Boron Deficiency in Lettuce
Boron deficiency causes a reduction in growth, malformation of the young leaves, and development of dark spots, usually near the leaf tip, which later develop into a marginal necrosis. The leaves are thick and brittle and are frequently cupped. Head development is poor, chlorosis also occurs, and the yellow heads become rotten in the center following the death of the growing point.
Tip burn on younger leaves has been associated with boron deficiency but this symptom is likely to be due to other factors. The early stages of boron deficiency can be confused with tip burn which, unlike boron deficiency, does not lead to lack of “hearting” and death of growing point. Roots on boron-deficient plants are brown, short, and knotted in appearance.