Red Apple Ice Plant Purple Spots: Fungal or Bacterial?

Diagnosing and Treating Purple Lesions on Aptenia cordifolia

Red apple ice plant (Aptenia cordifolia) developing purple spots that expand and kill tissue is a common issue in coastal San Diego. The progression—purple dots → purple patches → necrosis—suggests a pathogen, but the lack of tan/gray centers rules out classic fungal leaf spots.

Fungal vs. Bacterial Symptoms

• Fungal (e.g., Alternaria, Cercospora): Usually have concentric rings, distinct margins, or sporulation (fuzzy centers).
• Bacterial (e.g., Xanthomonas, Pseudomonas): Water-soaked initially, then uniform purple/brown necrosis, often angular or vein-limited. Spread rapidly in wet conditions.

Recommended Treatment Sequence

1. Copper hydroxide (bactericide/fungicide): Hi-Yield Copper Fungicide or similar. Apply per label every 7–10 days. Organic-approved, broad-spectrum.
2. Cultural: Switch to drip irrigation; avoid overhead watering. Remove and destroy severely affected stems. Thin plants for airflow.
3. If copper fails after 3–4 apps: Consider nutritional disorder (e.g., phosphorus deficiency in cold, wet soil) or viral mosaic. Submit sample to UC Cooperative Extension for lab diagnosis.

Why Daconil (chlorothalonil) Didn’t Work

Chlorothalonil is a protectant fungicide with no bactericidal activity. If the pathogen is bacterial, it’s ineffective. Copper covers both.

Monitor new growth; clean growth indicates control. Rotate to a different FRAC group if repeated copper use is needed long-term.