Guidelines for insecticides have been updated to minimise the risk of resistance developing when relying on foliar sprays to control pests in cereals that were previously managed by neonicotinoid seed treatments.
This month (17 September) sees the withdrawal of neonicotinoid seed treatments for cereals, as the existing EU ban for flowering crops is being extended to all outdoor crops.
The ban covers three key neonicotinoids: imidacloprid, clothianidin and thiamethoxam.
These seed treatments (such as Cruiser and Deter) are widely used to protect cereal crops from barley yellow dwarf virus, which is transmitted by the bird cherry–oat aphid and the grain aphid. This virus causes an average 8% yield loss in untreated crops.
However, after the ban there will be a greater reliance on pyrethroid sprays to control these pests and this increases the risk of resistance.
To help protect the remaining products on the market, the Insecticide Resistance Action Group (IRAG) has updated its guidelines for the management of insecticide resistance in several key UK crops.
The organisation highlights that several UK pests have already developed resistance to pyrethroid-based insecticides, showing that it is a real risk.
Sue Cowgill, AHDB senior crop protection scientist for pests, said that while most crops will be protected by a seed treatment this season, now is the ideal time to consider next year’s strategy.
“The temptation will be to turn to pyrethroids, but resistance monitoring shows this class of chemistry should be a last resort.”
Although there is currently no evidence of insecticide resistance in bird cherry-oat aphid or rose-grain aphid, the story is different for grain aphids. Moderate levels of resistance to pyrethroids have been detected in laboratory assays.
“In practice, this means sprays may not be effective against this pest unless used at their full label rate.”
Where a pyrethroid spray is deemed necessary, she urges growers to ensure good crop coverage is achieved, as the chemistry only has contact activity.
The guidance also asks people to think carefully about the use of tank mixes, as it can result in suboptimal control of targets and drive the development of resistance.
If an insecticide has been applied correctly and has failed to control the target pest as expected, IRAG says further applications of any insecticide from the affected mode of action should not be made.
The full set of insecticide resistance management guidance can be accessed via the AHDB website.