I have a beautiful Tangerine tree. It has to be at least ten years old and is about 20 ft. high. I live in Italy and the tree is located on the east side of my house which protects it from the sea wind about a mile away. It gets plenty of sun. I pruned and airated it last year and it is full and seems very healthy. The problem is after it produces what seems to be hundreds of fruit, they get to be about 1" in diameter and the majority of them fall off. Is this normal and if not what can I do. I have never used any fertilizer could this be the problem?