Many farmers are intending to drill cereals earlier this season so effective weed control will depend on a successful residual programme. Good chemistry is available, but it needs a clear strategy to get the best result.

Dose of realism

The starting point is an honest appraisal of the situation according to Agrovista's Mark Hemmant. "We've had two difficult autumns so we know it will be difficult to stop growers sowing early."

Earlier drilling means the potential weed levels in crops are much higher and herbicides have more work to do. "We can still use some cultural controls like drilling low pressure fields first, but we have to accept we're going to spend more on herbicides and use the better products to control weeds."

Timing of the first spray

Apply the first spray within 48 hours of drilling to maximise efficacy, the longer you delay the greater risk of subpar control. "Don't push the drill and forget about the pre-em," says Bayer's Darren Adkins. "Drill, roll if you have to and then spray over two days. If you leave it longer, weeds can start to germinate which reduces the efficacy of any spray.

Mr Adkins says prompt application is particularly important in September drilled crops because weeds can start germinating surprisingly soon in warmer soils.

Choose the best

There a several actives available but Mr Hemmant stresses that this autumn calls for the best available.

"We're big fans of Avadex (tri-allate), for me that's the starting point," says Mr Hemmant. "Then you've got to go to use your strongest grass-weed products. We'll probably go the Proclus (aclonifen) + Liberator (flufenacet + diflufenican) route pre-em and then use Luxinum (cinmethylin) early post-em to get the best control across the programme."

Cover all bases

For high weed pressure fields, the plan is most likely a spray at pre-emergence and a second spray a couple of weeks later to control weed germination throughout October into November. But the risk of bad weather means you cannot depend on the second spray so make sure there is decent longevity in the pre-em.

"Like everything this season it's a balancing act with no simple answer," says Mr Adkins.
"Using actives with longer residual activity at pre-em is a good insurance policy. Aclonifen and DFF are longer-lasting so fit well at this timing."

Be flexible on the timing of the second spray to take advantage of suitable application conditions. Two weeks is a good starting point for planning, but weather could dictate a longer gap.

Crop safety

"Heavy rain around the pre-em timing can wash herbicides down to the crop germination zone and cause crop effects," says Mr Adkins. "We saw last autumn that cinmethylin in particular can be hot on crops."

Winter barley and lighter soils also reduce the margin for error and need good attention to detail to achieve the best result.

"Drill crops to at least 32mm depth, properly covered with no open slots to keep the crop seed well away from high doses of residual herbicides. If there is heavy rain around, then it is safer to use a sequence of herbicides than a big stack. This also means you don't run the risk of really heavy rain washing them all away completely."