⚠ ModerateIrregular necrotic lesions with surrounding chlorotic halos on forest-floor foliage — consistent with Xanthomonas bacterial infection or Cercospora fungal leaf spot.
Bacterial & Fungal Leaf Spot — Xanthomonas & Cercospora spp.
Commonly affects: Ficus lyrata (Fiddle Leaf Fig), Calathea, Dracaena, Dieffenbachia
Dark brown to black spots with yellow halos appear on leaf surfaces, often water-soaked in early stages. Bacterial spots have irregular margins and a translucent, greasy appearance when held to light. Fungal spots (Cercospora, Alternaria) develop concentric rings with a tan, dry centre. Spots coalesce under humid conditions to form large necrotic patches.
Potential Causes
- 1Overhead watering or misting leaving free water on leaf surfaces for extended periods
- 2Introduction of infected plant material without proper quarantine
- 3High humidity combined with poor air circulation encouraging pathogen dispersal
- 4Physical damage from repotting or handling creating entry points for bacterial infection
- 5Infected potting soil or contaminated tools spreading Pseudomonas or Xanthomonas
Solution Steps
- 1Remove and dispose of all visibly spotted leaves in a sealed bag — do not compost.
- 2Sterilise pruning tools with 70% isopropyl alcohol between cuts to prevent cross-contamination.
- 3Apply a copper-based bactericide/fungicide (copper oxychloride or copper hydroxide) to all remaining foliage according to label rates.
- 4Water at the base of the plant — never overhead — using a spouted can or drip system.
- 5Increase spacing between plants and improve air movement to reduce leaf surface moisture.
- 6For bacterial infections, a preventive spray of dilute neem oil + copper solution every 10 days during high-risk periods is effective.
Prevention Tip
Always quarantine new plants in a separate room for a minimum of 14 days before introducing them to your collection. Inspect undersides of leaves and new growth carefully. This single practice eliminates the majority of disease introductions.
Related Issues to Explore
Powdery Mildew — Erysiphe & Golovinomyces spp.
Powdery mildew and bacterial spot often co-occur in humid, overcrowded conditions — improving airflow resolves the environment for both pathogens.
Read guide
Spider Mite Infestation — Tetranychus urticae
Mite stippling is frequently misidentified as early bacterial spot — look for webbing and confirm the cause before choosing a treatment pathway.
Read guide
Stem & Crown Rot — Botrytis & Fusarium spp.
Untreated leaf spot infections can track down into stem tissue — inspect the base of affected plants for early-stage crown softening.
Read guide
