IRAG Resistance Alert: insecticide-resistant peach-potato aphids on potatoes

So far in 2007, peach-potato aphids (Myzus persicae) have been caught in unprecedented numbers in suction traps and yellow water traps in England. Data collected from suction-trapped aphids and those collected directly from crops indicate that a large proportion have MACE and knock-down resistance (kdr). The MACE forms are resistant to pirimicarb and those with kdr show reduced susceptibility to all of the pyrethroids.

The weather conditions have also favoured aphid development and this, coupled with the high level of resistant forms (MACE and kdr), means that growers must be careful in their selection of insecticidal products. Where M persicae is the dominate aphid species, products based on pirimicarb or a pyrethroid should not be the first choice for aphid control. Products based on alternative chemistry should be selected.

To minimise the risk of problems in controlling M. persicae, the Insecticide Resistance Action Group (IRAG) recommends that growers consider the use of several alternative aphicides* based on active ingredients other than pirimicarb and pyrethroids. These are pymetrozine (Plenum), flonicamid (Teppeki) and two neonicotinoid insecticides, thiacloprid (Biscaya) and acetamiprid (Insyst), none of which are currently compromised by the known forms of resistance carried by M. persicae. Pirimicarb and pyrethroid-based insecticides remain effective against many other aphid species found on potatoes, brassicas and other crops.

Alternating insecticides with different modes of action is a recognised anti-resistance strategy. Insecticides from different chemical groups should be included in the planned programme, along with alternative control (e.g. cultural), and consider their use in IPM programmes. Biscaya and Insyst contain compounds belonging to the same chemical group and should therefore not be alternated.

*All spray programmes should be based on recommended pest thresholds and routine, non-targeted insecticide applications should be avoided. Product label advice should always be adhered to and do not use more applications than absolutely are necessary.