, put them in a sealed bag in the airing cupboard for 48 hours with a slightly moist towel, and that will accelerate any symptom development.   

If you do see an outbreak of light leaf spot and can travel, it could be worth applying some Proline (prothioconazole) because the last thing the crop will need is light leaf spot moving up the stem to the upper canopy and onto the pods, where it causes significant yield loss. 

3) Cover crop destruction as a Christmas escape? 

Killing off cover crops sometime towards the end of December and early January seems to be the favoured period for making sure it is dead enough not to be a slimy mess over the soil surface when drilling the following crop.  

That could mean spraying them off could provide an escape from the family at Christmas, if you need an excuse. 

With a lot of water to take out of soils before drilling, that could provide a counter-reason for delaying termination, although I doubt any cover crop will be providing much of a water pump in January. 

The big thing to remember is that some of cover crop species are notoriously resilient to low glyphosate doses. Some species in these mixes will need 1440g a.s/ha of glyphosate, while even some of the grasses might need a minimum of 1080g/ha. Keep forward speeds sensible as you need to get the active quite low down into what can be big canopies.   

Liberator® contains flufenacet and diflufenican. Proclus® contains aclonifen. Roundup® contains glyphosate. Proline® contains prothioconazole. Liberator, Proclus, Roundup and Proline 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 www.cropscience.bayer.co.uk or call 0808 1969522. © Bayer CropScience Limited 2024.