In September one of our four indoor hibiscus plants developed yellowing leaves. There were black spots on the back and other disfigurations. It went away when I sprayed with a fungicide.
In late December all four of them have yellowing leaves, but they don't look disfigured. Before I start another spraying regimen, might this just be a seasonal leaf drop?
I have posted several pictures. The first 3 are from December. The last 6 are from early October.
