WHY IS THE SKIN OF MY TANGERINES TURNING BLACK?
Certified GKH Gardening Expert
This would be a BAD fungal/bacterial issue. You can attempt to fix this by applying wettable sulfur to the area around the tree, but sometimes this can be hard to control. This article will give you instruction on how to do this: https://www.gardeningknowhow.com/edible/fruits/citrus/citrus-fruit-brown-rot.htm