Early Blight
TreatableFungal disease · spreads to other plants · also called alternaria leaf spot, target spot
Early blight is the single most common tomato disease in home gardens. It overwinters in soil and splashes up onto the lowest leaves in rain or from a hose, which is why it starts at the bottom of the plant and climbs. It rarely kills a tomato outright, but a badly defoliated plant produces less fruit and exposes what fruit it has to sunscald.
What it looks like
Brown spots about the size of a pencil eraser with concentric rings inside them, like a tiny archery target. The tissue around each spot turns yellow, and affected leaves eventually go fully yellow and drop.
How to confirm it
- Concentric rings inside each brown spot — the bullseye is the giveaway.
- Starts on the oldest, lowest leaves and moves steadily upward.
- Yellow halo around each spot, spreading until the whole leaf yellows.
- Dark sunken lesions may appear on the stem end of fruit.
What to do
- 1Remove affected lower leaves and bin them — do not compost.
- 2Mulch thickly around the base. Most infection comes from soil splashing up, and mulch stops it.
- 3Water at the soil, never over the leaves, and water in the morning so foliage dries.
- 4If it is climbing fast, a copper or chlorothalonil fungicide slows it. Applied after infection it protects new growth rather than curing old.
What it gets confused with
One observation settles each of these.
Septoria spots are much smaller and far more numerous, with pale grey centres and tiny black dots — no concentric rings.
Late blight lesions are large, greasy and grey-green with no rings, and spread over days rather than weeks.
Preventing it next time
- Rotate tomatoes and potatoes to a different bed each year — three years is ideal.
- Space plants for airflow and prune the lowest 12 inches of foliage.
- Clear all tomato debris at the end of the season.
Plants affected
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.