Why does my plant have brown spots on its leaves?
Leaf spots are the largest and most confusing category in the database, because a dozen unrelated pathogens all produce a brown mark. The useful information is not the colour but the shape of the spot, its edge, and which leaves went first.
The one observation that decides it
Look at one spot closely and note where on the plant it started. Concentric rings like a target on the OLDEST lower leaves point to early blight or alternaria. Many small spots with pale grey centres and tiny black dots, also from the bottom up, are septoria. Angular spots stopped by the leaf veins are bacterial or downy mildew. Large, greasy, fast-spreading water-soaked patches with no defined edge are late blight, and that one is measured in days rather than weeks.
Start from the plant in front of you
18 things it could be
Ordered by how much they can cost you — if the first entry fits what you can see, rule it out before considering the milder ones.
Dark, water-soaked greasy patches on leaves that rapidly turn brown; white fuzzy sporulation on leaf undersides in humid mornings; firm brown lesions on stems and fruit. Whole plants can collapse within days.
Conditions: 10–25°C · humidity ≥90% · wet leaves / rainFirst move: Remove affected material nowDark, sunken circular lesions on fruit often oozing pink spore masses when wet; irregular dead blotches on leaves along veins; cankers on stems and twigs.
Conditions: 20–30°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Cucumbers, Beans, Raspberries, Blackberries, Walnut trees
Olive-green to brown velvety blotches on leaves that later turn black; corky, cracked scabby lesions on fruit; early leaf drop in severe cases.
Conditions: 6–26°C · humidity ≥80% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Apple trees, Pear trees, Quince
Small, dark, water-soaked angular spots often with yellow halos that may drop out to leave a shot-hole; scabby raised lesions on fruit; defoliation in severe cases.
Conditions: 22–32°C · humidity ≥80% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Peppers, Walnut trees
Angular yellow patches on the upper leaf bounded by veins, with grey-purple fuzzy growth on the underside. Leaves brown and die from the inside of the plant outward.
Conditions: 10–23°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Cucumbers, Zucchini, Lettuce, Onions, Beetroot, Spinach and 8 more
Brown spots with concentric rings forming a target or bullseye pattern, surrounded by yellow halos, on older lower leaves first. Severe defoliation and dark leathery lesions near the stem end of fruit.
Conditions: 20–32°C · humidity ≥75% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysTan circular leaf spots with dark borders dotted with black specks; berries turn brown then shrivel into hard black mummies that stay on the cluster.
Conditions: 15–27°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Grapes
Many small circular spots with dark borders and pale grey centres, often dotted with tiny black fruiting bodies, starting on the lowest leaves after fruit set.
Conditions: 20–26°C · humidity ≥90% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Tomatoes
Round dark brown to black spots with concentric rings, like a tiny target, often with a yellow halo. Spots enlarge, merge and shred in wind. On cauliflower and broccoli the curd develops sunken black specks that make it unusable.
Conditions: 18–28°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Cabbage, Kale, Cauliflower, Brussels sprouts
Tiny dark brown to black specks with narrow yellow halos on leaves, stems and especially fruit, where they stay small and superficial but downgrade quality.
Conditions: 13–25°C · humidity ≥80% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysRounded black spots with feathery, fringed margins on leaves, surrounded by yellowing; affected leaves drop early, leaving bare canes.
Conditions: 18–27°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Roses
Numerous small circular spots with tan-grey centres and distinct reddish-purple borders; spots merge and leaves brown and die in heavy infections.
Conditions: 20–32°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Carrots, Beetroot, Celeriac, Parsnips, Swiss chard, Parsley
Small round chocolate-brown spots scattered over leaves, stems and pods. In the aggressive phase the spots merge into large black blotches, the stems blacken, flowers drop without setting and plants collapse.
Conditions: 15–22°C · humidity ≥90% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysSeen on: Broad beans
Small water-soaked spots on the leaf underside, each surrounded by a wide, pale yellow-green halo. Pods carry greasy, water-soaked patches that later ooze a cream-coloured bacterial slime. Badly infected young plants are stunted with distorted, yellowed growth.
Conditions: 16–23°C · humidity ≥90% · wet leaves / rainFirst move: Remove affected material nowSeen on: Beans
Small purple-brown spots with a light centre appear on leaves; the dead centres drop out to leave clean round holes. Twigs develop sunken cankers that ooze gum, and fruit carries rough, scabby, raised spots.
Conditions: 8–24°C · humidity ≥85% · wet leaves / rainFirst move: Treat, then re-check in 5–7 daysElongated pale blotches between the leaf veins from June, each containing a tiny caterpillar. Blotches merge until leaves are entirely brown and brittle, and the tree may drop its leaves in August as though autumn had come early.
Conditions: 10–30°CFirst move: Watch it before you actPale winding tunnels or irregular blotches within the leaf, with the surfaces intact above and below. Hold the leaf to the light and the larva is visible as a dark speck at the end of its tunnel.
Conditions: 12–30°CFirst move: Watch it before you actSeen on: Spinach, Swiss chard
Small round spots with deep purple margins and a pale grey or white centre, scattered across the older leaves. Spots may also appear on stalks and on the calyx of the fruit. Badly spotted leaves yellow and die.
Conditions: 15–25°C · humidity ≥85% · wet leaves / rainFirst move: Watch it before you actSeen on: Strawberries