INSURANCE pyrethroid insecticide ear sprays can do more harm than good, warns ADAS.
"They may have a short-term effect on the aphid population, but will knock out some of the natural enemies, allowing later aphid arrivals to increase unchecked," says entomologist Jon Oakley.
Added to that early populations tend to be on the under-side of leaves and many are missed. Using a pirimicarb product is preferable and cost can be off-set by reducing rates to one-third, he says.
"Recommended dose is generally much higher than the amount required to control a moderate infestation. Using a third of the label dose has obvious financial benefits and also leaves the natural enemies in the crop to mop up any aphids that escape the spray."
HGCA-funded work shows growers can still expect over 75% control from such rates, he adds.
Threshold for application is aphids present on half or more tillers prior to flowering, and two-thirds or more of tillers from flowering to the end of grain-fill. "That can be as late as the end of July if you still have good active green leaf area." *