This disease needs to be prevented; it cannot be chemically cured
This bacterial disease affects only rose-family plants, among them apple, pear (including ornamental flowering pear), hawthorn, and pyracantha. The infection enters through blossoms, then spreads with the help of pollenizing insects and splashing water from rain or sprinklers. Temperatures above 60 degrees F/16 degrees C and high humidity favor fireblight. When a shoot suddenly dies or blackens as if scorched by fire, fireblight is the likely cause.
To prevent fireblight, avoid growing susceptible plants; or plant resistant varieties. If you see infected limbs or branches, immediately cut them out; make cuts at least 1 foot below the diseased area and disinfect tools between cuts.
There is no chemical control.