Fireblight

Causal Organism(s): Erwinia amylovora

Crops Affected: Wide host range – all plants with the Rosaceae (apples, crab apple, 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 an epiphytic (not attacking) state for a period of time before starting to infect and cause typical symptoms

Symptoms:

Apple-type plants:

• Plant parts and foliage develops a scorched (burned) appearance
• Sudden wilting & browning of blossoms
• Wilting of new shoots in characteristic “Shepherd’s Crook”
• Infected plant parts may become purplish black and water-soaked lesions may develop

Raspberries:

• 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
  • Note: apple strain will affect raspberries

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 – can be caused by excessive levels of nitrogen causing vigorous tender vegetative growth
• Damaged tissue can allow entry of pathogen

Management:

• 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
  • Using a 10 per cent solution of Lysol can effectively disinfect tools
• 2 biological products are registered for suppression of fire blight in Saskatoon berries, caneberries & non-bearing apples (nursery stock)
  • These must be applied PRIOR to infection, not after infection is observed
• There are essentially no chemical products registered for control of fire blight

Fireblight on pear tree – darkened / purplish areas on branch