Black spot (Diplocarpon rosae) is a common fungal disease affecting rose leaves and stems. It appears as:
- Round black or dark purple spots with fringed edges on upper leaf surfaces
- Yellowing leaves that often fall prematurely
- Sometimes purple-black lesions on young stems
The disease thrives in warm, humid conditions and spreads through water splashing or poor air circulation.
Cultural / Biological Control
Clean up fallen debris and mulch annually.
Remove infected leaves immediately (both on the plant and ground).
Water at the base, not overhead.
Organic Treatment
Organic
Organic fungicide: Neem oil, sulfur, or potassium bicarbonate. Apply early in the season and repeat every 7–14 days during wet weather.
Chemical Control
Chemical fungicide: Fungicides containing chlorothalonil, mancozeb, or myclobutanil. Apply early in the season and repeat every 7–14 days during wet weather.
Prevention Tips
Consistent care and dry foliage are the best defenses. A healthy rose is less likely to succumb to black spot.