Q How do I recognise mineral deficiency?
A The two most likely deficiencies are of iron and magnesium. The symptoms are yellowing leaves, especially between the veins, with the veins remaining green.
These symptoms can look similar to viruses so it is advisable to treat the plants for mineral deficiency first, as this is curable. Iron deficiency shows up in the youngest leaves first, which can turn completely yellow. It is more likely to occur if your soil is alkaline as raspberries prefer a pH of 6.0 to 6.5.
Spray with a foliar feed containing chelated iron. If the symptoms are worse in older leaves, you should suspect magnesium deficiency, which is more likely on light, acid, sandy soil. It can also occur in soils with excess potassium, which can interfere with magnesium uptake. Spray with a solution of magnesium sulphate (Epsom salts) two or three times at two-week intervals; use about 500g in 10 litres of water.