Lettuce diseases and pests
The database lists 6 problems recorded on this crop. 2 of them can cost the whole harvest, and 2 survive in soil or debris into next season — those are the ones that decide your rotation. The largest number are active in March.
Pressure through the year
The number of problems listed as active in each month. Pick a month to see what to sow, plant and harvest then.
Start from what you can see
What actually prevents them
Water at the base of the plant in the morning, never over the leaves. Splashing soil onto foliage is the delivery route for every problem listed here, and morning watering lets anything that does land dry before nightfall.
Applies to: Downy Mildew
Mulch the soil surface. A physical barrier between last season's spores and this season's lowest leaves removes the first infection of the year, which is the one that seeds all the others.
Applies to: Downy Mildew
Give the plants their full spacing 25×30 cm and keep the centre of each one open. Air moving through the planting dries the leaves faster, and leaf wetness duration is what turns a spore landing into an infection.
Applies to: Downy Mildew, White Mold (Sclerotinia), Slugs & Snails
Rotate this bed and everything else in the same family on at least a three-year cycle. 2 of the problems below survive in soil or crop debris between seasons, so returning the same crop to the same ground hands them the host they were waiting for.
Applies to: Downy Mildew, White Mold (Sclerotinia)
Clear and remove the spent crop at the end of the season rather than digging it in. Debris left on the surface is where the persistent problems overwinter, and next spring they start from your own bed rather than from somewhere else.
Applies to: Downy Mildew, White Mold (Sclerotinia)
Keep watering and feeding even rather than generous. Several problems on this list are not infections at all: they are the plant reacting to a swing in water, temperature or nutrient supply, and consistency prevents them where no spray can.
Applies to: Bolting (Premature Flowering), Tipburn
Keep affected material out of the compost heap — 2 of these survive a garden heap and come back with the finished compost. Bag it for municipal green waste, which is composted at temperatures a garden heap does not reach.
Applies to: Downy Mildew, White Mold (Sclerotinia)
Every listed problem
Ordered by how much they can cost you.
Fungal diseases(2)
- Downy MildewSevere
Angular yellow patches on the upper leaf bounded by veins, with grey-purple fuzzy growth on the underside. Leaves brown and die from the inside of the plant outward.
- How it spreads
- Rain and irrigation splash
- Compost
- Keep out of the compost
- Conditions
- 10–23°C · humidity ≥85% · wet leaves / rain
- First move
- Treat, then re-check in 5–7 days
Also at risk: Cucumbers, Zucchini, Onions, Beetroot, Spinach, Peas
- White Mold (Sclerotinia)Severe
Water-soaked stem and pod rot covered in dense cottony white mould, later embedded with hard black pellets (sclerotia); sudden wilting of branches above the rot.
- How it spreads
- Soil and crop debris
- Compost
- Keep out of the compost
- Conditions
- 10–24°C · humidity ≥90% · wet leaves / rain
- First move
- Remove affected material now
Also at risk: Beans, Sunflowers
Pests(2)
- AphidsModerate
Clusters of tiny green, black or grey insects on new growth and leaf undersides; curled, distorted leaves; sticky honeydew and black sooty mould; ants tending the colonies.
- How it spreads
- Carried by insects
- Compost
- Safe to compost
- Conditions
- 16–28°C
- First move
- Treat, then re-check in 5–7 days
Also at risk: Peppers, Cabbage, Beans, Spinach, Kale, Broccoli
- Slugs & SnailsModerate
Irregular ragged holes with smooth edges in leaves and fruit, seedlings eaten to the ground overnight, and tell-tale silvery slime trails on soil and foliage.
- How it spreads
- Carried by insects
- Compost
- Safe to compost
- Conditions
- 5–22°C · humidity ≥80% · wet leaves / rain
- First move
- Treat, then re-check in 5–7 days
Also at risk: Peas, Celeriac, Swiss chard, Rhubarb, Strawberries, Parsley
Physiological disorders(2)
- Bolting (Premature Flowering)Moderate
A tall flowering stem shoots up from the centre of the plant. Lettuce and spinach turn bitter and milky, onions and beetroot form a hard woody core, brassicas produce a thin stalk instead of a head, and coriander and rocket run to seed within days.
- How it spreads
- Not contagious
- Compost
- Safe to compost
- Conditions
- ≥25°C · dry air ≤50%
- First move
- Fix the cause, not the leaf
Also at risk: Onions, Beetroot, Radishes, Spinach, Broccoli, Rhubarb
- TipburnMild
Brown, dry, papery scorching along the margins of the youngest inner leaves, while older outer leaves stay perfectly green. In hearting lettuce it is hidden inside the head until it is cut, and secondary rot often follows in the damaged tissue.
- How it spreads
- Not contagious
- Compost
- Safe to compost
- Conditions
- ≥24°C · dry air ≤50%
- First move
- Fix the cause, not the leaf
Why rotation matters here
2 of these overwinter in the soil or in crop debris rather than on the plant. Pulling the sick plant does not remove them: they wait for the same host to come back to the same ground.