Why Are My Banana Tree Leaves Turning Black?
From Botswana, Africa Sandy soil Drip irrigation
Certified GKH Gardening Expert
This will, usually, occur from fungal/bacterial infections. This is caused by being overwatered, or remaining too wet for too long without a chance to dry out some in between waterings.
A fungicide will be useful, here. This article will help you with fungicide use: https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm