Lettuce downy mildew (Bremia lactucae) – identify and control

Lettuce downy mildew-identify-and-control

Lettuce downy mildew, Bremia lactucae is a disease that has been known since 1843 in lettuce crops in temperate areas of Europe.

Symptoms. This disease occurs on the basal leaves of lettuce, in different phases of growth. It appears as large yellow spots. These spots can enlarge turn yellow and can destroy the whole leaf. If the attack is installed on the first 2 leaves, the seedlings perish. On the leaves of developed plants, the spots enlarge between the veins they can be 3-15 mm in diameter or even more. Near the spots, the underside of the leaf appears a fine, whitish fuzz made up of the mycelium with spores of the fungus.

The pathogen is Bremia lactucae, a pathogen that evolves in optimal conditions. Specifically, if the temperature is maintained between 15-17°C and there is high humidity. In 3-8 hours from the arrival of the spores on the leaves, they give germination filaments (if the temperature is higher than 12°C). The spores move in the water on the leaves and give infections, and after 6-8 days a new generation of spores appears. Their formation is prevented by temperatures higher than 20°C and drought. The transmission of the fungus from plant to plant is done through spores carried by wind and rainwater and irrigation. From one year to the next, the fungus resists through resistance spores that will germinate next spring and will form infection spores again. In addition to lettuce, this pathogen can attack endives and artichokes.

Prevention and control. As preventive measures for lettuce downy mildew, it is recommended to gather and destroy the attacked plants. Lettuce cultivation will be established only in lands well cleaned of plant debris, in a 4-year crop without endives or artichokes, and will not be irrigated by sprinkling.
Chemical treatments are recommended to be applied only to signal the attack, using specific fungicides.

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Lettuce downy mildew (Bremia lactucae) – identify and control
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