Fire Blight

Erwinia amylovora

Fire Blight is a destructive bacterial disease of apple, pear, crabapple, quince, loquat, pyracantha, and other rosaceous hosts caused by Erwinia amylovora. Blossoms and young shoots blacken rapidly, shoot tips bend into a shepherd’s crook, and leaves remain attached as if scorched by fire. Amber, milky, or reddish bacterial ooze may emerge from fresh cankers during humid weather. Warm bloom periods, rain, hail, vigorous succulent growth, and insect or pruning wounds increase infection. In North Florida, pear, loquat, and susceptible ornamentals can experience severe outbreaks during warm wet bloom. Strikes can move into limbs and rootstocks, killing young trees. Accurate timing matters because blossom protection and removal of dormant cankers are preventive; spraying after shoots are already black does not restore infected tissue.

Identification

Inspect blossoms, shoot tips, fruit spurs, and branch crotches. Fresh infections often show a sharp transition between healthy green tissue and water-soaked or blackened growth. Peel bark at a canker margin to look for reddish-brown streaking. Collect entire shoot tips or limb sections containing several inches of healthy tissue below the active margin. Keep samples cool and dry. Laboratory confirmation may use bacterial isolation, serology, or PCR. Frost can blacken blossoms uniformly after a weather event; blossom blast caused by Pseudomonas may look similar; fungal cankers often develop slower and may form fruiting bodies; herbicide injury lacks bacterial ooze and can follow application patterns.

Symptoms / Signs

Blossoms wilt, turn brown or black, and remain attached. Young shoots develop a hooked tip and blackened leaves that cling to the stem. Cankers are sunken, dark, and sometimes cracked at their margins. During moist weather, droplets or threads of bacterial ooze can form. Fruitlets shrivel into dark mummies. On pear, foliage often turns nearly black; apple symptoms may be browner. Rootstock infection can cause reddish streaking, rapid decline, and death below otherwise limited canopy symptoms. Not every black shoot is fire blight, particularly after freeze or mechanical damage.

Life Cycle / Process

The bacterium overwinters in living tissue at canker margins. During warm humid spring weather it multiplies and oozes to the surface. Rain, insects, wind, and tools carry cells to blossoms, where they multiply on stigmas and enter through nectarthodes. Shoot infection occurs through wounds from hail, wind, insects, pruning, or rapid growth. Bacteria move internally through succulent tissue and can reach limbs, trunks, or rootstocks. Warm temperatures around bloom and frequent wetting create explosive disease cycles. Excess nitrogen and aggressive pruning increase susceptible growth.

Prevention

Select resistant cultivars and rootstocks where appropriate. Avoid excessive nitrogen and unnecessary dormant or summer pruning that stimulates succulent shoots. Remove known cankers during dry dormant weather, cutting well below visible margins. Disinfect tools between trees or cuts when active infection is present. Monitor bloom-stage risk models and weather advisories. Apply blossom-protection products only according to crop-specific timing, resistance stewardship, and labels. Manage insect and hail wounds where practical. Do not use highly susceptible rosaceous ornamentals as unmanaged reservoirs near commercial orchards.

Management / Control

During active outbreaks, prune strikes only in dry weather when doing so can be completed without spreading bacteria; cut well below visible symptoms into healthy wood. In high-risk warm wet periods, marking strikes for later removal may be safer than repeated wet pruning. Destroy removed branches away from susceptible hosts. Review nitrogen and irrigation practices. Antibiotics, copper, and biological products have narrow preventive windows and crop-specific restrictions; resistance to streptomycin occurs in some regions. Rootstock or trunk infection may require removal of the tree. Continue scouting after storms and through vigorous shoot growth.

Procedure Steps

1. Photograph blossom clusters, shepherd’s-crook shoots, cankers, and any ooze. 2. Record host, cultivar, rootstock, bloom date, hail, pruning, nitrogen, and recent temperatures. 3. Collect complete fresh strikes with healthy tissue below the margin. 4. Compare with frost, Pseudomonas blossom blast, fungal cankers, and herbicide injury. 5. Submit samples when the host or symptoms are atypical. 6. Prune only under dry conditions using host-appropriate distances below symptoms. 7. Clean tools and remove cut material from the block. 8. Use current risk models and labels for future blossom protection.

Safety Notes

Pruning ladders, pole saws, and dead limbs create physical hazards; use qualified personnel for large trees. Wear label-required protection for copper, antibiotics, and biological products. Agricultural antibiotics are not general garden remedies and must be legal for the crop and use. Prevent spray drift during bloom and protect pollinators according to labels. Do not burn prunings where fire restrictions apply.