| 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
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
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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
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
- 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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