Fire Blight
Erwinia amylovora
67 host plants
Last updated
Fire blight announces itself in spring through scorched, blackened shoots that look as though they've been burned; in some cases, an entire young tree collapses at the graft union without showing canopy symptoms first. On apple and pear, you'll notice wilted flowers and shoots with a distinctive shepherd's crook appearance, and close inspection reveals cankers near the base of trunks that are dark, water-soaked, and purplish. The bacterium Erwinia amylovora enters through open flowers (which remain vulnerable for 1 to 3 days), fresh wounds, and growing shoot tips. Temperature above 65°F coupled with rain or high humidity during bloom creates the infection window.
Fire blight can kill young trees outright and severely damage bearing orchards, making prevention and rapid response your critical management tools. Choose resistant rootstocks (Geneva series G. 11, 30, 41, 65, and others) and resistant cultivars when establishing new plantings. At the first sign of blight, remove all infected material by cutting well into healthy wood, sterilizing tools in a 10% bleach solution between every cut, and never combine pruning and blight removal in the same season. When conditions favor infection, copper and other registered bactericides applied at bloom help reduce the risk, and some growth regulators like Apogee on apple show promise for early-season applications.
Quick Reference
Management
Bloom period through 3 weeks post-petal fall, when temperatures exceed 65°F and moisture is present. Open flowers are the primary infection court; viable for 1-3 days.
Temperature ≥65°F in 24-hour period plus trace of rain or humidity >65% (PNW Disease Handbook). Bacteria enter through open flowers (viable 1–3 days), shoots, wounds.
Cultural Controls
- Remove and destroy all blighted wood promptly. Cut at least 8-12 inches below visible symptoms into healthy wood.
- Sterilize tools between every cut with 70% ethanol, 70% isopropanol, or 10% bleach solution.
- Do not combine structural pruning and blight cutting in the same pass.
- Remove holdover cankers during dormant season to reduce inoculum sources.
- Avoid excessive nitrogen fertilization; vigorous succulent growth is more susceptible.
- Resistant rootstocks for apple: Geneva series (G.11, G.30, G.41, G.65, G.202, G.210, G.214, G.222, G.814, G.890, G.935, G.969) and Budagovsky 9, 10. Susceptible rootstocks: M.9, M.26.
Common and serious on pear and apple in the Puget Sound region. Cool wet springs delay bloom but create extended infection windows when warm spells coincide with rain during open flowers. Maritime humidity regularly exceeds the 65% threshold for infection. Ornamental Rosaceae (crabapple, hawthorn, mountain ash, pyracantha) are frequent landscape hosts. Fire blight causes more home orchard losses than any other bacterial disease in this region.