lemon is ripe but has brown spot on bottom of lemon. Did not touch the ground.
Mature trees probably 15 years old. Watered and fertilized regularly. Lemons are ripening but have a brown spot on the bottom. Lemons have not touched the ground at all. Still on the tree.
Certified GKH Gardening Expert
This sounds like citrus brown spot disease. Unfortunately, this is often caused by overwatering. The soil should be allowed to dry out quite a bit in between waterings. This will help control the disease. It can also occur from infected soil splashing up onto the tree, or fruits.
This article will give you more information: https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-fruit-brown-rot.htm