Mildew: a major threat to lettuce

In general, the most common lettuce disease that growers have to contend with is downy mildew.

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This appears as a whitish-grey fungus under the leaves, and yellowish blotches on the corresponding areas on the upper surfaces.

The disease starts on the lower, older leaves of the plant, as these are more susceptible. In addition, being on or just above the ground, they are in a moist microclimate that is ideal for the development of the disease.

In many cases, older leaves become infected when the plant is close to maturity. This usually causes little damage, and as long as the wrapper leaves are not infected, there is no need to spray.

WHEN DOWNY IS VERY SERVERE, IT CAN BECOME SYSTEMIC

Low air temperature and high humidity favor the development of downy mildew. The pathogen also requires free water on the leaves to enter the tissues of the plant. Heavy dew may be all that is necessary, and the longer it is present, the greater the possibility of infection.