Autumn aphid feeding risks BYDV spread
Numbers of the aphids most responsible for spreading Barley Yellow Dwarf Virus are continuing to increase this season, with mild conditions and the high proportion of early sown crops increasing the risk of disease spreading.
Although populations of the Bird Cherry Aphid and Grain Aphid - which pose the greatest threat of transmitting the virus - have hitherto been relatively low, results of the latest national aphid monitoring surveys revealed a 40% increase in numbers of these two key aphid species caught over recent weeks on comparative sites (to 7 October).
"The risk of BYDV infection appears to be shifting ever later; cereal crops emerging before the second week of October - which could be as high as 60% in the highest risk areas - must now be considered as most susceptible to BYDV infection," warns Syngenta Technical Manager, Iain Hamilton. "The earlier crops are infected, the higher the severity of disease will be and the greater the yield loss."
Where mild conditions continue, there is also the chance for secondary infection. Aphids feeding on infected crops pick up disease and perpetuate its spread across the field and to surrounding crops right through the autumn and early winter, he adds.
"Growers need to weigh up the risk based on the timing of the crop emergence and the historic legacy of BYDV on their farm, allied to the current level of aphid activity," he advises. With a lower risk position for many growers where aphid numbers are down this season, there is the flexibility to reduce Hallmark Zeon application rates down to as low as 25 ml/ha.
"In medium to higher risk situations, where crops were earlier to emerge or aphid populations are continuing to build, rates should be increased to 35 or 45 ml/ha accordingly," reports Mr Hamilton.
He highlights that even at the lower rate, the fast knockdown of Hallmark Zeon can eliminate virus carrying aphids well before the half hour feeding required to transmit the virus; the higher rate gives greater persistence and stronger repellency to deter further aphid migration into the crop.
"For a cost of well under £2 per hectare growers can protect against BYDV yield losses that can exceed 30% in winter wheat and over 50% in barley crops," adds Mr Hamilton. "Trials have consistently shown that, even where an insecticidal seed treatment has been used, an October or November application of Hallmark Zeon will significantly reduce virus infection where expected aphid feeding activity continues into late autumn."
Caption: Cereal growers must be on the lookout for Bird Cherry Aphid populations that will continue feeding on crops and transmitting BYDV well into the autumn in mild conditions.
