Warm autumn increases BYDV risk
Early drilled crops and the continuing mild weather conditions will mean that this will be a high risk year for Barley Yellow Dwarf Virus (BYDV) in winter barley and winter wheat. ADAS are already reporting aphids being found on volunteers and are advising that crops without a suitable seed treatment should be monitored carefully as the earliest crops are those at highest risk.
Dr. David Stormonth, Technical Manager for Interfarm UK Ltd., explains that there are two distinct approaches to the prevention of BVDV, depending on whether the crop has received a seed treatment or not. "The first approach is for cereals that haven’t had an insecticide seed treatment - in fact this is the majority of winter barley and over half of winter wheat. Autumn-sown crops with no insecticide seed treatment are at risk from aphids causing BYDV infections from emergence onwards and will need an effective pyrethroid with quick knockdown and long persistence, such as Sven, sooner rather than later."
He explains that temperature is the key indicator for spray timing. "ADAS use a system of accumulated temperatures taken from crop emergence onwards when aphids are able to colonise plants, in order to calculate when a foliar treatment is needed. This is calculated by taking the daily mean temperature, subtracting 3 from it and then adding the result to the accumulating total until it reaches the threshold level of 170. Crops emerging in the last week of September this autumn could reach the T-sum of 170 by early October."
"You can also use this system in crops that have had a seed treatment as a way of calculating when the top up foliar-applied pyrethroid spray is needed, but the calculation starts six weeks after sowing, rather than from emergence. This is because an effective seed treatment such as clothianidin is likely to give around 6 weeks protection from the time of drilling against aphids. Note this 6 weeks starts from drilling and not from crop emergence, as some may think."
"To prevent aphids transmitting BYDV, an insecticide with rapid initial activity and long-lasting effects will give the necessary protection. Containing esfenvalerate, Sven offers the best persistence of all pyrethroids as well as having strong repellancy activity on aphids."
"Important for this autumn, Sven has an excellent persistence profile. The high aphid risk, number of early drilled crops and warm temperatures this autumn will require the full rate of 165 ml of Sven per hectare and this will deliver a full 6 weeks protection ensuring effective protection right through the autumn.
He mentions that Sven is fully compatible with many post-emergence herbicides including FMX (flumioxazin) as Digital and SumiMax and is highly rainfast.
Developed by Sumitomo Chemical Company, Sven contains 25 gm ai/litre esfenvalerate formulated as an emulsifiable concentrate and 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 controlling aphids at a maximum dose rate of 165 ml/ha, with a maximum of 2 applications per crop. It can be applied up until the 31st March of the year of harvest. It is also recommended on potatoes, vining peas, edible podded peas, combining peas, field beans, cabbages, Chinese cabbage, kale, Brussels Sprouts, cauliflower, broccoli/calabrese, Kohlrabi, ornamental plants, permanent grassland, rotational grassland and managed amenity turf for the control of aphids, caterpillars, weevils, thrips, midges, leaf rollers, leaf miners, whitefly and bibionid larvae and preventing viruses. Esfenvalerate is available as Sven and Sumi-Alpha.
