Common Lettuce pests

Aphids are the number one pest, including the green peach aphid, potato aphid, and the currant-lettuce aphid (Nasonovia ribisnigri) that colonizes the heart of the head. They are tiny green, pink, or gray soft-bodied insects that cluster on new growth and undersides of leaves, leaving sticky honeydew and stunting the plant, and some spread viruses. Slugs and snails chew ragged holes and leave slime trails, feeding at night and in damp weather, while cutworms sever young seedlings at the soil line. Cabbage loopers, armyworms, and beet armyworm caterpillars chew large holes in leaves, and leafminers (Liriomyza species) tunnel pale, winding trails inside the foliage. Flea beetles pit young leaves with tiny shot-holes, thrips rasp silvery patches and can carry tomato spotted wilt, and animal pests such as rabbits, deer, groundhogs, and birds can graze whole plants overnight.

Common diseases

Downy mildew (Bremia lactucae) is the classic lettuce disease, showing pale yellow angular blotches on the upper leaf with a fluffy white to gray mold on the underside during cool, humid spells. Lettuce drop (Sclerotinia) causes plants to wilt and collapse with a soft, watery crown rot and cottony white growth, and bottom rot (Rhizoctonia) rots the lower leaves where they touch the soil. Gray mold (Botrytis) produces a fuzzy gray fungus on damaged or aging tissue, and powdery mildew leaves a white dusty coating on leaves. Bacterial leaf spot (Xanthomonas) creates dark, greasy, angular spots that can merge, and viruses such as lettuce mosaic and tomato spotted wilt cause mottling, distortion, stunting, and dead spots or ringspots on the leaves.

Prevention

Rotate lettuce so it does not follow lettuce or other aster-family plants for two to three years, and choose varieties labeled resistant to downy mildew, lettuce mosaic, and big vein where available. Space plants for good airflow rather than crowding, and thin seedlings early so leaves dry quickly after rain or dew. Water at the base with drip or a soaker hose in the morning instead of wetting the foliage, and keep beds free of weeds and old crop debris that harbor pests and disease. Start with clean, certified seed and transplants, avoid working among wet plants, and time plantings for the cool ends of the season since lettuce dislikes heat and stress invites problems.

Organic control

Start with a strong blast of water to knock aphids off, and apply insecticidal soap or neem oil directly to the colonies on leaf undersides, repeating as new generations appear and always reading and following the product label. Float lightweight row covers over young plantings to exclude aphids, leafminers, flea beetles, and egg-laying moths, and hand-pick caterpillars and cutworms in the evening; the microbial Bt (Bacillus thuringiensis) targets caterpillars without harming beneficial insects. Manage slugs and snails with hand-picking at night, shallow beer traps, and iron-phosphate slug baits, and set collars around seedlings to stop cutworms. Encourage lady beetles, lacewings, hoverflies, and parasitic wasps by keeping some flowering plants nearby, and for fungal or bacterial leaf diseases remove affected leaves promptly and use a copper product as a last resort according to its label. Because lettuce is grown for its leaves, favor these least-toxic tools and good sanitation over stronger sprays.

Scouting & monitoring

Scout at least twice a week, checking the undersides of leaves and the center of forming heads for aphids, and inspect for slime trails, chewed holes, and leaf tunnels early in the morning or at dusk. Watch new plantings closely for cutworm damage and missing seedlings in the first two weeks, and step up checks during cool, damp, or foggy stretches when downy mildew and gray mold move fast. Turn over a few lower leaves to catch bottom rot and Sclerotinia before plants collapse, and note any yellow mottling or distorted growth that could signal a virus so infected plants can be pulled. Yellow sticky cards help track aphids, leafminers, and thrips so you can act before populations build.

Tips

Prevention beats rescue with lettuce, so grow it fast and unstressed in cool weather with wide spacing, morning base watering, and resistant varieties. Check the heart of the head every few days, since aphids and rot often start hidden inside where a quick water blast, a picked-off leaf, or an early harvest can save the crop.

General home-garden IPM guidance, focused on prevention and least-toxic control. Always read and follow the product label for any pesticide, including organic products. Page updated Aug 4, 2026.