Small, dark, angular spots on the lower leaves after a stretch of wet, humid weather are almost always bacterial spot or bacterial speck, two related but distinct diseases that behave the same way in the garden. Both spread fast in rain and overhead watering but rarely kill a plant outright. Check the lower leaves and the fruit shoulders before reaching for a fungicide meant for early blight, since neither of these bacterial diseases responds to it.
What you are looking at
Bacterial spot and bacterial speck both start low on the plant and move upward as splashing water carries bacteria from the soil onto new leaves. Neither one kills a tomato plant outright, but a bad case in a wet season can strip enough foliage to sunscald the fruit and cut yield. The two diseases look almost identical to the naked eye, and telling them apart matters less for treatment than telling them apart from the other blights, which we cover in the next section.
Leaf Spots
Look at the oldest leaves first, the ones closest to the soil. The lesions are small, angular, and dark, often bounded by the leaf veins so they look like they have straight edges rather than the round spots of a fungal disease. A yellow halo usually rings each spot, and in humid mornings the lesion surface looks slightly water-soaked or greasy. As the disease progresses, spots merge into larger dead patches and whole leaflets yellow and drop, working steadily up the plant.
Fruit Lesions
Fruit infection is one of the clearest tells that you have a bacterial disease rather than a fungal one. Bacterial spot produces raised, dark, scabby lesions with a slightly sunken center, mostly on green fruit that never fully smooth out even as the fruit ripens around them. Bacterial speck instead leaves tiny, flat black specks, sometimes ringed by a faint pale halo, scattered over the shoulder of the fruit. Both stay shallow and superficial. The flesh underneath does not rot, which is different from what you would see with a fruit-rotting fungal disease.
Stem and Petiole Lesions
Under heavy pressure, the same dark, water-soaked streaking shows up on stems and leaf petioles, running lengthwise rather than as a round spot. These streaks look faintly greasy when fresh and dry to a dark scar later. They rarely girdle a stem the way a canker disease does, so a plant with streaked petioles and stripped lower leaves is still usually salvageable.
What it is not
Getting the identification wrong here is the costly mistake, not missing the disease altogether. A gardener who treats bacterial spot as early blight wastes a fungicide application that does nothing to a bacterial pathogen. A gardener who treats bacterial canker as bacterial spot loses the whole plant while trying to nurse it along, because canker is systemic and incurable once it is inside the vascular system.
Early Blight
Early blight lesions are larger, often reaching half an inch across, and show concentric rings like a archery target inside the dead tissue, something bacterial spot and speck never produce. The yellow halo is wider and the lesion itself is round rather than angular. Early blight is fungal, so a copper or chlorothalonil fungicide labeled for it will actually slow its spread, unlike with the bacterial diseases here. For a full picture of that disease, see Early Blight on Tomatoes: The Ringed Spots That Climb From the Bottom.
Septoria Leaf Spot
Septoria produces many more spots per leaf than bacterial spot does, and each one has a pale tan to gray dead center with tiny black specks visible inside, which are the fungus’s fruiting bodies. There is no ringed pattern and no angular edge, just crowded round spots on the lower canopy. It is a nuisance disease that thins the plant but rarely threatens the harvest, and the identification is covered in detail in Septoria Leaf Spot: The One People Mistake for Blight.
Bacterial Canker
Canker is the one that matters most to catch correctly. Its hallmark is a one-sided scorch along a leaflet’s margin, the outer edge browning while the center of the same leaflet stays green, unlike the diffuse spotting of bacterial spot and speck. Slice a stem open and a canker-infected plant shows a brown discolored ring just under the skin. There is no cure once canker is established, and infected plants should be removed rather than treated.
| Condition | Lesion shape | Halo | Fruit sign | Key tell |
|---|---|---|---|---|
| Bacterial spot / speck | Small, angular | Narrow yellow ring | Raised scabs or black specks | Water-soaked, greasy edge |
| Early blight | Round, larger | Wide yellow ring | Dark leathery rot near stem end | Concentric target rings |
| Septoria leaf spot | Small, round, numerous | Thin dark rim | Rarely affects fruit | Black specks inside each spot |
| Bacterial canker | Marginal scorch | None | Bird’s-eye spots, rare | Brown ring in cut stem |
Where it comes from and when it strikes
Bacterial spot is caused by several species of Xanthomonas, and bacterial speck by Pseudomonas syringae pv. tomato. Both survive between seasons on infected seed, on volunteer tomato plants, on crop debris left in the soil, and on nearby weeds in the nightshade family. They arrive on a new planting mainly through infected transplants bought or started from contaminated seed, and once established, they spread within a garden by splashing rain, overhead irrigation, and even by hands and tools brushing wet foliage.
The weather that favors each
The two diseases split along temperature lines, which is one of the few reliable ways to guess which one you have without a lab test. Bacterial spot generally favors warm, humid weather, while bacterial speck favors cooler, wet conditions, often showing up earlier in the season during cool spring rains and fading as summer heats up. Both need extended periods of leaf wetness, whether from rain, dew, or a sprinkler running in the evening, to infect a leaf at all. Wind-driven rain can carry bacteria a short distance between plants, but long-distance spread almost always traces back to infected seed or transplants rather than wind alone.
What to do about it now
There is no cure that reverses damage already done to a leaf or fruit, and no spray, chemical or otherwise, that kills bacteria already established inside plant tissue. What you do now is about slowing spread, not curing what is already infected.
Steps that actually help
- Stop overhead watering immediately and switch to soaking the soil at the base of the plant.
- Remove the worst-affected lower leaves and destroy them, rather than composting, since home compost rarely gets hot enough to kill the bacteria.
- Avoid working around wet plants. Handling wet foliage is one of the fastest ways to spread bacteria from plant to plant on your hands and tools.
- Improve airflow by staking, pruning suckers, and spacing plants further apart if you are replanting nearby.
- A copper-based bactericide applied early and repeated on a schedule can slow new infections, though it will not clear existing lesions.
The fruit itself remains safe to eat even with cosmetic lesions. Cut away the scabby or specked spots and the rest of the tomato is unaffected, since the bacteria stay confined to the surface layer and do not invade the flesh.
Keeping it out next season
Rotation works against these bacteria, but it takes patience. Both pathogens survive in old plant debris in the soil, and a two to three year break from tomatoes and peppers in the same bed gives that debris time to break down enough that it no longer carries a meaningful infection load. Shorter rotations mostly just move the problem around the yard.
Resistant cultivars and clean sourcing
Resistance to bacterial spot and speck is far less common in home garden seed catalogs than resistance to fungal diseases like Fusarium (marked F) or Verticillium (marked V), because the bacteria have multiple races and resistance genes cover only some of them. A few hybrids are bred specifically with tolerance to certain bacterial spot races, including ‘Plum Regal‘ and ‘Crista’, both roma-type tomatoes developed for commercial growers but available through some home garden seed sources. Neither offers complete immunity, so sanitation still matters more here than it does with, say, Fusarium wilt.
Buy transplants or seed from a source that tests for bacterial pathogens rather than saving your own seed from an infected plant, since the bacteria travel on seed coats. Disinfect stakes, cages, and pruning tools between seasons, since dried bacterial residue on a wooden stake can survive over winter and reinfect next year’s crop. A layer of mulch under the plants blocks the main splash pathway from soil to lowest leaves, and pruning the bottom foliage to keep it off the ground does the same job from the plant’s side. For a broader look at how this disease fits alongside the others tomatoes get, see tomato diseases.
Common questions
Can I still eat tomatoes with bacterial spot on them?
Yes, cut away the scabby spots and eat the rest. The lesions stay on the surface and do not spoil the flesh underneath.
Will copper spray actually get rid of bacterial spot?
No, copper only slows new infections on healthy tissue, it does not clear lesions that already exist. Once a leaf is spotted, that leaf stays spotted.
How do I know if it’s bacterial spot or bacterial speck?
Look at the fruit if any is affected. Raised scabby lesions point to bacterial spot, while tiny flat black pinpoint specks point to bacterial speck. Treatment for both is identical, so the distinction matters more for record-keeping than for what you do next.
Is it safe to save seed from a plant that had bacterial spot?
It is risky. Both bacteria can travel on the seed coat, and seed saved from an infected plant can carry the disease straight into next year’s transplants even if the seed looks clean.