Tuesday, 1 October 2013

Don’t forget BYDV control, especially if no seed treatment has been used.

Warmer conditions will increase aphid numbers and so increase Barley Yellow Dwarf Virus (BYDV) risk in cereals. This together with early drilling and the recent reported surge in the numbers of bird-cherry aphid in insect traps will mean that growers will need to plan their aphid control carefully this autumn.  If no seed treatment has been used, an effective foliar applied pyrethroid spray will be needed, says Stewart Woodhead, newly appointed Technical Manager for Interfarm.

He explains that aphids, in particular bird-cherry aphids, are already being trapped by the Rothamsted Insect Survey in many areas and are potentially a major threat as they transmit viruses.  “Aphids are the key vectors of BVDV and the bird-cherry aphid (Rhopalosiphum padi) has become a much more important vector these days. In order to prevent aphids from transmitting BYDV, an insecticide with rapid initial activity, good repellency and long-lasting effects will give the necessary protection. 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 up to 6 weeks protection can be obtained.”

“You may be concerned about insecticide resistance but there are three important points to consider – the first is that there is no evidence of pyrethroid resistance to the bird-cherry aphid and the second point is that, even though high resistance to the grain aphid (Sitobion avena) has been reported, a pyrethroid with excellent persistence and in particular strong repellency can prevent the aphid from feeding and so prevent virus transmission.  The third point is that if you use a high dose rate of esfenvalerate, you will increase its persistency and repellent activity. It makes no sense to reduce dose rates,” he says.

Stewart Woodhead says that for the very limited cost of a BYDV insecticide spray, early drilled cereal crops will benefit from protection against aphids, particularly those that haven’t received a seed treatment.  “You might as well add an effective pyrethroid with quick knockdown and long persistence in with your post-emergence herbicide spray. It adds little to the overall cost but could protect your crop from significant yield loss.”

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 Stewart.

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.