Early blight of potato

Symptom

Small dark brown to black spots appear first on older (lower) leaves. Spots enlarge and develop concentric rings, forming a "target" or "bull's-eye" pattern this is the hallmark of early blight. Surrounding tissue often turns yellow, creating a halo effect. As lesions grow and merge, they cause large necrotic areas, leading to leaf wilting and drop. Severe infections cause premature defoliation, reducing the plant's ability to photosynthesize and impacting yield. Elongated, dark brown to black sunken lesions can form on stems and petioles. In advanced stages, stem lesions can girdle the stem, causing wilting or even death of the upper plant parts. Infection on tubers results in sunken, dry, dark brown  to black lesions with raised margins. The underlying flesh becomes dry and corky, often forming a hard boundary between healthy and diseased tissue.