How to Identify Early Blight, Late Blight, and Leaf Spot on Tomatoes

Early blight, late blight, and leaf spot are common fungal diseases of tomato plants.

Late blight is the most serious of the three. It spreads rapidly and will likely destroy the infected plant and can quickly spread to other plants—including potatoes, eggplants, and peppers.

Here are the basics for identifying these fungal diseases:

Conditions for disease growth

Early blight: high humidity; temperatures above 75°F; transmission hastened by wind, heavy dew, and frequent rain; poor plant nutrition contributes.
Late blight: high humidity; temperatures between 60° and 80°F; wind-, rain-, and soil-borne. Infection often occurs before blossoming. Spores germinate readily at about 70°F. Watch for disease when cool, moist nights are followed by warm, muggy days.
Leaf spot: high humidity; temperatures between 60° and 80°F.

Leaf symptoms

Early blight

Symptoms appear first on older, mature leaves near the base of the plant–one or two spots per leaf, spots ¼ to ½ inch in diameter; spots have tan centers with concentric rings and yellow halos around the edges, target-shape appearance with defined border; spots enlarge and coalesce. A large portion of the leaf becomes a diffuse yellow and may drop. No mold appears. The disease spreads slowly.

Late blight

Water-soaked spots show first on lower leaves; spots start out pale green diffuse irregular spots on the upper side of the leaf, usually near the edges of tips of leaves; spots turn brown to purplish-black and velvety with a pale green border on the underside of the leaf; spots appear on young leaves at the top of the plant; spots look water-soaked; no concentric rings or defined border around necrotic spots. In humid, wet conditions, a fuzzy ring of mold around the spot appears on the undersides of the leaves. Leaves shrivel, turn brown, and die. The disease spreads rapidly.

Leaf spot

Numerous brown spots appear on the leaves 1/16 to 1/4 inch in diameter; spots are circular with dark brown margins and tan to gray center–a black speck in the center; spots do not have a yellow halo. The disease spreads upwards from oldest to youngest. Leaves turn slightly yellow, then brown, then wither.

Stem symptoms

Early blight

Dark, sunken lesions appear on the stem at or above the soil line, sometimes called collar rot.

Late blight

Black and brown lesions appear on the stem and petioles; when petioles or leaf stalks are affected, the entire leaf can collapse; the entire vine or plant can quickly collapse and die in periods of high humidity.

Leaf spot

There is no stem damage.

Late Blight on Tomato — Late blight on tomato fruit

Fruit symptoms

Early blight

Sunken spots appear on the stem end of fruits; concentric ring pattern or target-shape appearance around spots; disease moves from stem to rot fruit.

Late blight

Spots beneath the skin develop on tops and upper sides of green fruit; spots become reddish-brown, firm, dry, and leathery; spots grow larger; the skin wrinkles and darkens to chocolate brown; soft rot sets in; white mold forms in damp, humid conditions.

Leaf spot

Fruit is usually not affected; sunscald may occur as a result of leaf loss above.

Treatment of disease

Early blight

Remove lower leaves after first fruit sets; then remove affected leaves as they appear; plant in a different location next year.

Late blight

Pull and destroy the plant as soon as you know its late blight; select resistant varieties to plant in the future; plant in a different location next year.

Leaf spot

Remove infected leaves as they appear; improve air circulation around plants; clean tools after use; clean plant stakes and cages; plant in a different location next year.