Diagnosing and Preventing Onion Soft Rot

Symptoms and Cause

Onions that turn mushy, slimy, and foul-smelling in storage are likely infected with bacterial soft rot (Erwinia carotovora). Bacteria enter through neck tissues as bulbs mature, especially in warm, humid conditions or through mechanical injuries, sunscald, or bruises.

Prevention Strategies

• Soil: Use sterilized soil in raised beds to reduce bacterial load.
• Harvest: Handle gently to avoid bruising. Cure in a single layer with excellent airflow (use fans).
• Storage: Cool (32–40°F), dry (65–70% RH), well-ventilated. Braid tops only after thorough curing.
• Rotation: Rotate alliums 3–4 years; avoid planting after brassicas.

Resistant Varieties

Choose storage-type onions with tight necks and multiple papery skins (e.g., 'Copra', 'Stuttgarter', 'Red Wing').