WHY ARE THE LEAVES TURNING BLACK ON MY CANISTEL TREE
MANY LEAVES ARE BROWN TO BLACK
Certified GKH Gardening Expert
It will be difficult to pin down without a photo, but my best guess is something fungal. There are several options from here. My recommendations are as follows:
About a CUP of DOLOMITIC LIME and a TEASPOON OF WETTABLE SULFUR per inch of tree caliper. So a 4 inch wide trunk would need about 4 handfuls of lime and 4 teaspoons of wettable sulfur scattered about away from the trunk. Feeder roots are further out than anchor roots.
Your other defenses will include spray fungicides. This article will help: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm
This article will help you to craft your own fungicides, should you choose this route: https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm