Late blight

Symptom

The disease is caused by the Phytophthora pathogen. Symptoms typically begin at the tips and edges of older leaves as water-soaked lesions. As the infection develops, these lesions enlarge, turn brown, and eventually dry out. During humid weather, these spots can darken further to a purplish-brown color and merge into larger blotches. On the underside of the leaves, a white, downy mold (sporulation of the pathogen) is often visible. Dark brown to black lesions appear on the stems, often leading to structural weakness. As the disease advances, stems may collapse or break, causing the entire plant to wilt and die. On green or ripening tomato fruits, sunken, firm, brown lesions form. These spots may enlarge and become irregular in shape, often turning dark brown or even purplish-black in moist conditions. A white fungal growth may also appear on the surface of infected fruits. Affected fruits may become soft and emit an unpleasant odor. This disease spreads rapidly and can infect the entire plant simultaneously, often resulting in plant death.