Management of the lettuce root aphid

Lettuce root aphids overwinter on poplar trees before moving into lettuces and wild hosts in summer, where they can reproduce rapidly. Severe infestations can cause direct damage to the root system, resulting in desiccation and potentially plant death.

• Symptoms are more severe in dry seasons because aphids damage roots and reduce water uptake

Scientific name: Pemphigus bursarius

Winged adults are 2 mm long and have a dark head bearing short antennae. The thorax is dark brown or black and the abdomen is brownish-orange with a slight powdering of wax.

Wingless adults have a yellow head with green-grey antennae that are much shorter than the body. The body is yellowish-white and often covered in large quantities of white-grey wax. There are no siphunculi.

Nov–Feb: The aphid overwinters as an egg on Lombardy and black poplar trees.

Mar–May: Eggs hatch into nymphs. These feed on developing petioles, which enlarge to form galls within which the nymphs live and mature to produce a further generation of aphids.

Jun–Jul: Winged aphids are present over a 4–5 week period in late June or early July. These migrate to lettuce and wild hosts, where they reproduce asexually.

Jun–Aug: The wingless progeny migrate to the roots and produce multiple generations. However, their presence is not often apparent until plants wilt. Large infestations cause desiccation and yellowing.

Aug–Oct: Winged aphids migrate back to host poplar trees.

Non-chemical control

Irrigation can be highly beneficial for crops showing signs of damage.

Lombardy poplars should not be planted (for example, as windbreaks) close to areas of lettuce cultivation.

Natural enemies, including ladybirds and hoverflies, attack the aphids in galls on poplar and on lettuce roots.

There are no tested biological control agents or biopesticides available.

Cultivars of lettuce with almost complete resistance to lettuce root aphid (Avoncrisp and Avondefiance) were developed in the UK, but the material has not been used to develop more modern cultivars.

Monitoring

Thresholds

None established.

Insecticide resistance

None known.