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Larry A. Sagers Regional Horticultural Specialist Utah State University Extension Service Thanksgiving Point Office © All Rights Reserved

Fire blight is one of the most serious the bacterial diseases. It is extremely serious on pears and some varieties of apples. Fortunately ornamental pears are resistant but many varieties of crabapples are susceptible. Other plants that are susceptible to fire blight include hawthorns, pyracantha, photinia and cotoneaster.

According to the fire blight models, the risk of infection for much of northern Utah will likely be LOW tomorrow and Friday, unless blight was local last year.

If fire blight was local last year, or if you have a history of problems with this disease, then the risk of infection will be moderate. The rains predicted for this weekend will increase the risk of infection. Bactericides such as streptomycin (Fertilome fire blight spray) or copper are the best defenses against blossom infection.

Applications immediately before rain helps suppress fire blight bacterium.

Fire blight symptoms include scorched appearance of leaves, blossoms, and young terminal shoots. Blighted leaves remain attached to the tree through much of the dormant season.

Infected terminals exhibit a typical curling on the end, called a shepherd’s crook. A diagnostic symptom of fire blight infection is small droplets of bacterial ooze, light amber in color on infected leaves, flowers, and young infected terminals.

Pear trees are more susceptible to fire blight than apple. Infection of pear flowers or terminals may progress into larger branches and even into the trunk to kill the trees.

Fire blight was first observed in the late 1700’s in the North Eastern United States. It is caused by the bacterium Erwinia amylovora and infects many ornamental plants of the rose family.

It not only destroys the current season’s crop, but may also damage the structure of the tree and reduce subsequent production. Highly susceptible trees may be killed in a single season. Shoot tip infected with fire blight showing characteristic shepherds crook.

Rain disperses the ooze by splashing. Even if there are no cankers in the orchard, bacteria may still be present.

Bees and any other insects which visit flowers can spread bacteria to new infection sites. The tree is susceptible to infection until new growth stops.

Avoid practices that promotes excessive succulent growth. Overfertilization with nitrogen or applications late in the season cause too much new susceptible growth. Remove blighted blossoms and twigs as soon as they are evident. The best way to do this is to break them off by hand 8 - 12 inches below the obvious infection.

Pruners need not be sterilized between cuts when pruning during the dormant season. Soak pruners for 1 minute in a 10% solution (1 part bleach:9 parts water) of household bleach or good surface disinfectant between cuts when pruning out active fire blight in the summer. This preparation is effective but is corrosive to pruning tools.

Rinse, dry, and oil the tools several times during the pruning.

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