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Need to know:
- Affected leaves will blight and turn black and affected shoots will curl.
- Bacterial ooze is transmitted by insects, wind, and splashing rain to infect healthy plants.
- Infected branches should be pruned to reduce impact.
Overview of fire blight
Fire blight is a common springtime disease of apple, pear, and related species, including crabapple, hawthorn.
Symptoms of fire blight
Leaves on affected branches wilt and turn black, appearing as if scorched by fire. The most characteristic symptom is the curling of affected shoots into curved "shepherd's crooks". Cankers (areas of sunken or discolored bark) may develop on limbs, and the blighted shoots may produce sticky ooze (signs) in wet weather.
Signs of fire blight
Cankers and the blighted shoots may produce sticky ooze (signs) in wet weather. During wet weather, bacteria may also ooze and later dry to a white residue in shoot, flower or fruit.
Disease cycle of fire blight
Fire blight is caused by a bacterium Erwinia amylovora. The bacterium survives the winter in cankers on infected branches. In the springtime, sticky bacterial ooze formed at the edges of the cankers is carried to healthy plants by insects, wind, and splashing rain. Healthy plants may become infected through blossoms or wounds.
Type of Sample Needed for Diagnosis and Confirmation
The Iowa State University Plant & Insect Diagnostic Clinic can help you investigate and confirm if your plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each state's diagnostic laboratory for U.S. residents. If your sample is from outside of Iowa, please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us.
Several management tactics can help reduce the impact of fire blight. Sanitation is most important, and infected branches should be pruned out of the tree. It is best to prune when the plant and bacterium are dormant, during the winter. Infected branches should be pruned at least 12 inches below the area that looks diseased, to remove all of the bacteria.
Resistant varieties should be planted whenever possible. Although they are not completely immune to fire blight, resistant varieties are less impacted by the disease than are other varieties. Pears tend to be more susceptible than apples.
Commercial growers can use bactericidal sprays, such as copper sulfate or streptomycin, during the bloom period. However, bactericides are ineffective without proper sanitation. Recommended fungicides for commercial production can be found at the most up to date Fruit Production Pest Management Guide.
Fungicide applications may be avoided by following good Integrated Pest Management practices like those listed in this encyclopedia article. Often, the only preventative application is effective to manage plant diseases. If the problem requires a fungicide, state law requires the user to read and follow all labels accordingly. For more information, read Proper fungicide use.
Dr. Lina Rodriguez-Salamanca is a diagnostician and extension plant pathologist with the Iowa State University Plant and Insect Diagnostic Clinic (clinic.ipm.iastate.edu), a member of the National Plant Diagnostic Network (NPDN, ...
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