Brown or Black Spots on Tomato Leaves: What It Means and What to Do
Set your conditions — the recommendation updates instantly.
GardenSays
Most likely: Early blight (Alternaria). It's manageable if you act.
- Most likely
- Early blight
- Severity
- Act soon
- Causes checked
- 4
Based on brown or black spots on the lower leaves with moist soil, the best match is early blight (alternaria). Confirm it: Brown spots up to ½ inch with concentric target rings, yellow halo, starting on oldest leaves.
What to do: Remove affected leaves, mulch against soil splash, water at the base, rotate next year. Fungicide if spreading fast in wet weather.
If that doesn't match what you see, work down the list: Late blight (Phytophthora) (large greasy gray-green-to-brown blotches, white fuzz under leaves in humidity, spreads through the plant in days during cool wet weather.); Septoria leaf spot (many small (⅛ inch) circular spots with dark borders and light gray centers — smaller and more numerous than early blight.).
- ⚠ Late blight (Phytophthora) is a possibility — it can't be cured, so confirm or rule it out first: Large greasy gray-green-to-brown blotches, white fuzz under leaves in humidity, spreads through the plant in days during cool wet weather.
Why
- ✓A symptom tree ranks causes by how well your conditions match each cause's classic pattern — the distinguishing signs are how you confirm.
- ✓Most leaf problems trace to water, weather, or the two big leaf-spot fungi — true plant-killers are rarer but worth ruling out first.
When this doesn't apply
- →If the plant is collapsing fast (days, not weeks), treat it as late blight or wilt until proven otherwise — photograph it and check with your county extension.
- →Multiple symptoms at once usually means the top cause here plus plain stress — fix watering first, then re-diagnose.
How this was calculated
- 1. Symptom
tomato: brown or black spots — 4 known causes evaluated
- 2. Your conditions
Location on plant: lower; soil: moist. Causes matching these conditions rank higher.
- 3. 1. Early blight (Alternaria)best match (score 6)
Distinguishing signs: Brown spots up to ½ inch with concentric target rings, yellow halo, starting on oldest leaves.
- 4. 2. Late blight (Phytophthora)score 6
Distinguishing signs: Large greasy gray-green-to-brown blotches, white fuzz under leaves in humidity, spreads through the plant in days during cool wet weather.
- 5. 3. Septoria leaf spotscore 5
Distinguishing signs: MANY small (⅛ inch) circular spots with dark borders and light gray centers — smaller and more numerous than early blight.
- 6. 4. Bacterial spot/speckscore 3
Distinguishing signs: Many tiny dark specks, sometimes with yellow halos, after warm rains; fruit may show raised specks too.
Data sources
- University of Minnesota Extension — Growing tomatoes in home gardens (common problems) (checked 2026-07-15)
- UMN Extension — What's wrong with my plant? (tomato diagnostic) (checked 2026-07-15)
- Cornell Vegetables — Disease factsheets (checked 2026-07-15)
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