Cause Fire blight is caused by the bacterium, Erwinia amylovora . The bacteria overwinter in cankered limbs, and in spring, droplets of sticky, amber-colored ooze form from these cankers. These droplets contain large numbers of bacteria. Insects and spattering rain carry the bacteria from the droplets to blossoms and twigs. More fire blight bacteria ooze from these new infections, and insects and rain again carry them to new areas of the tree and orchard.
Fire blight is most damaging in years when spring temperatures are above normal with frequent rains.
During cool springs the blossoms blight phase is usually not significant. No single practice can insure complete control of fire blight. However, you can reduce the disease if you employ a combination of both cultural and chemical control measures as outlined below. Fire blight-infected limbs and branches should be pruned during late winter when there is much less chance of spreading fire blight bacteria on cutting tools. However, often it is necessary to make immediate cuts to prevent the disease from going into the main framework of the tree.