Symptoms
Chlorotic spots develop along the margin and in the interveinal area of older leaves. Later these spots become necrotic and coalesce so that the whole interveinal tissue is affected.
The discoloration starts from the leaf tip and progresses toward the leaf base.
Reasons
Potassium deficiency
Similar leaf symptoms may be caused by manganese or phosphorus deficiency, which also result in chlorosis, followed by necrosis. However, Mn deficiency is visible on younger leaves first.
Magnesium deficiency causes interveinal chlorosis with necrotic zones later, too, but these are spread over the whole leaf area and do not concentrate on the leaf tip or margin.
Salt stress due to overfertilization may also be a reason for marginal scorching.