The best course of action is to select crabapples which are resistant or tolerant to this disease. Fireblight This devastating disease is caused by a bacterium, Erwinia amylovora. Symptoms appear as death of new terminal shoots in late spring or early summer. These shoots appear to be scorched by fire. Fireblight often progresses down through the shoot and forms a canker in the older tissue.
Cankers are typically sunken areas that are dark brown to purplish in color.
An orange or amber gum may ooze from these infected parts. As the bark dies, the area becomes slightly depressed. Control of fireblight can be easily achieved if these guidelines are followed. First and foremost, select plants that are genetically resistant to fireblight. If that is not an option then sanitation, removal, and disposing of blighted branches and shoots are the best alternatives.