Bacterial canker (blossom blast)

Bacterial canker (blossom blast)

Pseudomonas syringae pv. syringae van Hall Pseudomonas syringae pv. morsprunorum (Wormland) Yound et al.


Leaf scars, stomata, and areas of injury are the principal sites of infection. The most conspicuous symptoms are limb and trunk cankers (A, B), blossom blast (C), "dead bud", and leaf spotting; these symptoms may or may not occur together. Cankers can girdle and kill entire limbs, reducing the tree's fruiting capacity. Infection of the trunk, particularly on young trees, often results in tree death. Crotches are particularly susceptible to infection, which often leads to extensive gumming (D). Infections of the blossoms cause blossom blast and loss of fruiting spurs (E). Infections of dormant flowering and vegetative buds result in a condition called "dead bud" in which buds fail to break dormancy in spring. On leaves, lesions are tan to brown and initially surrounded by a yellow halo. Lesions may be small or they may coalesce to form large areas of infection. They are eventually walled off and the center of the lesion drops out to give the leaf a shot-holed appearance (F). On fruit, lesions tend to be circular, brown, and sunken (G).

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