Fire blight on pears

Fire blight is a bacterial disease -- not fungal -- that makes pear branches die in a distinctive hook shape, as if the tips were scorched. It spreads through open blossoms during warm, wet spring weather, moving from flower to flower faster than most gardeners realize is possible. Pears are more.

—- title: "Fire blight on pears" slug: fire-blight-on-pears hub: problems category: "Disease-by-host" description: "Fire blight kills pear branches rapidly in warm spring weather. Identify the shepherd's crook, understand infection through flowers, and learn the pruning and management approach that slows a serious bacterial disease." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-

Fire blight is a bacterial disease — not fungal — that makes pear branches die in a distinctive hook shape, as if the tips were scorched. It spreads through open blossoms during warm, wet spring weather, moving from flower to flower faster than most gardeners realize is possible. Pears are more susceptible than apples; some European pear varieties have essentially no resistance and require intensive management in most of the eastern US.

I don't grow pears at my Long Island property, so this guide draws on Cornell Cooperative Extension, Penn State Extension, and Clemson HGIC research.

The pathogen

Fire blight is caused by the bacterium Erwinia amylovora. Per Cornell Cooperative Extension, this North American native infects the entire apple family (Rosaceae: pears, apples, quince, serviceberry, hawthorn, crabapple, mountain ash) and is considered one of the most destructive bacterial plant diseases in the world.

The bacterium overwinters in cankers on infected wood — dark, water-soaked areas at the margins of blighted tissue. In spring, bacteria ooze from these cankers and are carried by rain, insects, and wind to open flowers.

Identification

Shoot blight (shepherd's crook)

Per Penn State Extension, the most conspicuous symptom is the "shepherd's crook":

• Infected shoots die from the tip back, with the shoot tip bending into a distinctive hook or crook shape as the tissue dies but remains pliable before fully desiccating
• The hooked shoot retains brown, dried leaves that cling to the branch rather than dropping
• The progression is rapid — a shoot that appeared healthy Monday may show shepherd's crook by Friday in warm, humid weather

Blossom blight

Per Clemson HGIC, the disease cycle on pears typically begins with blossom blight:

• Open blossoms turn brown and collapse, sometimes with visible bacterial ooze in very humid conditions
• Blossom infection spreads through the pedicel into the spur and branch
• Rapid spread from blossom cluster to adjacent tissue occurs within days

Cankers

Per Cornell Cooperative Extension, fire blight cankers on larger branches appear as:

• Dark, water-soaked, sunken areas on the bark surface
• A distinct margin between infected and healthy tissue — healthy wood is green-white when the bark is cut away; infected wood has a streaked, reddish-brown to brown discoloration
• Cankers may girdle scaffold branches or the trunk in severe infections, killing large portions of the tree

Confirming bacterial ooze

In warm, humid weather, bacterial ooze — a sticky, amber-colored liquid containing billions of bacteria — may be visible on infected tissue surfaces or on cut surfaces. Per Penn State Extension, the combination of shepherd's crook, rapid progression, and amber ooze is strongly diagnostic for fire blight.

Conditions that favor disease

Per Cornell Cooperative Extension, fire blight is most severe when:

• Temperatures are 75–85°F (24–29°C) during bloom
• There is high humidity, rain, or dew during the bloom period
• Strong winds carrying bacteria-laden rain events coincide with open bloom
• High-nitrogen fertilization has produced excessive succulent shoot growth

The risk period is primarily during bloom — typically 7–14 days in the mid-Atlantic and Northeast. Per Penn State Extension, the Cougar Blight or Maryblyt forecast models, available through Cornell and Penn State, predict infection risk based on daily temperature and rainfall.

Pear susceptibility

Per NC State Extension, pears as a genus are highly susceptible to fire blight, more so than apples:

Highly susceptible: Bartlett (Williams), Bosc, Clapp's Favorite (avoid in high-pressure areas without intensive management)

Better resistance: Harrow Sweet, Harrow Delight, Moonglow, Seckel, Honeysweet — all show improved resistance in comparative trials

Asian pears (Pyrus pyrifolia): generally less susceptible than European pears; vary by cultivar

Per Penn State Extension, for home orchardists in the eastern US, resistant cultivar selection is the most practical management choice.

Management

Pruning infected wood

Per Clemson HGIC, pruning out infected wood is the primary management approach for existing infections. Critical guidelines:

• Cut at least 8–12 inches below the visible margin of infected (brown) wood into clearly healthy tissue
• Make cuts during dry weather — cutting infected tissue in rain or dew spreads bacteria
• Disinfect tools with 70% isopropyl alcohol or 10% bleach between every single cut — bacteria on contaminated tools cause at least as many new infections as the disease itself
• Do not compost infected prunings; dispose in the trash or burn

Per Cornell Cooperative Extension, some pathologists recommend cutting 12–18 inches below visible symptoms in severe infections — the bacterium extends farther into the tissue than visible discoloration suggests.

Bactericide applications at bloom

Per Penn State Extension, for susceptible cultivars, protective bactericide applications during bloom reduce blossom infection. Registered products include:

• Copper-based bactericides — apply at tight cluster, pink, full bloom, and petal fall; copper can cause russet on fruit if applied at or after full bloom, so timing is important
• Streptomycin — the most effective option; registered for home use in some states; concerns about resistance development in some regions have led some programs to emphasize copper alternatives. Check current registration in your state before purchase.

Applications must be timed to cover open blossom tissue, not applied before or after bloom.

Fertility management

Per Penn State Extension, excessive nitrogen fertilization produces the succulent, rapidly growing shoot tissue that is most susceptible to fire blight. Do not over-fertilize pears. A soil test-based modest nitrogen application is appropriate; avoid high-nitrogen products near pear trees.

What does not work

Per Cornell Cooperative Extension, standard fungicides have no effect on fire blight — it is a bacterial disease. Trunk injections of antibiotics have not shown reliable efficacy.

Common problems table

Frequently Asked Questions

How far below symptoms do I need to cut?

Per Penn State Extension, at least 8–12 inches below the lowest visible discoloration. In active infections during warm, humid conditions, the bacterium may have spread further than the discoloration shows. Cutting 12–18 inches below symptoms, while seemingly severe, is recommended in high-pressure situations.

Why does fire blight come back even after pruning?

Per Cornell Cooperative Extension, fire blight returns for two reasons: overwintering cankers on branches that were not removed or not cut far enough below infection, and new blossom infections each spring from external bacterial sources (insects, rain). Annual bactericide applications during bloom on susceptible cultivars are necessary to limit new infections.

Is pear fire blight contagious to my apple trees?

Per Clemson HGIC, yes. Erwinia amylovora infects both pears and apples. An infected pear is a source of bacteria that can spread to nearby apples via insects and rain.

Can fire blight kill my entire pear tree?

Per Penn State Extension, yes — severe fire blight that reaches the trunk or main scaffold branches can kill entire trees. Trees with rootstock that is susceptible to fire blight are at particular risk because the bacterium can reach the rootstock through pruning cuts or natural spread, and rootstock death kills the entire tree. Trees on fire blight-susceptible rootstocks (such as Malling-Merton 106) are more vulnerable than those on resistant rootstocks.

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Recommended gear: Best serviceberry cultivars — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.

Sources

1. Cornell Cooperative Extension — Fire Blight Management
2. Penn State Extension — Fire Blight
3. Clemson HGIC — Fire Blight
4. NC State Extension — Pear Variety Selection