orange tree

Question

What can cause the leaves to dry up and fall off in the fall of the year while it’s bearing fruit?

Answer 1

If just a few leaves are falling off, it might be normal. If it's many leaves, overwatering, underwatering, sudden temperature changes, and certain diseases can all be responsible. See these articles for more:

https://www.gardeningknowhow.com/edible/fruits/citrus/leaves-falling-off-citrus-tree.htm
http://ipm.ucanr.edu/PMG/C107/m107bpleaftwigdis.html