What's causing the white dust on the leaves of my Cox apple tree?
Our Advice
From your description it sounds like apple tree has powdery mildew. Spraying with SB Plant invigourator plus 5 grams of baking powder per litre of spray solution at weekly intervals to control this problem. Powdery mildew is often a sign of water stress in plants, so make sure you keep the plant well watered in dry weather.