Despite the cold winter, aphids appear not to have been deterred and populations are building up in the field. Vigilance will be required to monitor aphid populations in cereals and other arable and horticultural crops and growers should be prepared to treat with an effective pyrethroid such as Sumi-Alpha, once thresholds have been reached, says Dr. Stormonth, Technical Manager for Interfarm UK Ltd.
"Although we had a colder than usual winter, which should have reduced the aphid population a bit, we are picking up reports of significant aphid numbers out there. Maybe the significant snow falls may have had an insulating effect on these pests as they over-wintered. But what is obvious now is that with the warmer temperatures returning, growers need to be vigilant and to monitor aphid populations in their crops and be prepared to spray, as and when necessary," says David.
He points out that if and when thresholds are reached, it is advisable to choose a persistent aphicide with as benign an environmental profile as possible. "Esfenvalerate, sold as Sumi-Alpha and Sven, has been shown to give the longest protection against aphids and other insect pests, and provides lower risk to bees and beneficials compared with other pyrethroids. It also has strong repellancy effect on aphids and other pests."
David explains that esfenvalerate works through direct contact with the pest, when ingested by the pest, by preventing feeding and by repelling the pest, with all four methods of activity delivering efficient and effective control. "Although esfenvalerate delivers the lowest gms a.i/ha, it also delivers excellent persistence, up to three times that of cypermethrin, due to its strong binding with leaf wax and its relative stability," he says.
He also reports that esfenvalerate has a lower risk to bees and beneficials than other pyrethoids, important when spraying crops later on, as in cereals. He explains that the Stevenson coefficient, which is a calculation based on the LD50 and use rate of gms a.i/ha in the field, shows that esfenvalerate is of measurable lower risk to bees than cypermethrin, alphacypermethrin, lambda cyhalothrin or deltamethrin. "Tests also show esfenvalerate to be of lower risk on beneficials such as lady birds and lacewings."
David Stormonth reminds growers that the threshold to prevent direct feeding damage on the ear in cereals is when aphid numbers are increasing on 50% of tillers during ear emergence, rising to three-quarters of tillers infested between flowering and grain filling. "If the warm weather continues up to and during this stage, treatment may be needed. Sumi-Alpha is recommended at 200 mls/ha for the control of ear aphids, with the latest stage of application being up to and including late milky ripe stage (GS 77)."
"This year growers are able to use esfenvalerate insecticides on many more fully recommended crops. Sumi-Alpha and Sven have label recommendations for use on winter wheat, spring wheat, winter barley and spring barley for the control of aphids, as well as for the control of aphids in potatoes, for the control of pea and bean and thrips in vining peas, edible podded peas, combining peas and field beans, for the control of caterpillars and midges in cabbage, Chinese cabbage, kale, Brussels Sprouts, cauliflower, broccoli/calabrese, Kohlrabi and for aphid, virus, caterpillars, leaf rollers, whitefly, leaf miners and thrip control in ornamental plant production including outdoor and protected bulbs. They also have label recommendations for the control of bibionid larvae in grassland and managed amenity turf, expanding the crop usage range considerably," reports David.
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
