Fire blight on quince — symptoms and treatment

Severity: high

What is Fire blight

Fire blight on quince is caused by Erwinia amylovora, and quince is highly susceptible to it — more so than most fruit trees it shares an orchard with. The name describes the look: affected blossoms and shoots blacken as though scorched. It is a bacterial disease, so nothing cures it once it is inside the wood, and it does not stop at the shoot it started on. It moves down into branches and the trunk, killing as it goes, and it can take a mature tree. Hence the high severity, and why the response has to be immediate and drastic.

Symptoms

Infection normally starts at the blossoms, which blacken and die but stay hanging on the tree instead of dropping. From there it moves into the shoot, and the growing tip wilts and bends into a tight hook — the shepherd's crook, the most reliable diagnostic sign this disease offers. In warm humid weather the infected tissue exudes a bacterial ooze, droplets that dry into streaks on the bark; this ooze is not just a symptom but the source of further spread. As the bacteria work back into older wood, cankers form in the bark — sunken, darkened areas with a distinct margin — and branches die rapidly beyond them.

• Early: blackened blossoms and shoot tips; blossoms hanging on the tree.
• Diagnostic: shepherd's crook — the shoot tip wilted and hooked over.
• Advanced: bacterial ooze; bark cankers; rapid branch death.
• Confusable with: frost damage on blossom — but frost does not produce ooze, cankers or the crook.

Causes and conditions

The bacteria overwinter in bark cankers on the tree. In spring they multiply and ooze out, and insects — attracted to the ooze and working the open blossoms — carry them straight to the flowers, which is why bloom is the critical infection window. Rain splash spreads them further, and they enter through blossoms, wounds and pruning cuts. Warm, humid weather during bloom turns a quiet canker into an orchard-wide outbreak. Pruning tools spread the disease efficiently from cut to cut, and pruning in wet weather spreads it further still.

Treatment

Aggressive pruning — cultural

Timing: during dry weather. Cut infected branches 40+ cm below visible symptoms. Sterilize tools between each cut. Burn infected wood. All three parts are non-negotiable. The bacteria are already ahead of what you can see, which is why the cut goes 40+ cm below the visible symptom — cut at the edge of the damage and you leave the infection in the tree. Sterilise between every cut, or the tools carry it to healthy wood. Burn what you remove.

Copper spray — chemical

Timing: dormancy and bloom. Apply copper at dormancy. During bloom, use streptomycin (where permitted) or biological alternatives. Copper at dormancy knocks back the overwintering bacteria before they start oozing; bloom is when blossoms are open and vulnerable. Pre-harvest interval: 21 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Inspect for and cut out cankers during dormancy — they are where the outbreak comes from each spring.
• Prune only in dry weather, and sterilise tools between every cut.
• Avoid unnecessary wounds during the growing season; every wound is an entry point.
• Burn or destroy all infected wood rather than leaving prunings near the tree.
• Watch the tree through bloom, when infection takes hold, and act on the first blackened blossoms.

Frequently asked questions

Can I save a tree with fire blight? Often yes, if you act fast and cut hard — 40+ cm below the visible symptoms, sterilising between cuts. Trees are lost by cutting timidly at the edge of the damage and leaving the bacteria in the wood.

Why must I cut so far below the damage? Because the bacteria have already spread beyond the part you can see. The visible symptom marks where the tissue has died, not where the infection ends.

Is it contagious to my other fruit trees? Yes. It spreads to other trees in the same family, carried by insects and rain splash from bacterial ooze, and on unsterilised pruning tools. Quince is especially susceptible.