Early Blight
Alternaria solani, Alternaria tomatophila
Overview
A common fungal disease of tomatoes and potatoes causing dark, concentric-ringed lesions on lower leaves that progress upward. Also known as Alternaria blight.
Symptoms
Dark brown to black lesions with concentric rings (target-like pattern) on lower leaves first. Lesions may appear on stems and fruit. Lower leaves yellow and drop. Fruit develops dark, leathery sunken spots near the stem end.
Environmental Conditions
Humid
Prevention
Rotate crops on a 3-year cycle. Use certified disease-free seed. Stake or cage plants for air circulation. Mulch to prevent soil splash. Remove lower leaves touching the ground.
Management
Apply copper-based fungicides or chlorothalonil at first signs. Remove infected lower leaves. Improve air circulation. Avoid overhead irrigation. Harvest fruit promptly when ripe.