Q.dwarf kaffir lime tree growing black leaves
It is spring in Sydney, Australia and I have a dwarf Kaffir lime tree in a pot and it is growing new leaves that are completely black. The remaining tree has perfect glossy leaves. What on earth could this be? I gave the tree a sprinkling of chicken manure pellets and feed it a seaweed solution every once in a while. It was potted with a mixture of citrus potting mix and certified organic potting mix for vegetables. Any suggestions appreciated.

This is Sooty Mold.
Here is a link that will help you.
https://www.gardeningknowhow.com/plant-problems/disease/how-to-get-rid-of-sooty-mold.htm