Pseudomonas syringae survives and grows on the surface of many different plant species and is distributed by splashing rain and by insects. Severe outbreaks of blossom blast on pears are usually associated with spring frosts because frost injury provides entry sites for infection. Symptoms of pear blast include blackening of the calyx end of individual fruitlets, blackening of entire blossom clusters with cluster leaves remaining unaffected, or complete death of clusters including both the blossoms and the leaves. Young leaves near affected clusters may have small nondescript necrotic leaf spots. Unlike fire blight, blossom blast does not spread into larger limbs or cause extensive damage to pear trees.
Infections can seriously reduce fruit set.
Pear blast has been a significant problem in Oregon where the pear producing region commonly has cool, wet weather that persists during long, extended bloom periods. Researchers and pear growers in Oregon have noted that orchards severely affected by pear blast one year are more likely to be affected again in subsequent years. The recommended control for this disease in Oregon has been application of a dormant copper spray followed by two applications of streptomycin during the early part of the bloom period using the labelled timing and rates indicated for fire blight. Pear blast has been only a sporadic problem in New York, with severe outbreaks usually occurring in years when light frosts occurred during bloom. There is no recent research on pear blast in eastern United States, so we can only base control recommendations on older data and on experiences in other regions.