Early blight

Alternaria solani

also called Alternaria blight, target spot

Brown leaf spots ringed like a dartboard or tree stump, starting low on the plant and often haloed in yellow.

Fungus Serious Rain splashAirborne sporesSeed-borne Spreads to neighbors

What you'll see

Dark brown spots with concentric rings, giving a distinct bullseye or target pattern.
A yellow halo often surrounds each spot, and neighboring spots merge as they grow.
Symptoms appear first on the oldest, lowest leaves and move upward.
On potato tubers it causes dark, sunken, leathery patches; on tomato fruit, dark leathery lesions at the stem end.
Stems may show dark elongated cankers with the same ringed markings.

Why it happens

A fungus that overwinters on infected debris, on volunteer plants and in the soil, and can arrive on seed and tubers. Its spores are splashed and blown onto the foliage, where stressed or aging leaves are colonized most easily.

Warm weather with heavy dews, humidity or frequent rain suits it, and it presses hardest on plants weakened by drought, poor feeding or a heavy fruit load.

Treating it

Remove and destroy affected lower leaves promptly to slow the spread up the plant.
Water at the base in the morning and mulch well to keep spores from splashing up.
Keep plants strong with steady moisture and balanced feeding so they resist infection.
Improve airflow by spacing, staking and thinning congested growth.
On a crop under real pressure, an approved fungicide program can hold it in check.

Keeping it away

Rotate tomatoes and potatoes on a three- to four-year cycle and clear all debris.
Use certified disease-free seed and seed potatoes, and remove any volunteer potatoes.
Mulch beneath plants and avoid overhead watering.
Grow resistant varieties where the disease is a recurring problem.
Feed and water consistently to avoid the stress that lets early blight in.

Who gets it

Tomatoes and potatoes above all, with aubergine and other nightshades occasionally affected.