Lemon tree blooming but fruit turns yellow and falls off. Used epsom salts lightly. Had black fungus on leaves and used aspirin soapy water overnight, then flushed with clear water next morning.
Certified GKH Gardening Expert
Here are some reasons lemon fruit may drop off:
The black fungus on the leaves could be sooty mold. In this case, the key is controlling the insects that produce honeydew which the mold grows on: