PDC, University of Missouri - Fire Blight of Flower Pear


	PDC Plant Disease Profile *Fireblight*

(Please also see MU Guide G6020.)

Cause: The bacterium, Erwinia amylovora

Primary Hosts In Missouri: Pear, apple, crabapple, pyracantha, cotoneaster, Callery Pears (Flowering ornamental pear)and other members of the rose family

Symptoms / Diagnosis: The severity of the symptoms are dependent upon the cultivar and weather conditions at the time of infection, but symptoms typically include rapid death of shoot tips in spring. Symptoms typically include branch tip dieback. Affected branches turn black as if scorched by fire and are bent over in the diagnostic shepard's-crook (Figure 1). Brown to blacken, slightly sunken cankers form on the stems. The cankers are typically smooth, but cracks occur on the margins of the canker. The sapwood underneath the canker is streaked or uniformly blackened. In contrast freeze injured tissue does not show this streaking or blackening. Infections usually begin in the blossoms and cause the tissue to become water soaked, shrivel and quickly turn brown. Infection progresses into the peduncle, flower spurs and into the twig. Blighted peduncles, immature fruit and spurs also shrivel and turn almost black. Spurs and mummified fruit can remain attached to the tree for months. In some less susceptible cultivars the damage may be limited to only the flowers or cause scattered leaf blackening . In highly susceptible cultivars the bacteria progress into the twigs to cause significant dieback (Figure 2). Symptoms are typically reported to be more severe in older rather than younger trees.
Because freeze injury does resemble fire blight injury it is not safe to assume that all tip dieback is related to fire blight. A laboratory diagnosis involves the observation of bacteria and culture from the diseased tissue for positive confirmation.

Life Cyle: The bacteria overwinter in tissues surrounding twig and branch cankers. During wet, humid weather in early spring, the bacteria ooze from these cankers. This is attractive to insects, particularly honeybees and they spread the bacteria within the tree as well as to others as they visit flowers. The bacteria are also spread by splashing rain to flower buds, blooms, leaves and new shoots. Extended periods of warm (75-81oF), cloudy, humid weather during bloom are excellent for infection. Hail, frost, high winds or other weather related events or situations that create wounds will increase chances of infection. Severe pruning and excessive fertilization, which promote the rapid growth of succulent tissue, will also increase the vulnerability to fire blight.

Damage: Fire blight can be quite devastating on susceptible plants ranging from death of young plants to loss of entire limbs. On ornamental pears, certain cultivars can be severely disfigured by repeated infections. Damage due to fire blight on less susceptible cultivars maybe limited to scattered leaf browing and branch tip dieback.

Integrated Management Strategies:
Pruning diseased wood will limit the spread of the bacteria. During an extended dry period, but preferably in late winter during cold, dry weather, prune out all diseased wood 12 to 15 inches (if pruning during the growing season or 6 to 8 inches if pruning during the winter) below the edge of the canker. To avoid spreading the bacteria, pruning tools need to be disinfected with a 10% solution of household bleach after each cut. Clean up dead twigs and any mummified fruit on the ground that may harbor the bacteria. Follow pruning recommendations in MU Guide G6020.

Minimize succulent vegetative growth. Avoid fertilizing in the spring, which can cause succulent growth. If plant vigor is lacking, fertilize lightly in the fall. Avoid excessive pruning, which can also cause lush growth but do remove suckers at the base of the trees and waterspouts, which arise from the trunk or branches.

Replace diseased plants with resistant cultivars if the current plants are repeatedly and severely infected with fire blight.Resistant varieties are available except among edible pears. (See resistant varieties.)

Chemical sprays are not often very successful in managing the disease in the home landscape because timing is extremely critical for good control and therefore generally not recommended for home use. It is better to manage the disease with resistant cultivars and sanitation. For commercial applications and orchards, dormant copper sprays and streptomycin sprays at bloom and weekly there after are used. Repeated use of an antibiotic may result in the development of resistant strains of E. amylovora.

Photo Shepard's-crooking due to fire blight Figure 1. Shepard's-crook symptom, leaf blackening and canker caused by fire blight.

Photo tip dieback on flowering pear cultivar 'Capital' due to fire blight. Figure 2. Tip dieback on flowering pear cultivar 'Capital' due to fire blight. Drooping branches and blackened leaves are often diagnostic for fire blight.

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Email: plantclinic@missouri.edu

Cause:	The bacterium, Erwinia amylovora
Primary Hosts In Missouri:	Pear, apple, crabapple, pyracantha, cotoneaster, Callery Pears (Flowering ornamental pear)and other members of the rose family
Symptoms / Diagnosis:	The severity of the symptoms are dependent upon the cultivar and weather conditions at the time of infection, but symptoms typically include rapid death of shoot tips in spring. Symptoms typically include branch tip dieback. Affected branches turn black as if scorched by fire and are bent over in the diagnostic shepard's-crook (Figure 1). Brown to blacken, slightly sunken cankers form on the stems. The cankers are typically smooth, but cracks occur on the margins of the canker. The sapwood underneath the canker is streaked or uniformly blackened. In contrast freeze injured tissue does not show this streaking or blackening. Infections usually begin in the blossoms and cause the tissue to become water soaked, shrivel and quickly turn brown. Infection progresses into the peduncle, flower spurs and into the twig. Blighted peduncles, immature fruit and spurs also shrivel and turn almost black. Spurs and mummified fruit can remain attached to the tree for months. In some less susceptible cultivars the damage may be limited to only the flowers or cause scattered leaf blackening . In highly susceptible cultivars the bacteria progress into the twigs to cause significant dieback (Figure 2). Symptoms are typically reported to be more severe in older rather than younger trees. Because freeze injury does resemble fire blight injury it is not safe to assume that all tip dieback is related to fire blight. A laboratory diagnosis involves the observation of bacteria and culture from the diseased tissue for positive confirmation.
*Life Cyle:*	The bacteria overwinter in tissues surrounding twig and branch cankers. During wet, humid weather in early spring, the bacteria ooze from these cankers. This is attractive to insects, particularly honeybees and they spread the bacteria within the tree as well as to others as they visit flowers. The bacteria are also spread by splashing rain to flower buds, blooms, leaves and new shoots. Extended periods of warm (75-81oF), cloudy, humid weather during bloom are excellent for infection. Hail, frost, high winds or other weather related events or situations that create wounds will increase chances of infection. Severe pruning and excessive fertilization, which promote the rapid growth of succulent tissue, will also increase the vulnerability to fire blight.
*Damage:*	Fire blight can be quite devastating on susceptible plants ranging from death of young plants to loss of entire limbs. On ornamental pears, certain cultivars can be severely disfigured by repeated infections. Damage due to fire blight on less susceptible cultivars maybe limited to scattered leaf browing and branch tip dieback.
Integrated Management Strategies:	Pruning diseased wood will limit the spread of the bacteria. During an extended dry period, but preferably in late winter during cold, dry weather, prune out all diseased wood 12 to 15 inches (if pruning during the growing season or 6 to 8 inches if pruning during the winter) below the edge of the canker. To avoid spreading the bacteria, pruning tools need to be disinfected with a 10% solution of household bleach after each cut. Clean up dead twigs and any mummified fruit on the ground that may harbor the bacteria. Follow pruning recommendations in MU Guide G6020. Minimize succulent vegetative growth. Avoid fertilizing in the spring, which can cause succulent growth. If plant vigor is lacking, fertilize lightly in the fall. Avoid excessive pruning, which can also cause lush growth but do remove suckers at the base of the trees and waterspouts, which arise from the trunk or branches. Replace diseased plants with resistant cultivars if the current plants are repeatedly and severely infected with fire blight.Resistant varieties are available except among edible pears. (See resistant varieties.) Chemical sprays are not often very successful in managing the disease in the home landscape because timing is extremely critical for good control and therefore generally not recommended for home use. It is better to manage the disease with resistant cultivars and sanitation. For commercial applications and orchards, dormant copper sprays and streptomycin sprays at bloom and weekly there after are used. Repeated use of an antibiotic may result in the development of resistant strains of E. amylovora.

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	Email: plantclinic@missouri.edu