Disease of the Month - Fireblight

  Hort Snacks - May 2018
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 Causal Organism(s): Erwinia amylovora

Crops Affected: Wide host range – all plants with the Rosaceae (apples, crabapple, pears, mountain ash, cherries, Saskatoon berries, hawthorn, cotoneaster, etc.), caneberries (raspberry, etc.)

Disease Cycle:

  • Bacterial pathogen
  • Overwinters on the edges of branch cankers
  • Disseminated by crawling or flying insects, including pollinators as they move from blossom to blossom
  • Also spread through rain splash, wind, and physical transfer by pruning or other tools
  • Bacteria enter through natural plant openings (within flowers, vegetative growing points, etc.) or through wounds (mechanical, insect, etc.)
  • The pathogen multiplies rapidly, depending on weather, however it may remain in a epiphytic (not attacking) state for a period of time before starting to infect and cause typical symptoms
  • Plant parts and foliage develops a scorched (burned) appearance
  • Sudden wilting & browning of blossoms
  • Infected plant parts may become purplish black and water-soaked lesions may develop
  • Wilting of new shoots in characteristic “Shepherd’s Crook”
  • Raspberry canes may be girdled
  • Young fruit may turn brown or black
  • Infected raspberries do not mature, become brown, dry up,become very hard and remain on pedicel
  • Bacterial ooze may be seen during periods of high humidity
  • There is a strain specific to raspberries that will not infect apples
    • apple strain will affect raspberries

Saskatoon berry orchard - heavily infected with Fireblight
Fireblight on Saskatoon berry - note - scorched tissues
Photo submitted from Lloydminster area
Photo by Robert Spencer

Conditions Favouring Disease Development
  • Presence of bacteria from overwintering cankers on diseased plant material
  • Warm / moist / humid / rainy conditions favour infection
  • Prolonged host flowering due to cool, wet conditions
  • Succulent host tissue
  • Damaged tissue can allow entry of pathogen
  • Avoid succulent growth and injury to tissues
  • Pruning can take place either during dormant season or when disease is observed in season
    • Prune out infected shoots 25-45 cm below the lowest point of infection (woody plants – e.g. apple, crab, pear, etc.)
    • Prune out infected raspberry canes
  • Disinfect pruning equipment between cuts
  • There are essentially no chemical products registered for control of fire blight
  • 2 biological products are registered for suppression of fire blight in Saskatoon berries, caneberries & non-bearing apples (nursery stock)
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For more information about the content of this document, contact Robert Spencer.
This information published to the web on April 26, 2018.