It sounds like a pest (like mealy bugs) or fungal growth (like mold), but a picture could help us to better determine what it is exactly.
Try to keep your lemon on the slightly dry side of evenly moist. Citrus do best with consistant watering. They do not appreciate being kept too wet nor allowed to dry out.
This article should help: https://www.gardeningknowhow.com/edible/fruits/lime/lime-tree-leaf-drop-why-a-lime-tree-is-losing-leaves.htm
Bought in Nassau Bahamas and is potted. It is losing its leaves and looks less than when purchased. I feed it. What to do?
Give it more light; I'm almost sure that is the beginning of your problems. Get the light, water, and soil right before you worry about "feeding" it. Plants actually make their own food from light, air, and water. Fertilizer is just the frosting on the cake, so to speak. Here's an article that will help you: https://www.gardeningknowhow.com/edible/fruits/lime/potted-lime-trees.htm
How to grow a key lime tree?
All lime trees essentially need the same care. These articles will help you:
https://www.gardeningknowhow.com/edible/fruits/lime/lime-tree-tips-care-of-lime-trees.htm
https://www.gardeningknowhow.com/edible/fruits/lime/mexican-key-lime-tree-info.htm
My tree is about 17 years old. Looks pretty bad. Is this a question of fertilization and sun, or is my tree just too old?
And, by the way, I read that some lemon trees can continue to bear fruit for up to 50 years, so I'm hoping there is still a little life left in yours!
I know that Florida had a bit of a cold snap earlier this year - was your lime tree like this before the cold snap?
Have you seen any evidence of insect pests? This article will assist you:
https://www.gardeningknowhow.com/edible/fruits/lime/problems-lime-trees.htm
I can't exactly tell from the photo, but is only one main branch affected? The rest of the tree except for that one spot looks green unless the photo is deceiving me. If the branch is truly dead, you may want to consider removing it with a pruning saw, cutting as close to the trunk as possible. The best time to prune lime trees is early spring or late summer or anytime prior to blooming.
Have you changed how you care for the tree in terms of fertilization or watering? Double-check the care of your key lime tree by reviewing the information in the following article:
https://www.gardeningknowhow.com/edible/fruits/lime/mexican-key-lime-tree-info.htm
It is a large healthy tree but we haven't had limes in a couple of years.
Here is a link to help you pinpoint the issue.
Most reasons for no blooming or limes can be easily corrected.
We have had our key lime tree about 7 or 8 years. Had its first fruit last year - only a few limes. This year there is a bunch but they smell weird and taste horrible. Tree is about 8 to 9 feet tall - nice looking tree. Has southern sun exposure as well as some east and west. Is not where water stands around it. We've tried picking the fruit when it is little and as they grow - trying various sizes. but they all stink! Inside is dry with big seeds, although the last couple picked have been juicy. But still stinky. Any hints or suggestions? Thank you.
The most often problem with dry and small citrus is caused by lack of water and soil nutrients.
Check the moisture level and watering practices to the links below.
Adding 2 to 3 inches of hardwood mulch will help with moisture.
Also a soil test can be very beneficial. This will tell you what you may need to add to the soil for fruiting success.
https://www.gardeningknowhow.com/edible/fruits/lime/mexican-key-lime-tree-info.htm
https://www.gardeningknowhow.com/edible/fruits/lime/dry-lime-fruit-what-causes-dry-limes.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm