Alternaria blight

Important species:
- Alternaria leaf spot on tomato; Alternaria stem canker (A. alternata);
- Alternaria leaf spot on cole crops; Alternaria blight (A. brassica; A. brassicicola);
- Leaf blight of carrot; Black rot of carrot (A. dauci; A. radicina).
Host plants: crucifers, tomato, carrots, beans are the most susceptible crops but will also infect other herbaceous plants.
Symptoms. Alternaria fungus is transmitted through seeds (seedborne). The fungi colonize the seed coat during the seed development stage and when the seed germinates, they become active. The fungal disease causes damping-off and stunted seedling. Infection develops so slowly that a symptom only appears when the seedlings are transplanted in the field. The leaf spots vary in sizes from very tiny spots up to 5 cm in diameter. The spots begin as small yellow or brown spots that slowly enlarge to about 5 cm in diameter, dark colored spots with concentric rings. When all the spots join together, the leaves will turn yellowish or blackish and drop off.