Notes on Apple Diseases
Blister spot
Identification
Blister spot is a bacterial disease of apples, particularly the cultivar
Mutsu (Crispin). Symptoms first appear as small lesions on the lenticels
of fruit in mid-to-late July. The lesions continue to expand during the
growing season. Near harvest they have blistered brown centres with a
dark purple border.
Period of activity
Fruit infection occurs shortly after petal fall. By late July the bacteria
can no longer penetrate the cells so infections are less likely to occur.
Thresholds
There is no threshold for this disease.
Management notes
Select disease-free nursery stock to reduce problems with this disease.
Aliette and copper are effective to reduce the level of infection; however,
repeated sprays are necessary.
Be aware of susceptible varieties. See Examples of Apple Cultivars Susceptible
to Key Diseases, for more information.
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