The fire blight bacterium (Erwinia amylovora) often afflicts the evergreen pear tree (Pyrus kawakamii). The disease occurs widely throughout the eastern United States. A popular ornamental tree, the evergreen pear tree grows to a height of 25 feet and produces a profusion of white flowers each spring. The glossy green foliage remains on the tree all year, making the tree a popular wintertime landscape specimen. Unfortunately, a tree afflicted with fire blight suffers rapid decline.
Fire blight occurs in regions that have warm springs with humid summer nights, according to the Urban Forestry South Expo at the University of Georgia. The bacterium causes the new twigs and small branches of the evergreen pear tree to blacken and shrivel. The foliage will wilt on affected branches. The blossoms of the tree turn black and wilt. If the disease is not treated it will advance to the main branches and trunk of the evergreen pear tree causing oozing cankers to form. The entire tree appears to have sustained damage from a fire when heavily infected.
The bacteria of fire blight lives within the infected tissue of the evergreen pear tree and other host species. During the warm, moist weather of spring the cankers of the afflicted tree begin to ooze a tan substance. The substance contains the rapidly multiplying bacteria of the fire blight. Insects which come into contact with the oozing cankers can help spread the bacteria to other trees. Splashing rain can also spread the bacteria.
Mode of Infection
During spring the bacteria can enter the evergreen pear tree through wounds sustained from pruning, from overcultivation or through the flowers. Once the bacteria establishes in the flowers they immediately begin to wilt and take on a water-logged appearance. The bacteria spreads upwards from the flowers into the twigs rapidly.
Promptly prune away all areas of the evergreen pear tree afflicted with fire blight. Prune back until healthy wood is reached. Promptly dispose of infected branches so they do not inadvertently infect nearby trees. Dip the pruning shears into a mixture of bleach and water between each pruning cut to sterilize the shears and keep them from spreading the fireblight bacteria to other areas of the tree.
Consider spraying the evergreen pear tree during dormant months with neem oil, copper sulfate or bordeaux mix to help control any overwintering fireblight pathogens. Maintain the evergreen pear tree with regular fertilizer applications in the spring, summer and fall. Use a general purpose fertilizer, such as a 10-10-10. Avoid subjecting the tree to extended periods of drought. A healthy evergreen pear tree will be able to successfully recover from fire blight with care, but an unhealthy tree may die from the bacteria.