Lettuce: Pests & Diseases
Lettuce is one of the most productive crops for succession sowing, from containers to allotment beds. Cool, moist conditions give the best leaves and hearts, while heat and drought encourage bolting. Regular checks are worthwhile because tender foliage attracts slugs, aphids and several diseases that spread rapidly in crowded, damp crops.
Common pests
Slugs and snails are major pests, chewing seedlings, hearts and outer leaves. Aphids, including lettuce root aphid, can weaken plants, curl foliage and leave sticky honeydew. Cutworms and leatherjackets may sever young plants at ground level. Caterpillars, birds and woodlice can also damage leaves, particularly where plants touch damp soil or are covered with decaying debris.
Common diseases
Downy mildew causes angular yellow patches with pale mould beneath leaves, especially in cool, humid weather. Grey mould, or Botrytis, makes soft brown decay and grey fuzzy growth on damaged tissues. Lettuce mosaic virus can cause mottling, distortion and poor growth, often spread by aphids. Damping off affects seedlings, while bacterial soft rot is favoured by wet, crowded conditions.
Prevention
Grow resistant varieties where possible, sow little and often, and give plants generous spacing for airflow. Rotate lettuce away from heavily affected ground and clear old leaves, weeds and crop debris. Water the soil in the morning so foliage dries quickly. Use clean trays and fresh compost for seedlings. Protect new plants with barriers or fleece where slugs, birds or cold conditions are likely to cause damage.
Non-chemical control
Pick slugs and snails after dusk, use physical barriers, and encourage wildlife such as frogs, ground beetles and birds. Biological nematodes can reduce slug numbers when conditions are suitable. Wash small aphid colonies from leaves with water and support hoverflies, lacewings and ladybirds through nearby flowers. Remove diseased plants and heavily infected leaves promptly, keeping them out of the compost heap.
What to look for
Check young lettuce at least twice a week, and daily during wet weather, for slug holes, slime and cut stems. Examine heart leaves and roots for aphids, including white waxy root aphids. After cool, humid spells, inspect leaf undersides for downy mildew. Remove any soft, browning or grey-mouldy tissue before it spreads.
Tips
Keep lettuce growing quickly with regular watering and light shade during hot spells. Harvest outer leaves often, or cut whole heads while firm. Succession sowing every two to three weeks provides fresher crops and reduces the impact of any one pest outbreak.
Lettuce pests & diseases: frequently asked questions
What are the common pests of lettuce?
Slugs and snails are major pests, chewing seedlings, hearts and outer leaves.
What diseases affect lettuce?
Downy mildew causes angular yellow patches with pale mould beneath leaves, especially in cool, humid weather.
How do I prevent pests and diseases on lettuce?
Grow resistant varieties where possible, sow little and often, and give plants generous spacing for airflow.
General guidance for UK home gardens, focused on prevention and non-chemical control. The RHS or a local garden centre can help with tricky cases. Page updated 18 Sep 2026.