For the first time, since I planted it four years ago, my orange tree has given fruit this year. The tree is not very big and was literally covered with clusters of fruit, some of which I now realize should have been thinned out. 95 percent of the fruit fell before ripening, all of it rotten. The few oranges I have been able to harvest are of excellent quality but most of these also have rotten patches. Grateful to know what can I use to prevent this and when?