Disease

Early blight and Alternaria leaf spot

Alternaria solani, A. linariae, A. brassicicola

A soil- and seed-borne fungus that starts on the oldest leaves and works up the plant. Splashing water spreads it, and warm, humid weather with long dew periods speeds it up.

Early blight: brown target spots with rings on a tomato leaf Photo: Clemson University - USDA Cooperative Extension Slide Series, CC BY 3.0, via Wikimedia Commons

Signs

Brown spots up to half an inch across with concentric rings, like a target.
A yellow halo around each spot; heavily spotted leaves turn brown and drop.
Black, leathery spots near the stem on tomato fruit; dark collar rot at the stem of seedlings.

What favors it

Warm, humid weather, long dew periods, splashing water, and older plants. The fungus survives on debris and seed.

Prevention

Rotate out of the tomato and potato family for at least two years.
Mulch to stop soil splashing; water at the base.
Stake or cage for airflow; remove the lowest leaves once plants are established.

Crops it shows up on

Tomato, pepper & eggplant; Potato.

Often confused with

DiseaseSeptoria leaf spot DiseaseLate blight DiseaseBacterial leaf spot NutrientPotassium deficiency

Sources

Early blight in tomato and potatoUniversity of Minnesota Extension
Early Blight of TomatoesUniversity of Maryland Extension
Tomato leaf spot diseasesUniversity of Minnesota Extension

Why →

Treatment by crop

Cultural, biological and chemical options in the order to use them, and notes written for each crop.

Identification is free. Treatment is on the Home and Pro plans.

Open in the key See plans

Look the plant over, leaf undersides included. Are insects, mites, slugs, eggs, webbing or droppings on it?
No, only damage or discoloration
Where is the problem?
Leaves
What does the leaf damage look like?
Distinct spots or lesions
Where on the plant are the spots?
Older, lower leaves first, moving up
What do the spots look like?
Brown spots with rings, like a target

Not a match? Start the key or describe what you see.

Early blight on lower leaves Photo: Jerzy Opioła, CC BY-SA 4.0, via Wikimedia Commons

Early blight lesions on the stem Photo: Clemson University - USDA Cooperative Extension Slide Series, CC BY 3.0, via Wikimedia Commons

More from university Extension: search Extension pages on early blight and alternaria leaf spot, or find a plant diagnostic lab through your state's Extension.

Early blight and Alternaria leaf spot

Signs

What favors it

Prevention

Crops it shows up on

Often confused with

Sources

Questions in the key that lead here

More photos

Other diseases