DiseaseOther
Magnesium deficiency
Older leaves turn yellow between the veins while the veins stay green, often with reddish or purple tints.
Also known as: Interveinal yellowing of old leaves
Symptoms and identification
Yellowing between the veins starts on older, lower leaves and moves upwards. Leaves may develop reddish-purple patches and drop early. It differs from iron chlorosis, which affects the youngest leaves first.
Causes
Acidic, sandy soils, heavy rainfall, and too much potassium fertilizer, which competes with magnesium.
Organic treatment
Spray leaves with Epsom salt solution (1 teaspoon per litre) every two weeks, or water it into the soil.
Prevention
Use a balanced fertilizer with magnesium and add compost regularly.
Chemical treatment (use with care)
Apply magnesium sulphate at the label rate.