Troubleshooting Black Stem Lesions on Greenhouse Peppers

Likely Causes

Black, non-rub-off lesions at leaf-stem junctions and upward on stems suggest a fungal or bacterial stem disease (e.g., Phytophthora, Alternaria, or bacterial canker). Cool, wet, low-light conditions favor these pathogens.

Immediate Actions

1. Remove and destroy severely affected plants.
2. Increase ventilation; reduce humidity below 85%.
3. Water at soil level only; keep foliage dry.
4. Apply copper-based fungicide or Bacillus subtilis (Serenade) per label.

Light Deficiency

Elongated, pale lettuce indicates insufficient light. In Newfoundland winters, supplemental halide/LED grow lights are essential for greenhouse production.

Spacing

35 plants in 4×8 ft is overcrowded. Thin to 18–24 inches between peppers; remove lettuce and corn to improve airflow.