i planted a apple tree, but the leave keep rotting, what can i do to prevent this??

Hi Harj m and welcome... when you say the leaves are rotting do you mean they are dying back and falling off? If so this is perfectly natural at this time of year especially if it has only been planted for a short while. Just make sure you keep on watering to help the tree establish its root system.

Or do you mean they're covered in a white powdery substance and look curled and shrivelled? Not sure what you mean by "rotting leaves"?