Symptoms are yellowing of the very youngest leaves at the top of the plant, with even the smallest veins remaining green; usually caused by over-watering and/or poor soil aeration. It can be treated by spraying with a proprietary iron foliar feed, but you also need to fix the underlying cause.
Symptoms are yellowing of the older leaves with the main veins staying green. This can be due to a number of causes:
- Low soil magnesium levels (especially if potassium level is high)
- Root problems caused by waterlogging, disease, over-application of soluble fertilizers
- Stress due to heavy fruit load
Removing the underlying cause should alleviate symptoms. Use a liquid feed which contains magnesium as well as potassium. Have your soil analysed and apply magnesium fertilizer before the next crop (if required). If it’s really bad you can spray with 1 litre per 10 sq m of a 2% solution of Epsom’s salts, with a little washing-up liquid as a wetter. Be careful, as this can scorch the leaves if done in sunny conditions.