Bacterial Blight of Chrysanthemum caused by Erwinia Bacterial blight Bacterial blight of chrysanthemum is caused by Erwinia chrysanthemi and Erwinia carotovora . Erwinia is an opportunistic plant pathogen causing soft rot diseases of many ornamental and vegetable crops, especially during periods of high moisture and warm temperatures when plants have fresh wounds. Soft rot is especially common during rooting of cuttings. The entire cutting may become affected within several days. In larger plants, symptoms usually occur in the stem terminals.
Stems become greyish and are soft and easily collapsed with the fingers.
Wilting is usually evident at this time. Diseased tissues become brittle as they dry out. Brown to black lesions will form on the outside of the stem as the bacterium rots through to the surface. These external cankers can be mistaken for those caused by Pseudomonas cichorii . However, P. cichorii cankers are firm and originate at flower buds or leaves.