I found black spots on some leaves of my plumeria. When I was at Sg. Buluh's nurseries, I asked one of them what's wrong with my plumeria that I got these black spots on the leaves. The explanation given was those are old leaves. I find the answer unconvincing. I hope to see my plumeria blooming with fragrant flowers. I hope it won't die on me.
Can someone help to explain what has gone wrong with my plumeria? What's the diagnosis and treatment? Appreciate your help. Thanks in advance.