My gardenia plant and grapefruit tree have a black growth covering the leaves. What is it?
Black Growth on Leaves
Certified GKH Gardening Expert
Your problem could be attributed to sooty mold, which is often caused by pests. This article will help you learn more:
You can treat this with neem oil. It gets rid of both the fungus and the pests that cause the fungus. Here is more info on neem oil: