Fire Blight Symptoms Now Visible

Fire blight is the most important disease of apple and pear in Kentucky. Symptoms have begun to appear throughout the Commonwealth; however, initial infections occurred at bloom. The pathogen survives winter in dead, dying, and diseased wood and in cankers. Removal of these pathogen sources can reduce spread of fire blight and should be completed in late winter while the pathogen is dormant.

Fire Blight Facts

  • Early symptoms include wilt of flower clusters and blossom death (Figure 1). Disease spreads to shoots or branches where tips wilt and rapidly die (blight) to form a characteristic ‘shepherd’s crook’ (Figure 2). Dark brown, sunken cankers (stem lesions) develop and expand to girdle branches, resulting in branch death (Figure 3).
  • Potential hosts include apples, pears, and several landscape woody ornamentals in the rose family.
  • Primary infection occurs at bloom and may continue through petal fall or until shoot elongation ends.
  • Rainy conditions, periods of high humidity, and temperatures between 65° to 70°F favor disease development.
  • Caused by the bacterium Erwinia amylovora.
  • Bacterial cells overwinter in dead, dying, and diseased wood.
Figure 1: Apple flower clusters infected with fire blight. (Photo: Nicole Ward Gauthier, UK)

Figure 1: Apple flower clusters infected with fire blight. (Photo: Nicole Ward Gauthier, UK)

Figure 2: Rapid shoot death from fire blight may result in a ‘shepherd’s crook’ appearance. (Photo: Nicole Ward Gauthier, UK)

Figure 2: Rapid shoot death from fire blight may result in a ‘shepherd’s crook’ appearance. (Photo: Nicole Ward Gauthier, UK)

Figure 3: Dark brown, shrunken cankers develop and expand to girdle branches. (Photo: Nicole Ward Gauthier, UK)

Figure 3: Dark brown, shrunken cankers develop and expand to girdle branches. (Photo: Nicole Ward Gauthier, UK)

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Management Options

  • Select varieties that are tolerant or resistant to fire blight.
  • Maintain plant health with proper nutrition and irrigation practices.
  • Prune to increase air flow through the plant canopy.
  • Remove infected plant tissues during winter when plants and pathogens are dormant. Do not prune when trees are wet. Burn, bury, or otherwise dispose of diseased material.
  • Bactericides should be applied preventatively. Once infection occurs, sprays are not effective. Homeowners can apply copper during dormancy to reduce overwintering inoculum. Additional bactericides available for commercial growers are presented in the Midwest Fruit Pest Management Guide (ID-232). Always follow label directions when utilizing bactericides.
  • Fire blight risk throughout the season can be determined by disease development models. Visit the UK Ag Weather Center site for additional information.

Additional Information

  • Backyard Apple Disease Management Using Cultural Practices (with Low Spray, No Spray & Organic Options) (PPFS-FR-T-21)
  • Commercial Midwest Fruit Pest Management Guide (ID-232)
  • Disease and Insect Control Programs for Homegrown Fruit in Kentucky including Organic Alternatives (ID-21)
  • Fire Blight (PPFS-FR-T-12)
  • Fruit, Orchard, and Vineyard Sanitation (PPFS-GEN-05)
  • Simplified Backyard Apple Spray Guides (PPFS-FR-T-18)

 

By Kim Leonberger, Extension Associate and Nicole Ward Gauthier, Extension Specialist

 

 

Posted in Fruit