Bacterial Spot
Xanthomonas spp.
Small dark water-soaked leaf spots that expand and merge. Common on tomato, capsicum and brassicas after warm wet weather.
Background
Several Xanthomonas species cause bacterial spot on vegetables. On tomato and capsicum, the classic symptoms are small dark water-soaked spots on leaves, later dry and papery, often with a yellow halo. On fruit, raised scabby lesions develop. Bacterial spot is typically seed-borne and splash-spread in warm wet weather.
How to identify
- Small dark water-soaked leaf spots, 2-5mm, often with yellow halo
- Older lesions become tan and papery, sometimes with a shot-hole appearance
- Raised scabby lesions on fruit
- On brassicas: V-shaped yellow lesions starting from leaf margin (bacterial black rot)
Life cycle
Bacteria survive on and in seed, crop residue and volunteer plants. Splash-spread by rain and irrigation. Enters through stomata and wounds.
Weather triggers
- Temperature: 20-32°C
- Humidity: >85%
- Rainfall trigger: >5mm
- Warm wet weather, especially with driving rain, is peak risk.
Peak season (southern hemisphere)
Red = active season · Dark red outlined = this month
Affected vegetables & crops
Click any crop to see current prices and growing info.
Climate zones at risk
Organic & low-impact control
- Copper-based bactericides — regular protectant sprays during wet weather
- Remove and destroy affected leaves and fruit
- Avoid working in the crop when foliage is wet
Chemical control
- Copper is the main option; streptomycin-based bactericides are restricted
Always read product labels — registrations change.
Prevention
- Use certified clean seed or treat seed with hot water
- Rotate solanaceous and brassica beds on a 3-4 year cycle
- Avoid overhead watering
Companion planting
No direct companion effect.
Biosecurity
Certain strains of Xanthomonas campestris have regulatory significance on brassica seed.
Sources
- Queensland DAF — Bacterial spot in vegetables
- NSW DPI — Bacterial spot of tomato and capsicum
Accuracy confidence: high. We update this library as new extension guidance is published.