Alternaria solani
Common fungal disease of tomatoes and potatoes causing characteristic target-spot lesions on leaves. Reduces yield and fruit quality.
Dark brown spots with concentric rings (target-spot pattern) on lower leaves first. Yellowing around spots. Leaf drop. Dark sunken spots on fruit near stem.
Fungal pathogen that overwinters in plant debris and soil. Favored by warm temperatures and alternating wet/dry conditions.
Rain splash, wind, contaminated tools, and infected transplants. Spores produced on infected tissue spread to healthy plants.
Warm temperatures (75-85°F), high humidity, wet foliage, stressed plants (nutrient deficiency, heavy fruit load).
Rotate crops 2-3 years. Remove plant debris. Stake or cage plants. Water at base of plants. Use resistant varieties. Adequate fertilization.