The term "marginal necrosis" or "tipburn" refers to two types of abiotic problems (physiological or non-parasitic) affecting lettuce grown in soil or above ground. They manifest as necrosis starting at the edges of the leaves of the heart or crown of the lettuce, and their expression seems to be linked to a combination of genetic and environmental factors, more or less related to calcium and in particular its transport within plants.
Source: Marginal necrosis or tip burn – Ephytia
