Late Blight

fungus

Phytophthora infestans

Devastating water mold disease of tomatoes and potatoes. Caused the Irish Potato Famine. Spreads rapidly in cool, wet weather.

Identification

Large, dark, water-soaked lesions on leaves and stems. White fuzzy growth on leaf undersides in humid conditions. Firm brown rot on fruits.

Rapid defoliation and plant death. Fruit rot. Potato tuber rot. Can destroy entire plantings in days.

Copper fungicide (preventive only). Remove and destroy infected plants immediately. Do NOT compost.

Chlorothalonil (Daconil). Mancozeb. Must be applied preventively.

Resistant varieties. Avoid overhead irrigation. Space plants for airflow. Do not plant tomatoes near potatoes. Remove volunteer potatoes.

Data confidence: medium | Source: curated_ipm