Skip to content
Grow In Backyard
Plant Diseases

Black Spots on Tomato Leaves: Which Disease You Have

Septoria, early blight, bacterial spot and late blight all start as dark leaf spots. Telling them apart decides whether you prune, spray, or pull the plant.

By Salma 3 min read Save to Pinterest — opens Pinterest in a new tab
Septoria lesions spreading across a tomato leaf
Photo: Wolan268, CC0, via Wikimedia Commons
On this page

Four different diseases produce dark spots on tomato leaves, and they need different responses — including one where the correct response is pull the plant out today.

Work out which you have before you do anything else.

Identify it

Four diseases, four signatures
SeptoriaEarly blightBacterial spotLate blight
Spot sizeSmall, under ¼ inLarger, ¼–½ inSmall, angularLarge, irregular
NumberManyFew at firstManyFew, spreading fast
CentreGrey/tan, black dotsConcentric ringsGreasy, darkWater-soaked
StartsLowest leavesLowest leavesAnywhereUpper leaves often
Fruit affectedNoSometimes, at stemYes — raised scabsYes — greasy brown
WeatherWarm, wetWarm, humidWarm, wetCool, wet
Kills the plantRarelyRarelyRarelyYes, in days

The quickest tell: get close to a spot. A pale centre speckled with tiny black dots — the fruiting bodies — is septoria. Rings inside the spot like a target is early blight.

Late blight is the one that changes your day

Large, irregular, greasy, water-soaked patches that spread visibly day to day — often with white fuzz on the leaf underside in humid mornings — is Phytophthora infestans. It destroys a plant within days and travels on the wind to every tomato and potato nearby.

Remove and bag the whole plant immediately. Do not compost it, do not try to prune it out, and check your potatoes. This is the disease that caused the Irish famine, and it moves like it.

What to do about the other three

All of septoria, early blight and bacterial spot are manageable. You are aiming to slow them enough that the plant keeps fruiting until the end of the season.

1. Strip the affected leaves. The most effective single action. Remove spotted lower leaves as soon as they appear, and everything within about 12 inches of the ground. Bag them; do not compost. Prune when foliage is dry, and wipe tools between plants.

2. Mulch, heavily. Rain splashing soil onto leaves is the main infection route — these pathogens overwinter in soil and debris. Three inches of straw or wood chips breaks that path, and it is the best prevention available.

3. Water at the base, in the morning. Never overhead. Wet foliage overnight is what these diseases wait for.

4. Open the plant up. Space generously, stake or cage so nothing lies on soil, and thin congested growth so air moves through.

5. Spray only as protection. Copper fungicide is the standard organic option; chlorothalonil the synthetic one. Neither cures an existing spot — they protect leaves that are still clean, so they work when started early and largely fail when deployed on a plant already covered. Reapply after rain.

Next season

Rotate. Three years out of tomatoes, potatoes, peppers and eggplants on that ground. These pathogens persist in soil and debris, and rotation is what starves them.

Clear everything at the end of the season — every stem, leaf and fallen fruit. Debris left in place is the inoculum for next year.

Choose resistant varieties where you have had trouble. Look for early blight tolerance (Mountain Magic, Defiant, Jasper) and late blight resistance in wet climates.

Start clean. Bacterial spot in particular arrives on infected seed and transplants. Buy from a reputable source, and do not save seed from an affected plant.

If spots are only on the very lowest leaves late in the season

Some lower-leaf loss on a mature tomato is normal and not worth fighting. Strip the affected leaves, keep mulching, and let the plant finish its crop. Perfect foliage is not the goal — fruit is.

Common questions

What causes black spots on tomato leaves?

Four things account for nearly all of it. Septoria leaf spot gives many small round spots with grey centres and dark edges, starting on the lowest leaves. Early blight gives fewer, larger brown spots with concentric rings like a target. Bacterial spot gives small, angular, greasy-looking dark spots that may also mark the fruit. Late blight gives large, irregular, water-soaked greasy patches that spread fast in cool wet weather and kills plants outright.

How do you tell septoria from early blight?

Count and look at the middle. Septoria produces many small spots, typically under a quarter inch, with pale grey or tan centres and tiny black dots visible in them. Early blight produces fewer, larger spots with dark concentric rings inside them, like a target, often with a yellow halo. Both start on the lowest leaves and work upward, and both respond to the same management.

Can a tomato plant recover from leaf spot?

From septoria, early blight and bacterial spot, usually yes — they are foliage diseases that reduce yield but rarely kill. Remove affected leaves, improve airflow, mulch, and water at the base, and a healthy plant will keep fruiting. Late blight is different: it destroys plants within days and spreads to every tomato and potato nearby, so an infected plant should be removed immediately rather than treated.

Should I remove the affected leaves?

Yes, and it is the single most effective thing you can do. Take off spotted lower leaves as soon as you see them, plus everything within about a foot of the ground, and bag them — do not compost them. This removes the spore source and increases airflow at the base. Prune when the foliage is dry, and disinfect your tools between plants.

What spray actually works on tomato leaf spot?

Copper fungicide is the standard organic option and works on all four, but only as protection for healthy leaves — nothing cures a spot that already exists. Chlorothalonil is the common synthetic equivalent. Both need reapplying after rain and are far more effective started early than deployed once the plant is covered. Cultural fixes do more: mulch, spacing, base watering, and crop rotation.

How do I stop it happening next year?

Rotate out of the nightshade family for three years, since these pathogens overwinter in soil and debris. Mulch heavily so rain cannot splash spores from soil onto leaves — that splash is the main infection route. Space plants for airflow, stake them off the ground, water at the base in the morning, and clear every scrap of tomato debris at the end of the season.

Backyard Weekly

Know what to plant, week by week

Join the weekly email for seasonal jobs, fixes for what is going wrong, and gear worth buying.

Not ready to subscribe? The planting calendar is free and needs no email.

By subscribing you agree to our privacy policy. Grow In Backyard will never sell your address.

Keep reading