Fire blight on pear — symptoms and treatment

Severity: high

What is Fire blight

Fire blight is caused by the bacterium Erwinia amylovora. It is the most devastating bacterial disease of pome fruit trees, and its high severity rating is earned: unlike leaf diseases that cost you a season, fire blight moves from blossoms into shoots, from shoots into limbs, and from limbs into the trunk and rootstock, where it can kill a mature pear outright.

Symptoms

The first phase is at bloom. Infected blossoms darken, wilt and turn black, and the infection runs down the flower stalk into the spur and shoot. On new shoots comes the diagnostic sign: the growing tip wilts and bends over sharply into a hook — the shepherd's crook — while the leaves along it blacken but do not drop. In humid weather, droplets of sticky amber to milky bacterial ooze appear on shoots, fruitlets and cankers. In older wood the infection forms bark cankers, sunken and darkened at the margin between dead and living tissue. Cankers reaching the trunk or rootstock kill the tree.

• Early signs: blackened, wilted blossoms; a wilting shoot tip beginning to bend
• Advanced signs: shepherd's crook shoots with clinging blackened leaves, ooze droplets, sunken bark cankers
• Confusable with: frost damage on blossoms early on — the crook, the ooze and the spread into wood confirm fire blight

Causes and conditions

The bacterium overwinters at the margins of bark cankers and becomes active as the tree breaks dormancy. In warm, humid spring weather it multiplies and oozes out, then travels to open blossoms on pollinating insects, other insects, rain splash and wind-driven rain. Blossoms are the main entry point, which is why bloom is the critical window and why a warm, wet bloom produces a severe year. It also enters through wounds — hail, storm damage, insect punctures and pruning cuts made in the wrong weather. Soft, succulent growth is the most vulnerable tissue, so heavy nitrogen and hard pruning make trees more prone.

Treatment

Pruning infected wood — cultural

Timing: during dry weather. Prune infected branches 30-40 cm below visible symptoms. Sterilize tools between cuts with 70% alcohol. Cutting well below the visible margin matters because the bacterium runs ahead of the symptoms inside the wood — a cut at the edge of the blackening leaves the infection in the tree. Take the removed wood off the site and destroy it.

Streptomycin (where permitted) — chemical

Timing: during bloom. Apply during bloom when temperatures exceed 18°C. Copper sprays during dormancy. Check local regulations. Bloom sprays are protective: they defend open flowers during the infection window and do nothing for wood already infected. Pre-harvest interval: 50 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Cut out cankers during dormancy — they are the overwintering source that starts each spring
• Prune only in dry weather and sterilise tools between every cut
• Avoid heavy nitrogen and hard pruning that force soft, succulent shoots
• Plant less susceptible pear varieties and rootstocks where available
• Remove blighted shoots promptly, before ooze spreads the bacterium further

Frequently asked questions

Can I save a tree with fire blight? Often yes, if you catch it while it is still in shoots and small branches: cut well below the visible symptoms in dry weather. Once cankers reach the trunk or rootstock the tree is usually lost, and removing it protects neighbouring trees.

Is it contagious to other trees? Yes — it spreads readily to other pears, apples, quinces and related pome fruit, carried by insects and rain. Stone fruit such as plums and peaches are not affected.

When should I treat? At bloom, when blossoms are open and vulnerable and protective sprays have value. Pruning is separate: do it whenever you find infected wood, but only in dry conditions.