Lettuce Diseases

In gardens, lettuce is a fundamental vegetable, it is the salad par excellence and it is one of the first species you think of when you are about to cultivate. The difference in freshness between a salad harvested in the garden and consumed immediately and a purchased salad is particularly palpable, as with all leafy vegetables, which have a very short shelf life. Therefore, it is important to be able to grow lettuce for as long as possible, usually from late winter to late fall.

Cultivation of lettuce is not difficult to maintain in the garden and offers good results even with a natural approach typical of organic farming, focusing on natural fertilization, rotations, careful irrigation and, above all, a ecological defense against diseases, as well as certain parasites. .

The species ( lactuga sativa ) can, in fact, be affected by certain pathologies which it is very important to prevent. Since it is a species with a short cycle, it often makes no sense to carry out treatments with the classic copper green, but it is more practical, especially in small crops, to eliminate the infected parts in the purpose of stopping the spread of the pathogen. Of course, this is true as long as the first symptoms of the disease are detected quickly.

Contents [Ocultar]

  • How to Prevent Lettuce Diseases

  • The worst lettuce diseases

    • Blight lettuce or bremia lettuce

    • powdery mildew

    • rust

    • Early blight

    • septoria

    • anthracnose

    • Leaf edge necrosis

    • bacterial stains

    • virus


How to Prevent Lettuce Diseases

In general, the following good precautions apply to limit the incidence of all lettuce fungal diseases.

  • Avoid overhead watering , because they wet the plants and expose them to stagnant moisture, which promotes the development of fungal pathogens. A drip irrigation system should be preferred, which is also more environmentally friendly in terms of water saving.
  • In case of culture in the greenhouses as is often the case at the end of winter or in autumn, it is necessary prevent the formation of condensation especially by using the openings to circulate the air.

  • Do not plant lettuce too thickly. Often when transplanting a psychological factor intervenes: when the plants are small it is spontaneous to put them together, because otherwise it seems that the soil is wasted, but it must be taken into account that then they will grow and l space may be insufficient for their optimal development. Plants that are too thick are also more easily prone to diseases and in the case of lettuce, the appropriate distances to respect are 20×30 cm or 25×25 cm.
  • Apply rotations in the orchard are increasingly displacing lettuce crops, but also endives and chicory, their close relatives.
  • After transplanting and also afterwards, it is useful to spray the plants with a diluted macerate of equisetum , which has a preventive effect as it stimulates the natural defense mechanism of the plant. In this case, therefore, wetting the foliage is justified.

  • Propagate only healthy seeds . When you intend to harvest seeds from your own lettuce, you must ensure that the plants from which they are harvested are healthy, as some diseases are transmitted primarily through the seed.
  • Do not exceed with fertilizers , not even those based on natural products. When plants absorb a lot of nitrogen, they are visually beautiful and lush, but also more susceptible to attack by pathogens.

The worst lettuce diseases

Now let’s see what are the main lettuce diseases for which the precautions mentioned above apply.

Lettuce blight or lettuce bremia

It is a disease caused by the fungus Bremia lactucae, which is favored by rainy seasons, poorly drained soils and low to medium temperatures (between 10 and 15°C). The attack of bremia begins on the outermost leaves of the clumps, which are covered with white mealy spots on the lower page, and later these can also spread to the inner leaves. Treatments with copper-based products are advisable in the case of large productions or if the time of harvest is distant, because otherwise it is possible to harvest the lettuce and remove the outer leaves affected by mildew. These are assessments that will be made on a case-by-case basis.


Powdery mildew, known as zucchini disease, also manifests as white mealy spots, but normally this condition occurs in mid-summer and affected plants turn yellow and then wilt. However, powdery mildew tends to affect endives and chicory more easily, rarely lettuce, so it is a rarer pathology than downy mildew.


As in the case of other plant species affected by rust, lettuce can also be attacked by specific fungi of the genus Puccinia, which can be recognized by the classic thick rusty pustules on the foliage.

Early blight

When lettuce is affected by the Alternaria fungus, small spots can be observed on the outer leaves which tend to extend up to about 1 cm in diameter. In severe cases, the leaves turn yellow and dry out completely. The pathogen is favored by humidity and warm, temperate temperatures, up to 30°C.


Septoria is another fungus that can attack lettuce, its optimum temperatures for development are between 18 and 25°C with high ambient humidity, and the disease is recognized by irregular areas of chlorine on the leaves and tissue necrosis, with black dotted elements. The pathogen hibernates in crop residues left in the garden, so it is best to put it in the compost pile where it is most likely to be disinfected.


The pathology first affects the outer leaves of the plume, then also affects the inner leaves and manifests as very small white-yellow circular notches with a brown margin. The notches of the anthracnose become necrotic leaving the leaves with holes. This pathology is particularly favored by dense crops and is easily transmitted by infected seeds.

Leaf edge necrosis

Sometimes the head of lettuce has darkened leaf margins, and these can be the result of water and nutrient imbalances (too much nitrogen and little potassium and magnesium in the soil), or bacteria, which is often at the origin of the case of romaine lettuce. It’s important to remember not to over-fertilize, not even with pelleted manure, which is natural but highly concentrated, so it’s easy to overdo it.

Bacterial maculation

This disease is caused by a bacterium of the genus Xanthomonas and, like most diseases, is favored by persistent humidity and prolonged rains. The symptoms, as the name suggests, are spots, which then become necrotic.


Lettuce can also be affected by viruses such as ‘lettuce mosaic virus’ or ‘lettuce nerve thickening virus’. In the first case, the typical mosaic spots can be observed on the leaves, in the second, the thickening of the leaf vein with the formation of latex bags. Sometimes lettuce can also be affected by other types of viruses.

Plant viruses cannot be eradicated by chemicals, let alone by more environmentally friendly products, so it is essential to defend plants against virus vectors, which are mainly aphids. Aphids are easily controlled by promoting their natural predators such as ladybugs, floaters, lacewings and cicadas in the environment and by treating plants with Marseille soap diluted in water. Plants with virus symptoms should be removed from the garden and the knife with which we cut them should be disinfected before being reused for other vegetables.

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