Increased requirement for a persistent pyrethroid in winter cereals
Interfarm UK Ltd are warning winter barley and winter wheat growers to expect a high risk season for BYDV, linked to the mild weather conditions in the last two years, the warm and wet summer and a mild autumn and winter being predicted. They are advising growers to use a pyrethroid insecticide such as esfenvalerate, Sumi-Alpha, a product they have recently acquired from their majority holding company Sumitomo Chemicals.
"With two mild winters and a wet mild summer just passed researchers have predicted that this will result in crops to be at very high risk of BYDV infection this autumn. The research shows that the higher the rainfall in June and August, the higher the number of bird-cherry aphids there are about in the autumn. Also the milder the autumn and winter the longer aphids will survive and thrive. This plus the recent Met Office prediction for another mild winter means that crops will be at greater risk this year right through the autumn, winter and well into the spring. Even if a seed treatment such as clothanidin is used, growers of early sown winter barley and winter wheat will need a post-emergence pyrethroid insecticide that gives at least 6 weeks protection," says Dr. David Stormonth, Technical Manager for Interfarm UK Ltd.
"Clothianidin has become a popular seed treatment and it gives excellent protection against BYDV for 6 to 8 weeks after drilling. But if the autumn and winter remains mild, which it is predicted to be, aphids will be around into November and December and crops will need that boost of control through the application of the persistent pyrethroid, Sumi-Alpha."
David continues that for those crops which didn’t received an insecticide seed treatment, an application of Sumi-alpha is needed sooner rather than later. ADAS recommend a threshold of 170 day degrees above the aphid development temperature of 3°C from crop emergence, which indicates the start of secondary spread of aphids and BYDV within a crop. "Despite the wet August and early September, much winter barley was drilled in time and wheat wheat will be drilled largely in October. The prolonged harvest will have created a very long green bridge effect when aphids have had the opportunity to move between crops and stubbles. Later sowings will mean that each plant has to do more to justify itself in yield, so that any loss to BYDV is even more critical and hence decisions to treat need to move higher up the agenda," says Dr. Stormonth.
"Sumi-Alpha offers the best persistence of all pyrethroids and it shows strong repellancy activity on aphids. It has flexible dose rates according to the risk levels and hence the persistence required. The 165 mls per hectare rate is used in high risk situations and we would expect 6 weeks protection. High risk situations are early drilled crops, crops grown after grass or grassy stubbles, crops in the South and West, in sheltered fields close to hedges and those in coastal areas. For medium risk BYDV situations, a dose rate of 125 mls/ha, would give around 4 weeks of protection and for low risk BYDV situations 100 ml/ha would give similar persistence to cypermethrin," explains Dr. Stormonth.
"Sumi-Alpha also delivers the lowest active ingredient per hectare, just 25 gms a.i/ha, with many other pyrethroids being applied at 100 gms a.i./ha. The pyrethroid market is well serviced in the UK, but we are pleased to have the product that gives the longest protection against aphids and gives growers top class protection against BYDV in winter barley and wheat.
Sumi-Alpha contains 25 gms ai/litre esfenvalerate formulated as a suspension concentrate and is packed in a 1 litre pack. Recommended on all varieties of winter wheat, winter barley, and spring wheat, it is recommended for the prevention of BYDV by preventing aphid. It can be used at a recommended maximum dose rate of 165 mls/ha with 2 applications per crop. It can be applied up until the 31st March of the year of harvest. Esfenvalerate is available as Sumi-Alpha and Sven.
For further comment and information, please contact Dr. David Stormonth, Technical Manager, Interfarm UK Ltd. on 01354 741414 or 07818 036506 (mobile) or via e-mail david.stormonth@interfarm.co.uk
