Plant Problem Diagnostic
Early Blight: How to Identify and Manage It
The short answer
Early blight, caused by the fungus Alternaria solani, first appears as small dark spots on older, lower leaves. The spots enlarge to about half an inch with target-like concentric rings and a yellow halo, and severely infected leaves brown and drop. The least-toxic controls are cultural: stake or trellis plants for airflow, mulch to stop spores splashing up from the soil, prune the lowest leaves, keep foliage dry, and rotate away from tomato and potato for a couple of years.
No variety is fully resistant, though some are more tolerant. If early blight is severe or persistent despite good practices, a protectant fungicide program may be warranted; consult your local Extension office for current recommendations and to confirm the diagnosis, since early blight can be confused with other leaf spots.
How to identify early blight
Look on the oldest, lowest leaves first for round brown spots with concentric rings, like a target, surrounded by yellowing tissue. It typically works its way up the plant.
- Dark spots with target-like concentric rings on lower leaves
- Yellowing around the spots; leaves brown and drop
- Common in warm weather that alternates wet and dry
Least-toxic management, in order
- 1Airflow — Stake or trellis plants to increase air movement and speed leaf drying.
- 2Mulch — Mulch the soil to keep spores from splashing up onto lower leaves.
- 3Prune lower leaves — Remove the lowest, most-infected leaves as the plant grows.
- 4Keep leaves dry — Water at the base rather than overhead to reduce leaf wetness.
- 5Rotate crops — Rotate away from tomato and potato for two to three years to lower inoculum.
When to escalate
Escalate to a preventive protectant fungicide program only when cultural steps are not holding the disease and a crop is at risk. Because early blight resembles Septoria leaf spot and other issues, confirm with your regional Extension office before treating.
✔ There is no fully resistant variety, but some tomatoes are more tolerant; pairing a tolerant variety with sanitation reduces how often you need to spray.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- University of Minnesota Extension — Early blight in tomato and potato — Target-like spots on lower leaves, cultural controls (trellising, mulch, pruning, dry leaves, rotation), and tolerant varieties
- NC State Extension — Early Blight of Tomato — Alternaria solani cause and characteristic concentric-ring lesions