Disease
Black spot
Black spot is a fungal disease, most familiar on roses, that causes dark spots with fringed edges surrounded by yellowing, and it spreads fastest when foliage stays wet.
How to confirm it
- Look for dark, roughly circular spots with feathered edges, often ringed by yellow tissue.
- Check whether affected leaves are dropping earlier than unaffected ones.
- Note whether watering wets the foliage or splashes soil onto lower leaves.
Next Steps
Fixes connected to this cause
Remove and treat black spot
Sanitation matters as much as any spray, since black spot spores overwinter in fallen leaves and reinfect the plant the following season.
Improve airflow
Crowded growth traps humidity and makes some fungal and pest problems harder to manage.
Spray neem oil
Neem oil can help with mild powdery mildew or aphid pressure, but it works best after airflow and spacing are already fixed, not instead of fixing them.