Early Blight
Disease · Commonly affects: Tomato, Potato, Eggplant, Pepper
Early blight is a common fungal disease of tomatoes and potatoes caused by the fungi Alternaria solani and Alternaria tomatophila. It matters to home gardeners because it shows up nearly every season in warm, humid weather, gradually stripping plants of their foliage and reducing yield.
How to identify it
Look for small brown to black spots on the oldest, lowest leaves first, often the size of a pencil eraser or larger. A classic sign is the concentric rings inside the spots that give a target or bullseye pattern, usually surrounded by a yellow halo. On tomatoes you may also see dark, sunken lesions with rings on the stems and near the stem end of the fruit.
Damage
As spots enlarge and merge, infected leaves yellow, die, and drop, working upward from the bottom of the plant. This loss of foliage weakens the plant, cuts down on the energy it can make, and exposes fruit to sunscald that lowers both quality and the total harvest.
Prevention
Rotate tomatoes and potatoes out of the same bed for at least two to three years, and avoid planting them where related crops grew recently. Space plants well and stake or cage them for good air movement so leaves dry quickly after rain or dew, and choose varieties labeled as resistant or tolerant to early blight. Clean up and remove plant debris at the end of the season, keep the garden weed free, and build healthy soil with balanced fertility and steady moisture so plants are less stressed.
How to manage it
Prune out and remove affected lower leaves as soon as you spot them, and pull severely infected plants to slow the spread, putting all diseased material in the trash rather than the compost pile. Mulch around the base of plants to keep soil from splashing spores onto the leaves, and water at the soil line with a soaker hose or drip early in the day so foliage stays dry. Work among plants only when leaves are dry, and disinfect pruners between plants to avoid carrying the fungus.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.