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Early Blight: how to recognise and treat it

Disease

Early Blight — Photo: Clemson University - USDA Cooperative Extension Slide Series, CC BY 3.0 us, Wikimedia Commons

Symptoms

Brown to black spots on the lower, older leaves first, with concentric rings like a target and a yellow halo; spotted leaves yellow and fall.
Dark, sunken, elongated spots or cankers on stems, often at or just above the soil line.
Fruit infected around the stem end, with sunken, leathery, dark brown to black spots with rings that can spread over the whole fruit.

Organic treatment

Remove infected lower leaves as soon as they appear, and prune lower leaves and stems that touch the soil.
Spray a copper fungicide on a regular schedule from the first spots or before flowering; follow the label.
Clear and destroy plant debris after harvest.

Chemical treatment

Fungicide with azoxystrobin or difenoconazole when the disease is found and the weather stays wet; do not use azoxystrobin for more than two sprays in a row, as the fungus can become 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

Do not grow tomatoes, potatoes or their relatives in the same place for 2–3 years.
Mulch to stop soil splashing onto leaves, and stake plants to keep them upright; do not reuse old stakes or cages that may carry the fungus.
Water at the base of the plant, or early in the day so the leaves dry before night.
Choose more tolerant cultivars; none is fully resistant.

Plants it affects

Sources

Figures checked against these sources.