Tomato Black Spots on Leaves and Fruit

Septoria leaf spot is one of the most common reasons for black spots on tomato leaves in UK gardens. Caused by the fungus Septoria lycopersici, it almost always begins on the lowest, oldest leaves close to the soil, because spores splash up from infected leaf debris and the soil surface. The RHS advises removing affected leaves promptly, mulching the base of the plant to reduce soil splash, and watering at the base to keep foliage dry. Michigan State University Extension describes the spots as small (up to 6 mm), dark-bordered and often with a pale grey or tan centre — numerous and clustered, unlike early blight's larger ringed spots.

Stop it coming back:Spotted leaves will not clear. Look for clean new growth over the next 10–21 days and slower spread of spots. The plant can still produce a good crop if enough healthy foliage remains.

strip every leaf from the plant — tomatoes need foliage to feed the crop and shade fruit. Do not spray with unapproved homemade mixtures such as vinegar, strong bicarbonate or washing-up liquid.

Early blight, caused by the fungus Alternaria solani, produces larger spots than Septoria — typically 6–12 mm across — with distinct concentric rings that give a target-like appearance. The same Alternaria fungus also affects related crops, so the symptoms closely mirror early blight on potatoes. It begins on lower leaves, leaves around the spots turn yellow, and in severe cases dark lesions develop on stems and the area around the stem attachment on fruit. The University of Maryland Extension notes that early blight can appear at any time during the season but is most damaging on older or stressed plants in warm, damp weather. UK growers see it most in warm, humid summers in greenhouse conditions.

Stop it coming back:Spread should slow within two weeks if caught early. Existing damaged leaves will decline, but new leaves should emerge cleaner once conditions improve.

assume extra fertiliser will resolve ringed spots — feeding can support growth but will not remove a fungal infection. Do not water from above in the evening.

Bacterial diseases on tomatoes cause very small, pepper-like dark specks on leaves, stems and sometimes fruit. The spots often have yellow halos and may appear on both leaf surfaces. On fruit, specks may be slightly raised or scabby. These diseases are more common after wet, cool-to-warm weather and can spread rapidly when plants are handled while wet. They are distinct from Septoria and early blight by the much smaller spot size and the simultaneous appearance on fruit as well as leaves.

Stop it coming back:Bacterial spotting is difficult to reverse in a wet season. Protect new growth and reduce spread. If the plant is badly affected early, replacement may be more practical than nursing a weak crop.

compost infected fruit and leaves in a cool home compost heap. Do not mist greenhouse tomatoes, as wet foliage aids bacterial spread.

Blossom end rot appears as a dark, sunken, leathery patch at the bottom (blossom end) of the tomato — opposite the stem. It often starts as a pale water-soaked area that darkens to brown or black. It is extremely common in UK grow bags, pots and greenhouse beds where watering fluctuates. The RHS and Iowa State University Extension both explain that blossom end rot is caused by calcium not reaching the developing fruit — but the problem is almost always irregular watering preventing calcium uptake, not a lack of calcium in the soil itself.

Stop it coming back:Damaged fruit will not recover. New fruit on the next truss can develop normally once watering is steady.

add crushed antacids, milk or eggshells as an emergency calcium remedy — blossom end rot is primarily a water distribution problem, not a simple calcium deficiency. Foliar calcium sprays do not reliably help fruit that is already affected.

Sunscald begins as a pale, whitish patch on the sun-facing side of tomato fruit that has been suddenly exposed to strong sunshine — typically after heavy pruning removed the shading leaves, or after a disease stripped the foliage. The affected area becomes papery, tan, brown or black as tissue dies and secondary rots move in. This is more common in greenhouses where full sun comes through on a hot day.

Stop it coming back:Marked fruit will not heal. Prevention is immediate once leaf cover and shade are restored.

defoliate tomato plants to speed ripening in hot weather — bare fruit is far more vulnerable to sunscald and secondary disease.

Spider mites cause fine pale stippling that turns yellow then brown, often with webbing visible under leaves in warm, dry greenhouse conditions. Aphids and whitefly cause sticky leaves, distorted growth and yellowing. Pest damage may be mistaken for black spots when dead tissue or sooty mould develops over feeding damage. Identifying the pest correctly is essential — biological controls in a greenhouse are very effective for whitefly (Encarsia formosa) and spider mite (Phytoseiulus persimilis) if introduced early.

Stop it coming back:Pest numbers can reduce within days after washing or biological control. Damaged leaves remain marked, but new growth should look cleaner within two to three weeks.

use broad-spectrum insecticides without identifying the specific pest — they may harm beneficial insects and can make spider mite problems significantly worse.

Older lower leaves yellowing evenly with few or no distinct spots is often normal — tomato plants shed lower leaves as the season progresses and the canopy rises. It can also indicate general nutrient stress or a watering problem (either too dry or too wet at the roots) rather than an infectious disease. This is common in pots and grow bags that have been repeatedly dry or waterlogged. The absence of distinct lesions with defined borders is the key distinguishing feature.

strip all yellowing leaves from a small plant — partly green leaves still contribute to photosynthesis. Do not overfeed with nitrogen in response to yellowing without first checking root health and soil moisture.