Plenum, a brassica insecticide, has been given full label approval for controlling aphids, and could help control Peach Potato Aphid, Syngenta Crop Management UK has announced.

According the company, aphid monitoring has revealed virtually all Myzus persicae (Peach Potato Aphid) could now be resistant to pyrethroids or carbamate insecticides but Plenum, with no resistance issues, offers effective control.

The company said nearly three-quarters of Myzus persicae caught in the key brassica area around Kirton in Lincolnshire are resistant to carbamate insecticides. A 90 per cent incidence of Kdr resistance - limiting the efficacy of pyrethroid insecticides - has also been recorded this season in trials of a new genetic resistance test under evaluation at Rothamsted Research, it warned.

Syngenta Vegetable Crop Manager, Bruce McKenzie, said growers who suspect incomplete control from any insecticide applications switch to Plenum as soon as possible to avoid colonies of resistant aphids building up and migrating into other crops. He said: “Retailer protocols have zero tolerance for aphid infestation on brassicas. As the key harvesting period approaches, growers now have the chance to achieve total control of Myzus persicae with Plenum.”

Plenum has minimal effects on beneficial hoverflies and parasitic wasps that will help prevent subsequent aphid numbers building up, he added.

He also said clearing out resistant aphid colonies from crops would ensure the best possible results with subsequent Hallmark Zeon, Aphox and Dovetail applications.

For best results, McKenzie said Plenum applications should always be used with a seed oil or methylated seed oil derivative adjuvant, such as Phase II. Defra-funded trials at Warwick HRI showed this combination gave complete control of Mealy Cabbage Aphid, as well as resistant strains of Myzus persicae, when carbamate efficacy was seriously reduced. For really serious mixed infestations of Mealy Cabbage Aphid, he urged growers to use Aphox with Plenum.

He also added that aphids stop feeding very quickly after Plenum application, which minimises crop damage and stops any further virus spread. However, it will take several days for aphids to die, which growers should not confuse with resistance, he said.

The Plenum approval covers application to outdoor cabbage, calabrese, cauliflower and Brussels sprout crops. Two applications per crop are permitted at 0.4 kilos per hectare, with a 14-day harvest interval.