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Bacterial spot: how to recognise and treat it

Disease

Bacterial spot — Photo: Scot Nelson, CC0, Wikimedia Commons

Symptoms

Small water-soaked spots on older leaves that turn dark brown to black and slightly raised, up to about 7 mm across; larger blotches along leaf edges.
Raised, scabby brown spots on the fruit; other rots can enter through them.
Leaves around the spots turn yellow and drop early, leaving fruit exposed to sunscald.

Organic treatment

Pull up and destroy seedlings with spots — never plant them out.
Spray a copper product approved for organic growing at the first sign and repeat every 10–14 days in warm, wet weather; it only protects healthy tissue and gives partial control. Follow the label.
After harvest remove crop debris, self-sown tomatoes and nightshade or ground-cherry weeds, which carry the bacteria.

Chemical treatment

There is no stronger option for gardens — copper (for example copper hydroxide) is the standard bactericide, and many strains are copper-resistant; follow the label dose and pre-harvest interval.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Prevention

Sow certified pathogen-free or hot-water-treated seed and plant only healthy transplants.
Choose pepper varieties resistant to bacterial spot; resistance works only against the races present locally.
Water at the base; splashing from sprinklers and rain spreads the bacteria.
Keep tomatoes and peppers out of the bed for at least a year, until old debris has rotted.

Plants it affects

Sources

Figures checked against these sources.