Magnesium deficiency symptoms start on older leaves of the plants. Marginal yellowing is followed by the occurence of necrotic spots within the chlorotic areas.
The petioles can show a bluish-purple mottling ('Blue disease").
Magnesium deficiency.
Potassium deficiency also shows chlorosis on the leaves, becoming necrotic later, but the necrosis starts from the leaf tips and does not form spots within the intercostal area of the leaves.
Manganese deficiency shows similar symptoms to Mg deficiency, but the symptoms start on younger leaves and there is no band around the midrib that remains green.
