Bacterial Spot
Xanthomonas spp.
Small dark water-soaked leaf spots that expand and merge. Common on tomato, capsicum and brassicas after warm wet weather.
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Identify from a photoBackground
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.
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