Advice about weed control in cereals for growers in the west

1. Weed control for September-drilled wheat 

For those who have drilled winter wheat in September on land where you’re expecting difficult grassweeds, such as black-grass, Italian ryegrass or bromes, and assuming it has been sprayed with a pre-emergence herbicide, then it will likely need a follow up spray during October.   

It doesn’t really matter which herbicide or combination you’ve used at pre-em, it will likely run out of steam as soil temperatures are such that it will have started to degrade.  

If you went with Liberator (flufenacet + diflufenican) + Proclus (aclonifen), cinmethylin-based products are a possible option at early post-emergence. Personally I think cinmethylin fits better in that slot because it should work well and have better crop safety in that slot than as a pre-emergence spray. 

An alternative, if you have already used cinmethylin as a pre-emergence, or as a top up to Liberator + Proclus could be our range of metribuzin-based products. I like these because they have some contact activity and they’re also good generally on broadleaf weeds, which would help prevent the problems with broadleaf weeds in the spring that many farmers have had this year. In particular, I’m thinking of weeds such as mayweed, groundsel, pansies and speedwells.  

While there’s no limit on the amount of diflufenican you can apply and I’d be happy with up to 120g/ha, if you’re likely to direct drill oilseed rape following the wheat. 

This top up application could also coincide with a spray against aphids transmitting barley yellow dwarf virus – but use one of the various tools to help judge risk.  

2. Weed control for October-sown wheat 

For wheat crops drilled at the very end of September and are still pre-emergence I would still aim to apply one, along with crops drilled during October, where those challenging grassweeds are expected.  

My starter for 10 would be Liberator + Proclus because of the broad spectrum of activity and persistence of efficacy. You can then add in other products depending on risk of crop damage and what you are trying to control. The two main additions are prosulfocarb and tri-allate.  

In annual meadowgrass plus broadleaf weed situations, it is a viable strategy to wait until you see the rows before applying any herbicides. In those scenarios, the metribuzin-containing products are a step ahead of the flufenacet / DFF products.  

You can either use the metribuzin products either alone or you can mix them with picolinafen / pendimethalin or chlortoluron-containing products to give a really broad range of weed control. Alone I would keep the rates up, but in mixture you could drop the metribuzin product rate down to 0.5 L/ha. 

3. What about winter barley? 

Again, where winter barley was drilled in September – hopefully not into bad black-grass, Italian ryegrass or brome situations where ideally you wouldn’t be growing the crop – and a pre-emergence has been used because some of those grass-weeds are present, I’d look to follow up with the metribuzin-containing products. It’s about as much contact activity as you can find in the crop.  

Those products, as in wheat, can also be used in the fields with easier annual meadowgrass and broadleaf weeds to control as an early post-emergence option.   

4. Check oilseed rape for Phoma

Various online forecasts for Phoma should help with when oilseed rape crops might reach thresholds for treatment, which is calculated from rainfall from August. 

Consider varietal resistance – most varieties have decent resistance – but remember it is the smaller sized crops that are most at risk of infections moving from leaf lesions into petioles.

With some signs of resistance to azole fungicides found in western Europe, if you do need to spray then Aviator (bixafen + prothioconazole) with its dual modes of action, plus activity against light leaf spot might be worthwhile. 

With some early drilled oilseed rape crops already at a decent size, some growers might be thinking of growth regulation this autumn. I’m not that keen, but the key thing to remember is that any growth regulation will need to be applied early enough before the crop gets too big – it’s not going to shrink the crop, just slow it down.  

Finally there have been some reports of turnip sawfly in oilseed rape this autumn. Damage looks a bit like slug damage, but when you look in the crop you’ll see the caterpillars, so that’s one to keep an eye out for. It can be controlled with a pyrethroid insecticide, if appropriate.   

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