lemon tree

Question

There are a lot of dead small branches in the tree and small fruit.

Answer 1

Multiple citrus diseases can cause dieback of twigs in a lemon tree along with poor fruit production, including Phytophthora or Anthracnose infection or Bacterial Blast. Please see the following articles for help with diagnosis:

https://www.gardeningknowhow.com/edible/fruits/lemons/common-lemon-tree-diseases.htm
http://ipm.ucanr.edu/PMG/C107/m107bpleaftwigdis.html
http://ipm.ucanr.edu/PMG/C107/m107bpfruitdis.html

Because diseases can vary by the region, it is best to also ask a local extension agent or other expert.