Bacterial spot

tiny dark spots on the leaves, smaller than a match-head, that look wet and greasy. Hold a spotted leaf up to the light and the spot looks see-through — this greasy, water-soaked look is the giveaway. Each spot is dark brown to black with a yellow ring (halo) around it. Look first on the lower and inner leaves, and in the early morning when there is dew, when the spots stand out most.

the spots join up, whole leaves turn yellow and drop off, and dark streaks appear on the stems and leaf-stalks. On the fruit you get small, raised, rough scabby spots — like tiny warts or scabs that crack open — and this is what makes the fruit unsellable. Bare, leafless plants also let the sun scorch the exposed fruit.

early blight makes bigger brown spots with rings inside them, like a target or bullseye, dry and papery on the older lower leaves — not small, wet and greasy. Septoria spots are small too but have pale grey centres dotted with tiny black specks. Bacterial spot spots stay small, dark, greasy-looking with a yellow halo, and the rough scabs on the fruit are its clearest fingerprint.

check every week from the time the plants are pushing out leaves and setting fruit — the development, fruiting and late-fruit stages — and always within a day or two after rain or overhead watering. Look hardest during warm, muggy spells (around 24-30°C and very humid), because warm wet weather is when it explodes.

the germ rides in on the seed and the young transplants (it is 'seed- and transplant-borne'), so inspect your nursery plants before you plant them out. Throw away any seedling with even one dark greasy spot — never plant a spotted seedling, or you carry the disease straight into a clean field.

walk a big 'W' so you cover all four corners and the middle, not just the row by the path. Make about 10 stops and check 5 plants at each (about 50 plants). At each plant look at the lower and inner leaves, the leaf undersides, the stems and any fruit — go early while the dew is still on, when the greasy spots are easiest to see.

the moment you find even ONE plant with fresh, wet-looking spots during a warm wet spell → start copper protection across the whole field now. Because the disease cannot be cured, there is no 'wait until 20%' like with a pest — the first spots are your signal, and every day you wait it spreads further on the splashing rain.

in dry weather, snap off and carry away the worst spotted leaves and pull the worst plants (drop them in a bag, not on the ground). Then start copper straight away. There is no biological spray or handpicking that cures this disease — keeping the field dry and beginning protection early is the 'act early' step.

copper (the one recommended spray, often mixed with mancozeb) is protective, not curative — it coats healthy leaves and fruit so new spots can't take hold, but it cannot heal spots already there. Start at the first sign and repeat every 7-10 days while the weather stays warm and wet. Safety: cover your skin, eyes, nose and mouth; spray in the cool of morning or evening with the wind behind you; keep it off food, drinking water, children and bees; respect the pre-harvest interval (the wait, printed on the label, between your last spray and picking); and wash yourself and your clothes afterwards. Resistance: don't lean on copper alone — the bacteria can get used to copper — so keep up the clean-seed, rotation and dry-watering habits and rotate or tank-mix as the label allows.

if it spreads despite copper, accept that you cannot cure it — keep the field as dry as you can, stop overhead watering completely, remove the worst plants to protect the rest, and pick the clean fruit early before it scabs. When a field is badly hit late in the season, cut your losses: harvest what you can, then pull and destroy every plant and all the debris, do not save seed from infected plants, and come back next season with a resistant variety, clean seed and a fresh, rotated plot.