Has it rained enough recently? Have you given any water? Is there a pest on the leaves? In a pot or the ground? If in a pot. Has it been fed or is it pot bound?

Are they the main leaves or new ones at the ends of the twigs. Sometimes fruit trees get a mildew on them in dry weather, so you could give them a fungal spray but make sure it's a safe one made for fruit and veg. to be eaten.
If it's the main leaves, I would agree with Dorjac when he suggests lack of water. They need gallons of the stuff at this time of year, especially if it's a young tree. Annie