What are the black spots on my tomato leaves?
Black or dark-brown spots on tomato leaves are usually early blight or Septoria leaf spot — two common fungal diseases with different spot patterns that are managed the same way.
Early blight (Alternaria solani) produces dark spots with distinctive concentric rings, like a target board, usually surrounded by a yellow halo. Spots are typically larger — 1/4 to 1/2 inch across — and appear on the oldest, lowest leaves first. The surrounding leaf tissue yellows and the leaf eventually dies and drops. In humid summers, it can work its way up a plant by late July.
Septoria leaf spot (Septoria lycopersici) produces smaller, more numerous spots — 1/8 to 1/4 inch, with dark borders and pale gray or tan centers. Under magnification you can sometimes see tiny dark dots in the center (the fungal pycnidia). Septoria also starts on lower leaves and moves up, and also causes yellowing and leaf drop. Both diseases spread through splash from soil, which is why mulch is the single most effective prevention.
Management for both is similar: remove affected leaves as soon as you spot them (bag them, don't compost), maintain a 2–3 inch mulch layer to prevent soil splash, water at the base, and prune lower leaves to keep foliage off the ground. Copper fungicide can slow spread when applied early, before disease is severe — once more than a third of leaves are affected, sprays have diminishing effect.
Neither disease typically kills a plant outright, but heavy infection reduces photosynthesis and can reduce fruit set and size. The goal is slowing the spread, not eliminating it — some presence of both diseases is normal in most gardens by August.
- AnthracnoseSunken, dark circular lesions on ripening fruit, sometimes with salmon-colored spores in the center.
- Black RotV-shaped yellow lesions at brassica leaf margins with blackened veins inside — a bacterial disease that moves through the vascular system.
- Blossom End RotDark, sunken, leathery patch on the blossom end of tomato or pepper fruit — a calcium deficiency disorder.
- Cabbage LooperRagged holes in brassica leaves made by a pale green caterpillar that loops its body as it moves.
- Imported CabbagewormRagged holes in brassica leaves with pale green caterpillars and green frass nearby.
- Why are the lower leaves on my tomatoes turning yellow?Lower-leaf yellowing on tomatoes is most often early blight, normal leaf senescence, or nitrogen deficiency — the pattern and timing tell you which one you're dealing with.
- What is that black leathery patch on the bottom of my tomatoes?Blossom end rot is a calcium deficiency at the fruit level, almost always caused by irregular watering rather than a lack of calcium in the soil.
- When is the best time to add compost to the garden?Fall is often the best time to add compost to garden beds — it has all winter to incorporate and break down further, and beds are ready to plant without delay in spring.