Tomato brown spots on leaves
There are 6 common causes, and they need completely different responses — so working out which one you have matters more than treating quickly.
1 of them can kill the plant. Rule those out first.
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.
The 6 causes, and how to tell them apart
1.Late Blight
Act nowFungal disease
Large irregular blotches that look greasy or water-soaked, grey-green at first and turning brown-black. In humid weather a fine white fuzz appears on the underside at the edge of each lesion. Fruit develops firm, greasy brown patches.
How to know it is this one
Lesions look wet or greasy rather than dry and crisp, even in dry weather.
2.Anthracnose
TreatableFungal disease
On fruit, circular sunken spots that darken and develop concentric rings of tiny black dots, often with a pinkish spore ooze in wet weather. On leaves, irregular brown blotches that frequently follow the veins.
How to know it is this one
Sunken circular lesions on ripe fruit that deepen over days.
3.Bacterial Leaf Spot
TreatableBacterial disease
Small dark spots that look wet or greasy, often with angular edges because they stop at the leaf veins, sometimes surrounded by a yellow halo. In humid weather the spots look water-soaked; in dry weather the centres fall out leaving small holes.
How to know it is this one
Greasy, water-soaked appearance, especially in the morning.
4.Early Blight
TreatableFungal disease
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 know it is this one
Concentric rings inside each brown spot — the bullseye is the giveaway.
5.Septoria Leaf Spot
TreatableFungal disease
Many small round spots, a sixteenth to a quarter of an inch across, with dark brown borders and pale tan or grey centres. Under a hand lens the centres show tiny black pinprick dots. Leaves yellow and drop from the bottom up.
How to know it is this one
Very many small spots rather than a few large ones.
6.Sunscald
Mostly cosmeticGrowing conditions
On fruit, a pale whitish or yellow patch on the shoulder facing the sun, which becomes papery, sunken and sometimes greyish as it dries. On leaves, bleached or brown patches on the most exposed surfaces rather than at the edges.
How to know it is this one
Damage on the side facing the sun, not the blossom end or stem end.
Still not sure?
The diagnostic key adds two more questions — which part is affected and where the trouble started — and those usually settle it.
Run the diagnostic key