My 50+ year old orange tree was full of beautiful blossoms in the spring but over the summer the leaves have started turning yellow and falling off and the oranges are only about 2 inches in diameter - and falling off. I've lived in this house for 20 years and the tree always had beautiful delicious fruit. About 2 years ago I had a sprinkler system installed on the terrace above the tree so it is getting more water than it used to. Any advice on this problem?

It is probably getting too much water. Citrus trees need to dry out between watering so that at least the top 2 inches of soil is dry. Redirect your sprinkler so that it does not hit your tree at all. You should not water an established inground tree unless you are in a serious drought.

You probably have some root rot (Phytophythora) and have lost some roots, so you may have to prune the top to balance the tree.

Cdoc