Early Blight
Alternaria solani; Alternaria tomatophila
Target-shaped dark brown lesions on tomato and potato leaves, starting on older foliage and working upwards.
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Identify from a photoBackground
Early blight is a fungal disease of tomatoes, potatoes and related crops. Despite the name, it is not necessarily early in the season. It follows stress and dense foliage rather than time of year. Typical lesions are dark brown with concentric rings, giving a target-spot appearance. On potato tubers, dark sunken lesions can develop during harvest if foliage has been affected.
How to identify
- Dark brown leaf spots 5-15mm across with concentric rings (target pattern)
- Yellow halo often around the lesion
- Lower older leaves affected first
- Heavy infection causes defoliation from the ground up
- Tomato fruit lesions: dark sunken leathery areas, often at the stem end
Life cycle
Spores germinate in free water at 20-30C. Infection to new spore production in 5-10 days. Overwinters on infected crop residue and weedy solanums.
Weather triggers
- Temperature: 18-32°C
- Humidity: >75%
- Rainfall trigger: >5mm
- Warm humid weather with overhead watering is worst. Alternating wet and dry days favour disease.
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 sprays as a protectant (Bordeaux, copper oxychloride)
- Remove and bag affected lower leaves promptly
- Mulch to prevent soil splash
Chemical control
- Mancozeb and chlorothalonil are registered protectants for commercial use; availability for home gardens has become restricted. Check current labels
- Rotate with copper to reduce resistance
Always read product labels. Registrations change.
Prevention
- Stake and prune tomatoes for airflow
- Mulch heavily to prevent soil splash onto lower leaves
- Remove volunteer potatoes and solanaceous weeds
- Rotate tomato and potato beds on a 3-4 year cycle
Companion planting
No reliable companion plant prevents early blight.
Biosecurity
Widespread.
Sources
- NSW DPI, Tomato early blight
- Queensland DAF, Early blight in potato
- Agriculture Victoria, Early blight
Accuracy confidence: high. We update this library as new extension guidance is published.
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