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. These areas tear off, and the leaf curls downwards.
Reasons
Potassium deficiency
Magnesium deficiency also shows chlorotic zones, but these start from the leaf tip and are followed by necrosis near the leaf margins only in cases of severe deficiency. The chloroses are yellowish-white, and the veins remain green.