Foliar sprays can control aphid-borne Barley Yellow Dwarf Virus as well as seed treatment and more cheaply. But correct timing – generally four to nine weeks after drilling – is important, according to Syngenta.
Independent trials last year on winter barley showed that one well timed Hallmark Zeon (lambda-cyhalothrin) cut the level of BYDV by more than half compared to a premium insecticide seed treatment, noted the firm’s Michael Tait.
Two sprays in the TAG work virtually eliminated the disease whereas 80% of the untreated crop was hit.
The best spray timings would vary with each season but should coincide with aphid build up, advised Mr Tait.
“In trials the two-spray strategy gave good coverage across the critical autumn infection period.”
The result was an extra 0.5t/ha (4cwt/acre) over where imidacloprid seed treatment had been used, and a chemical saving of £13.50/ha (£5.50/acre).
Where a single spray six weeks after drilling followed seed treatment, just 3% of plants were affected by BYDV compared to over 20% from the seed treatment alone, he noted.
For high risk crops – those drilled early at low seed rates and on farms with a history of BYDV problems – Mr Tait advised an initial 25ml/ha spray of Hallmark Zeon in early October, followed by a second 25ml/ha when two or three more leaves had emerged.
The alternative, standard advice for medium and low risk situations, was a single 50ml/ha treatment in mid to end of October.
“In some instances the single application will suffice, although growers should be ready to go back in if further aphid activity is detected,” said Mr Tait.