Effective weed control on earlier drilled cereal crops this season will depend on a successful residual programme, say agronomists.
Good chemistry is available – but a clear strategy is vital. With many crops going into the ground sooner rather than later, potential weed levels are higher and herbicides have more work to do, says Mark Hemmant of Agrovista.
“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.”
Spray timings
The first spray should be applied within 48 hours of drilling. This will maximise efficacy, the longer you delay the greater risk of below par control, says Darren Adkins, of Bayer Crop Science UK.
“Don’t push the drill and forget about pre-emergence applications. 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.”
Prompt application is particularly important during mild weather because weeds can start germinating surprisingly soon in warmer soils. 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,” he says. “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.”
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, says Mr Adkins.
“Like everything this season it’s a balancing act with no simple answer. 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. “We saw last autumn that cinmethylin in particular can be hot on crops,” says Mr Adkins.
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.”
High ergot harvest makes seed treatment ‘crucial’
Farmers face an increased ergot risk this season following high levels of the fungal disease in harvested grain crops.
Ergot sclerotia can persist in the soil or on infected seed – prompting reminders that growers should consider ergot control when choosing a seed treatment to help reduce the disease threat.
Factors associated with an increased risk of ergot include wet weather at flowering and high grass weed pressure – especially blackgrass. Both were present during the past season.
Immediate concern
Although the immediate concern is the marketability of cereal crops, growers should also take steps to ensure these difficulties are avoided next harvest, says Tom Wheelhouse, technical specialist for crop protection company UPL.
“Colour sorters are in high demand to remove ergot in grain samples and infected seed lots,” says Mr Wheelhouse. “Even if it is colour sorted out of a seed sample, treatment is strongly advised because particles of ergot will still be present.”
The same sclerotia particles will also be present in infected soils. These fields should ideally be sown with a non-cereal break crop, says Mr Wheelhouse, with particular attention paid to grassweed control.
“Selecting a seed treatment with activity on ergot will also greatly help to reduce the risk. Only two products mention ergot on its label,” says Mr Wheelhouse, adding that Rancona-i-Mix (ipconazole + imazalil) has the most substantial reduction claim.
“The label states that Rancona-i-Mix is effective for the suppression of ergot particles in contaminated seed stocks and the reduction in the spread of spores,” says Mr Wheelhouse.
“In reality, UPL trials indicated this will reduce the incidence of ergot by 40-60%.”
