Vigilance will be required to monitor aphid populations in many arable and horticultural crops and growers should be prepared to treat with an effective pyrethroid once thresholds have been reached, Interfarm UK Ltd has warned.

According to Dr David Stormonth, technical manager for Interfarm UK Ltd, despite the cold winter, aphids appear not to have been deterred and populations are building up in the field.

Stormonth said: “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."

If and when thresholds are reached, it is advisable to choose a persistent aphicide with as benign an environmental profile as possible, Stormonth said. “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," he continues. "It also has strong repellancy effect on aphids and other pests.”

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 continued.

Esfenvalerate has a lower risk to bees and beneficials than other pyrethoids, important when spraying crops later on, as in cereals and crops in flower. 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.