What it is
This label covers two related bacterial problems of cabbage that are distinct from black rot. Bacterial leaf spot (Pseudomonas syringae pv. maculicola) causes small dark brown to purplish leaf spots that merge into angular lesions and ragged foliage in cool, wet weather. Bacterial soft rot (Pectobacterium carotovorum, formerly Erwinia) causes water-soaked lesions that quickly turn brown, soft, and mushy - often with a foul smell - mainly in warm, humid conditions and in storage. Both spread by splashing water, tools, and insects.
Symptoms to look for
- Leaf spot: small dark brown to purple leaf spots that merge into angular lesions
- Leaf spot: ragged, torn-looking foliage; severe infection kills leaves
- Soft rot: small water-soaked areas that rapidly enlarge
- Soft rot: tissue becomes soft, brown, and mushy, often collapsing within days
- Soft rot: a strong offensive (foul) odour is usually present, worst in storage
When it spreads
Bacterial leaf spot is favoured by cool, wet weather; soft rot by warm, humid conditions and injured or wet tissue. Both enter through wounds, growth cracks, or natural openings. Splashing rain or irrigation, insects, tools, and handling wet plants spread them; the bacteria survive in soil and plant debris. Soft rot is worst in poorly ventilated storage.
Treatment
Field practices
Use clean, hot-water-treated seed and disease-free transplants, rotate away from brassicas, ensure good drainage and airflow, avoid overhead irrigation and working plants when wet, control insects that wound plants, harvest in dry conditions, avoid bruising heads, and cure and store them cool, dry, and well-ventilated.
Organic options
There is no cure once tissue is infected. Remove and destroy affected plants and heads (do not compost soft-rotted heads). Avoid overhead irrigation and working plants when wet, and handle heads gently to avoid wounds. Copper sprays give partial protection against bacterial leaf spot if started early.
Active ingredients
- copper hydroxide
- copper oxychloride
Chemical options
No chemical reliably cures either disease. Copper bactericides give only partial control of bacterial leaf spot and none of soft rot, which is managed by sanitation and careful handling. Focus on prevention rather than sprays, and rotate copper with other approaches where leaf spot is a problem.
Active ingredients
- copper hydroxide
Safety
This is managed mainly by sanitation and careful handling, not spraying, so chemical exposure is low. If copper is used, wear gloves, a mask, and eye protection and follow the label pre-harvest interval. Do not eat or feed soft-rotted heads to animals, wash hands and disinfect tools after handling infected material, and wash heads before eating.
Preventing it next season
Start with clean, hot-water-treated seed and healthy transplants, rotate crops, keep foliage dry (drip irrigation, spacing, no overhead water), avoid wounding plants and heads, control insects, and store only sound, dry heads in cool, well-ventilated conditions. Careful handling at harvest is the biggest defence against soft rot.