Currant lettuce aphid
Description
Immature aphids are wingless, while adults can be either winged or wingless. Adults are 2 -3 mm in length, with long legs and a spindle shaped body and irregular dark markings on the abdomen. The colour of CLA is dependent on the host plant, varying from yellow – green through to pink – red.
Aphids can breed at high rates due to their ability to reproduce asexually. This process is known as parthenogenesis, where female aphids give birth to live clones without requiring males for reproduction, this generally occurs in spring and summer. To survive cold conditions over winter, females lay eggs on their primary host plants which hatch during spring. Generally, winged adults form as a response to overcrowding or reduced food quality, which allows them to disperse to other host plants. CLA are spread primarily by wind currents. CLA can also be spread on infested produce and seedlings.
CLA primarily pose a threat to the marketability of harvested produce as a contaminant. However, large numbers may stunt young plant growth and cause leaves to become pale and distorted. CLA colonies may be visible, although they prefer to feed hidden under leaves or in the centre of lettuces. Heavy infestations can prevent lettuce hearts forming properly, sometimes causing death. CLA also produce a sticky honeydew substance on the leaves, which often leads to sooty mould developing.
Control
Developing a sound integrated pest management strategy (IPM) is vital to manage an infestation of CLA. It is also important to prevent the development of resistance to CLA, which has occurred in other parts of the world.
Where possible plant resistant varieties to reduce the risk of CLA infestation. Hearting lettuce types, such as iceberg and cos lettuce are more susceptible, as aphids colonise within the heart. Fancy and opening heading lettuce types are less susceptible to damage from CLA. Growers should assess pest pressure prior to planting and consider delaying sowing to reduce the risk heavy infestations. The ability of CLA to hide under leaves can make chemical control difficult, therefore planting on row spacings which maximise coverage is advised.
Crops should be monitored regularly so growers can act quickly and apply insecticides. Monitoring of hearting plants will require close inspection of the inner leaves prior to hearting. Once hearting has occurred a more destructive sampling method may be required. Growers are urged to sample several sites distributed throughout the paddock.
Once threshold levels are reached a foliar insecticide may be required. Foliar sprays are most effective prior to hearting in open lettuce varieties. Movento® is a powerful insecticide which is soft on beneficials and fits well into an IPM system. Movento is registered for the control of CLA in lettuce, chicory, endive and radicchio.
References
Dimsey, R (2006), ‘Managing currant lettuce aphid (CLA) in baby leaf crops’, Vegetable Matters of Facts, Number 39, Department of Primary Industries Victoria, Microsoft Word - mofmanagingLA1.doc (ausvegvic.com.au)
McDougall, S and Creek, A (2011), ‘Current lettuce aphid’, Factsheet, Primary Industries, NSW Government, Currant lettuce aphid (nsw.gov.au)
McDougall, S, Westcott, A, Baker, G and Dal Santo, P (2004), ‘Lettuce Aphid Threat’, Vege Notes, Horticulture Australia, untitled (ausvegvic.com.au)
Plant Health Australia (2013), ‘Current-lettuce aphid’, Fact Sheet, Plant Health Australia, Currant-lettuce-aphid-FS.pdf (planthealthaustralia.com.au)
