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Cornell University : Cornell Cooperative Extension
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| Yates Association |
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Fire Blight of Fruit Trees |
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Fire blight is an extremely destructive bacterial disease of more than 75 species of trees and shrubs. Among the plants attacked are apple, pear and quince. Fire blight attacks succulent tissues of blossoms, shoots, watersprouts, and root suckers. Infections may extend into scaffold limbs, trunks, or root systems, and may kill the tree. Fire blight overwinters in cankers that usually appear as darkened depressed areas on the bark. Cankers formed late in the season normally lack detectable margins and are likely to harbor overwintering bacteria. They vary in size and can be found on any woody part of a tree. The bacterium resumes growth in the spring. The fire blight pathogen is spread by insects and rain. Flying and crawling insects pick up the bacteria on their bodies, and then spread the inoculum to other sites. Honey bees, other insects that visit blossoms, aphids, plant bugs, and pear psylla all serve as vectors of the pathogen. Rain may wash bacteria from cankers or infection sites to new infection sites. The bacterium can also be spread on pruning instruments used in the orchard. Infections may be first observed just after bloom. Infected blossom clusters rapidly wilt and take on a brown or black, scorched appearance. The symptoms of twig blight are similar. To reduce the incidence and severity of fire blight, practice plant sanitation: carefully remove and dispose of infected branches or fruit as soon as they appear, starting one to two weeks after bloom. Cut at least 6-12 inches below obvious signs of infection and dip your pruning shears into a 10 percent bleach solution between each cut. Prune out any remaining cankered branches during the dormant season. Avoid high rates of nitrogen fertilizer or other practices that stimulate lush vegetative growth and plant less susceptible cultivars. Dormant and bloom sprays of Bordeaux mixture should be used to prevent infections. Cornell
Cooperative Extension Yates Association |
