With some concerns about controlling BYDV because of the risk of aphid resistance, Interfarm UK Ltd is reassuring growers that the use of a strongly repellent, long-lasting pyrethroid at high dose rate is still a good option to use.
“There is no evidence of pyrethroid resistance to the bird-cherry aphid which is one of the major vectors of BYDV and, even though target-site resistance to the grain aphid (Sitobion avena) has been reported in the UK, a pyrethroid with excellent persistence and strong repellency can prevent the aphid from feeding and so prevent virus transmission. If you also use a high dose rate, you will increase its persistency and repellent activity,” says Simon Bishop of Interfarm UK Ltd.
He explains that aphids, in particular bird-cherry aphids, are already being trapped by the Rothamsted Insect Survey in some areas and are potentially a major threat as they transmit viruses. “Aphids are the key vectors of BYDV and the bird-cherry aphid (Rhopalosiphum padi) is a more important vector these days. But BYDV is what is called a persistent virus. This means that the aphid has to feed on the cereal plant for over an hour to transmit it. In order to prevent virus transmission, an insecticide with rapid initial activity, good repellency and long-lasting effects will give the necessary protection as it will prevent the aphid from feeding that long. Sumi-Alpha, which contains esfenvalerate, offers the best persistence of all pyrethroids as well as having strong repellency activity against aphids. It has flexible dose rates according to the persistence required. The full rate of 165 mls per hectare is used in high risk situations where you can get up to 6 weeks protection.”
High risk crops include early drilled crops, crops with a history of BYDV, crops grown after grass or grassy stubbles, crops in the South and West, crops in sheltered fields close to hedges and coastal areas, fields with green bridges of weeds and volunteers and crops that have received no seed treatment, explains Simon.
He advises that in crops treated with clothianidin seed treatment, which will give 6 weeks protection, there is no need to worry for the time being. “But for those crops that have not been treated, they are at risk straight away from the 1 leaf stage of the crop and growers really need to be monitoring crops for aphids. For clothianidin-treated crops a foliar spray of Sumi-Alpha may be required once the seed treatment effectiveness starts to decline. It is worth making the effort as BYDV can cause yield losses of up to 50%.”
Simon explains that temperature is the key indicator for spray timing. “ADAS use a system of T sums – 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, when spraying should take place.”
Developed by Sumitomo Chemical Company, Sumi-Alpha contains 25 gm ai/litre esfenvalerate 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 also available as Sven.
