Taxonomy: Bacterial, (Pseudomonas syringae pv. tabaci)
Description: Initial symptoms are small circular pale-green areas (0.5 cm in diameter) which become brown in the centre due to death of the leaf tissues. The necrotic process advances rapidly and the yellowing halo extends. Within a few days spots can enlarge up to 3 cm in diameter, with a water-soaked zone surrounding the necrotic centre. Badly infected leaves grow badly and become distorted. 
Control general remarks: Crop rotations are important. Use a soil sterilant (fumigant) in the seed beds.