mandarin tree needs help

Question

I need help with my mandarin tree. I have attached pictures of the different problems I’m seeing and would appreciate if someone could help me and tell me what I need to do to take care of it. It’s showing dry/dead branches and sooty deposits on leaves and fruit, and the leaves don’t seem to be vibrant.

I fertilize it twice a year with a citrus fertilizer (Jobe’s Fruit and Citrus 3-5-5), and it’s watered with automated irrigation tubes placed near the roots 2-3 inches below the soil 2 times a week for 5 minutes. I don’t do anything besides this.

Please take a look at the pictures below.
Thanks in advance!
Norm

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Answer 1

The sooty deposit on the leaves is very likely sooty mold, a fungus that grows on honeydew secreted by insects like aphids or scale bugs that attack plants. See this article for tips on controlling it:
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm

Some of the other problems you're seeing, like the curling leaves and non-vibrant leaves, could be caused by the insects that are producing the honeydew. Check the tree carefully for any aphids or scale insects:

http://ipm.ucanr.edu/PMG/r107305011.html
https://www.gardeningknowhow.com/edible/fruits/citrus/curling-citrus-leaves.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/control-plant-scale.htm

I see a brown spot on one of the leaves surrounded by a yellowish area. That, along with the branch that's lost its leaves, can be a sign of Alternaria brown spot, a fungal disease of citrus. See this article for more information:
http://edis.ifas.ufl.edu/ch017