Bacterial blossom blast of pear
Pseudomonas syringae pv. syringae van Hall
The most common symptoms are wilting followed by browning or blackening of blossoms, often spreading through the entire blossom truss and killing the fruiting spur (A, B). If infection is restricted to the calyx-cup and the blossom is not killed, this may lead to the development of black lesions on developing fruit; many of these fruit drop. Infection of the leaves leads to the development of small lesions and "shot holes"; entire leaves may be killed.
Common to all fruit-growing regions in eastern North America; most common in cool and wet climates.
Blossom blast can be confused with fire blight. However, fire blight infections often lead to extensive damage of shoots and limbs, and will often be found in neighboring apple orchards; P. syringae pv. Syringae does not affect apple.
Blossom blast is a problem when cool and wet weather prevail during bloom, especially when blossoms are injured by a light frost. The disease is difficult to manage. The application of copper-based bactericides is the only practical control option. Streptomycin applied to control fire blight may reduce disease severity.
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