Early blight

small dark brown to black spots on the OLDEST, lowest leaves — the tired leaves nearest the ground. They start about the size of a pinhead and grow to the size of a small coin.

as each spot grows it forms rings inside rings, like a tiny target or a tree stump (bull's-eye), and a yellow halo spreads around it. Badly spotted leaves turn fully yellow, then brown and dry, and drop off — and the browning climbs UP the plant leaf by leaf.

look for dark, sunken, leathery patches, often with the same faint rings — on stems, on the shoulder (stem-end) of tomatoes, and on potato tubers as dark dry sunken sores.

late blight makes large, pale-green, water-soaked, greasy-looking blotches (often with white mould underneath in wet weather) and spreads fast in cool wet weather — it does not make neat target rings. Early blight is dry-looking, ringed, and starts low and old. Simple leaf scorch or hunger yellowing has no dark ringed spots at all.

early blight attacks from the plant-building stage right through fruiting and into the end of the season (development, mid- and late-season), so start weekly checks once plants are well grown and begin to set fruit — the danger point the plant is most exposed.

look extra hard after warm days around 24-30 C followed by heavy dew, mist or light rain, and where the leaves stay wet — these wet-then-dry spells are exactly when the fungus jumps.

cross the field in a big "W" so you cover all four corners and the middle, not just the row by the path. Make about 10 stops, and at each stop bend down and check the oldest lower leaves of a plant — turn a few over.

you are looking for the very first target-ring spots on the lower leaves. As soon as you find even 1 spotted leaf — and especially once plants have started setting fruit and the canopy is staying wet — treat it as the moment to start protecting. Do not wait for 10 plants to be covered; early blight only gets harder from here.

the moment you see spotted lower leaves, pick them off and carry them out of the field to burn or bury — do not drop them between the rows. At the end of the season remove and destroy all old plants, debris and volunteer (self-sown) plants, because that is where the fungus overwinters to attack next year.

where pressure is high, use a protectant (contact) fungicide — one that coats and shields the leaf surface (for example chlorothalonil- or mancozeb-type products), rather than only a systemic one (that moves inside the plant). Start at the first lesions and re-cover new growth on the schedule on the label, aiming the spray at the lower, older leaves where it begins.

cover your skin, nose, mouth and eyes, spray in the cool of morning or evening with the wind at your back, and keep the spray off food, drinking water, children and bees. Respect the pre-harvest interval — the number of days the label says you must WAIT between spraying and picking fruit — and wash your body and clothes well afterwards.

rotate between different fungicide groups (do not spray the same product every time), so early blight cannot build up resistance to your one reliable spray.

tighten the spray schedule, strip off and remove the worst lower leaves to slow the climb, and check the fungicide is a protectant coating fresh growth. When most of the canopy is already brown and the fruit is spotting, it is too late to save that crop — cut your losses: harvest whatever sound fruit or tubers you can, clear and destroy every plant and all debris, and rotate to a non-related crop next season so you start clean.