What Causes Yellow Leaves on Mandevilla?
The leaves are very yellow, and most have small black spots on them. The plant was transplanted before the blooming season. I fertilized lightly, sprayed with a soap and water solution, but the problem is worse than ever. Plant is two years old.
Certified GKH Gardening Expert
It sounds like a fungus, likely black spot. Treat the plant with a fungicide and this should clear up the problem.