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Garden pests
Lettuce root aphid
Pemphigus bursarius · Insect
Illustration
Small yellowish-white aphids, dusted with waxy powder, that suck sap from lettuce roots out of sight, so plants wilt in the day and stop growing. Keep lettuce well watered, grow varieties sold as resistant, and don't grow lettuce in the same ground the next year.
How to spot it
- Lettuces that wilt during the day, stop growing and fail to heart; badly hit plants turn yellow and can die.
- Pull one up: clusters of small yellowish-white aphids, about 2–3 mm (⅛ in) long, on the roots, covered in white or greyish waxy powder.
- White, woolly-looking patches on the roots, and brown, dying rootlets.
- Damage from midsummer on; in the UK, numbers on the roots peak in August.
- In spring, pouch-like galls on the leaf stalks of nearby poplar trees, where the aphids breed before moving to lettuce.
Easily confused with
Root mealybugs
White wax on the roots too, but the insects are oval and clearly segmented; lettuce root aphids are short and rounded.
Aphids on the leaves
They cluster on shoot tips and under leaves, not on the roots, and have two 'tailpipes' at the rear, which root aphids lack.
Drought
Dry soil makes lettuce wilt and stall in the same way, so pull up a plant and check the roots before deciding.
Where it's a problem
- Worldwide: Found across the Northern Hemisphere and as far as Australia and New Zealand. It is a pest of lettuce mainly in Europe and North America, worst where lettuce grows near poplar trees, where it spends the winter as eggs.
- United Kingdom: Winged aphids fly from poplars to lettuce over four to five weeks from late June, and numbers on the roots peak in August. In late summer they fly back to the poplars to lay their eggs.
- North America: A serious pest mainly where lettuce is grown near Lombardy poplars.
What to do
- Water lettuce well and steadily, especially in dry spells: plants that keep growing fast can still give a fair crop.
- Grow lettuce varieties sold as resistant or tolerant to root aphid.
- Lift affected plants with as much of their roots as you can, then dig the bed over and let it dry out before replanting.
- Don't grow lettuce in the same spot for a year.
- In the UK, fine insect-proof mesh over lettuce from May to August keeps the winged aphids off.
- Where you have a choice, grow lettuce away from poplar trees.
If you use an insecticide, choose one labelled for lettuce root aphid and follow the label and local rules. Sources say control is hard once the aphids are on the roots, so prevention matters most.
Vegetables it affects
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Sources
- RHS: Root aphids
- University of California IPM: Lettuce root aphid
- Pacific Northwest Insect Management Handbook: Lettuce root aphid
- AHDB Horticulture: Management of the lettuce root aphid
- NSW Department of Primary Industries: Pemphigus bursarius (aphid key)
Facts checked Wednesday 21 October 2026. General guidance only: follow your local council, agency and product label.