Lettuce is one of the most widespread crops in the world. However, it requires certain growing conditions that can cause situations prone to generating pests and diseases that can kill crops. There are different types of lettuce diseases that can be recognized with the naked eye to deal with quickly to avoid major disasters.
For this reason, we are going to dedicate this article to telling you what the main lettuce diseases are, how to recognize them and what their treatments are.
This disease is one of the most common in lettuce. We are going to see what characteristics it has, what damage it produces and how to treat it.
It can occur in any vegetative state of lettuce, even during transplantation. Its evolution is always influenced by climatic and cultivation factors: excessive humidity, sudden changes in temperature, too cold soil at the time of planting, insufficient ventilation and wounds or necrosis of plant tissue.
The main sources of disease transmission are conidia and plant debris, which are dispersed by wind, rain splash, plastic and condensation droplets in irrigation water. The favorable conditions for the appearance of the disease are the temperature, the relative humidity and the phenology of the crop.
The optimum range of relative humidity is around 95% and the temperature ranges between 17ºC and 23ºC.
These are the damages caused by this disease:
- It can affect small plants in the seedling stage, causing immediate death or preventing their emergence.
- In young plants, the attack usually begins at the base of the leaves, and once affected, the leaves fall to the ground, favoring the development of parasites that kill the plant after a few days.
- In mature plants, foci begin in necrotic or weakened tissue due to imbalances, physiological injury, or bacterial attack. From there, if the environmental conditions are favourable, it invades new tissue.
- Occasionally, the primary infection is from the soil with Botrytis sclerotiorum accompanied by Sclerotium. In this case, the first attack occurs in the area around the neck of the plant, causing the outer leaves to fall to the ground in such a way that the development of the disease is favored.
- Post-harvest losses also are significant and occur in stored lettuce with latent infection. Under incubation conditions with high relative humidity, healthy lettuce in contact with it can become contaminated.
- The first stage of Sclerotinia infection develops in tissues close to the ground, which is why it is located in the area where the plant collar begins to attack. These can occur in both young and adult plants, although their incidence is greater from the heart due to the special humid microclimate that develops in the soil.
- Affected plants stop growing, turn yellow and wither. They offer no resistance when it comes to pull them off, as they will wet, soften and rot the entire neck and the area of the base of the outer leaves.
To prevent and act against white rot we can do the following:
- Wider planting frames during periods of high risk.
- Transplant on a ridge to improve ventilation.
- Seed varieties that are resistant to different varieties of Bremia lactucae are used.
- Preventive treatment begins from the seedbed until the end of the cycle, in plots prone to diseases.
Other Lettuce Diseases
When identifying this fungal disease, it is necessary to look for small black spots on the lettuce leaves. As usual, thrives in high humidity conditions so precautions are sometimes taken during the rainy season.
It usually appears on the oldest leaves before the rest, and It predominates especially in the central nervous system, petioles and leaves.
Small sunken yellowish spots with red or necrotic edges appear on these leaves. Over time, this reddish ring extends inward, causing necrosis of the entire spot.
Powdery mildew is a well-known fungal disease that affects almost all crops. It usually develops on both the tops and bottoms of the leaves, and the outer leaves are covered with white mycelium and have a powdery appearance.
This fungus can appear in any vegetative state of a lettuce crop. It is usually related to high humidity, so irrigation control is very important. Aeration is also a good technique to prevent the spread of this disease.
The attack usually begins on the lower part of the lettuce, although it can also appear on leaves that show damage, problems or physical diseases.
Septoria produces spots on the underside of the leaves. For this fungus to appear, crops must be in areas with high humidity or rainy seasons. Small irregularly shaped chlorotic spots appear on the leaves. Over time, these spots become necrotic and form chlorotic rings around them, a symptom of disease progression.
The disease causes a soft-looking white rot on lettuce leaves. The infection starts at the base of the plant and spreads over time. This fungus can remain in the soil for up to 5 years, so hygiene techniques such as sun exposure are recommended. It usually develops in conditions of high humidity, temperatures between 25-28ºC, sun and rainso spring is usually more abundant.
Black circular spots with concentric circles appear on the leaves. These necrotic spots first appear on the lower leaves of the plant and spread from there. It can lead to defoliation and premature death.
To prevent it, early maturation should be avoided and excessive humidity of the leaves should be avoided. Acaricides, Mancozeb or Zineb can be used. The applications They must be repeated every 10 or 15 days in order to completely eliminate this disease.
I hope that with this information you can learn more about lettuce diseases and their characteristics.