With magnesium deficiency discolouration begins on the older, lower leaves where it then moves upwards until all foliage is affected. This type of deficiency can be seen as yellowing between the green veins of the leaf. These yellow areas may turn brown. A common and serious disorder which is made worse by standard feeding.
Cultural methods; Spray the affected plants with epsom salts or use a foliar spray containing magnesium.
Product solution: Use a fertilizer which contains magnesium (Mg) - Phostrogen all Purpose Plant Food, Phostrogen Tomato Food, Phostrogen Tomato and Vegetable Food.