• The bacterium causing fire blight overwinters at the margins of the cankers formed on twigs and branches in the previous season.
• Active bacteria are in the healthy tissue next to the canker rather than in the canker.
• In the spring the bacteria begin to multiply at the same time growth starts. As the bacterium increases, an ooze is formed at the margin of the canker.
• Insects are attracted to the ooze and it is carried to the open blossoms. Splashing rain can also spread the bacterium.
• Once bacteria enter a blossom, the blossoms are blighted within 7-10 days after infection. After blossom infection, bacteria spread into the fruit peduncle and finally into the twig.
• Ooze is continually being produced which can add to secondary infection. During periods of high humidity, the bacteria can enter into young leaves.

Management

• Plant resistant or tolerant varieties: Kieffer, Orient, Garber, or Douglas.
• Maintain balanced fertilizer level. Do not use excess levels of nitrogen.
• Prune during dormant months. Summer pruning may encourage tender succulent growth which is more susceptible to disease.
• Remove over wintering bacteria cankers by pruning. Make pruning cuts 8 to 12 inches below visible sign of disease.
• Apply bactericides on 5 day intervals between early bloom and late blooms.
• Reapply a bactericidal spray to an orchard if it is damaged by hail or receives a heavy rain immediately after an application.