Aphids increase virus risk

HIGH APHID numbers throughout the summer could significantly increase the risk of BYDV (Barley Yellow Dwarf Virus) infection in cereals sown this autumn, growers have been warned.

“Despite changeable weather, cereal aphid populations reached surprisingly high levels in some fields before harvest,” said John Young, technical adviser with BASF.

“At one of our trial sites near Ipswich, numbers peaked at an average of 130 aphids per tiller in early July.

“Lush re-growth of stubbles brought on by wet weather this August will provide a massive green bridge for this high background population of BYDV-carrying aphids to move onto the newly emerging crop.

“Growers should firstly focus on destroying green bridge material well before drilling.”

In the case of cultivation, this should occur two weeks before, but the window could be shortened by using a desiccant herbicide, Mr Young added.

The second step is to guard against airborne aphids, particularly in high risk September drilled crops.

An insecticide such as Sumi-Alpha (esfenvalerate) should be applied as soon as aphids are seen, he recommended.

Green bridge sites could well be an issue this autumn, agreed Jon Oakley from ADAS.

He believed that aphid numbers in the air were “pretty low” at the moment, but much will depend on how warm and damp conditions are this autumn and winter.

Yield losses of up to 2.5t/ha in high risk areas such as south-west England and 1t/ha in East Anglia, were not uncommon following a mild winter, he added.