Early Blight Figure 3. As in Septoria leaf spot, the spores that cause early blight overwinter in last year's garden crop debris. This disease occurs in midsummer during warm, humid periods. Fungus spores that come in contact with a water droplet on the leaf germinate and ultimately infect the leaf. Symptoms appear on leaves about 10 days after infection.
Symptoms also can appear on stems and fruit.
Key Symptoms Irregular, dark brown areas on leaves that show concentric, black rings in a target-like pattern. Yellowing around the necrotic area. Disease Management Follow disease management practices outlined for Septoria leaf spot. Remove badly diseased leaves during the growing season. Bacterial Speck and Bacterial Spot Figure 4.