Fire Blight: How to Identify and Treat It

Fire blight is a bacterial disease that makes branch tips on pears, apples, crabapples and related shrubs look scorched, with blackened leaves that cling to the twig and shoot tips that bend over into a shepherd’s crook. It cannot be cured with a single spray. The working plan for homeowners is three-part: prune out infected wood well below the visible damage with disinfected tools, use copper sprays before bud break and protective sprays during bloom when the weather favors infection, and stop pushing soft, fast growth with heavy nitrogen and hard pruning. Choosing resistant varieties is the long-term fix.

In this guide

1. What Causes Fire Blight
2. Plants Fire Blight Attacks
3. How to Identify Fire Blight
4. How to Prune Out Fire Blight
5. Spraying: What Works and When
6. Cultural Practices That Reduce Fire Blight
7. Choosing Resistant Varieties
8. A Year-Round Fire Blight Calendar
9. When to Call a Professional
10. Frequently Asked Questions

What Causes Fire Blight

Fire blight is caused by the bacterium Erwinia amylovora. It overwinters in cankers on infected branches. In spring, as temperatures warm and trees bloom, the cankers ooze bacteria in sticky droplets. Rain splash, insects and pollinating bees carry the bacteria to open flowers, which are the main entry point. From the blossoms the infection moves down into twigs and branches, and new shoots can be infected through wounds from hail, wind or pruning.

Infection risk is highest during bloom when temperatures are warm, roughly in the mid-60s to mid-80s °F, and there is rain, heavy dew or high humidity. A cool, dry bloom season can pass with little disease, while a warm, wet one can cause widespread damage in a few weeks.

Plants Fire Blight Attacks

Fire blight affects members of the rose family, especially those in the pome-fruit group:

• Pears, including European and Asian pears. Many European pears, such as Bartlett, are highly susceptible.
• Ornamental Callery pears, though resistance varies by cultivar.
• Apples and crabapples.
• Quince and flowering quince.
• Hawthorn, pyracantha (firethorn), cotoneaster, mountain ash and serviceberry.

For care of the most common hosts, our guides on how to grow a pear tree and how to grow an apple tree cover site selection and feeding. For a broader look at diagnosing and caring for woody plants, see our trees and shrubs guide.

How to Identify Fire Blight

Stage	What you see	When
Blossom blight	Flowers wilt, turn brown or black and stay on the spur	Bloom and shortly after
Shoot blight	Young shoots wilt and bend into a shepherd’s crook; leaves blacken along the midrib and stay attached	Late spring to summer
Ooze	Amber or milky droplets on blossoms, shoots or bark, sometimes in strands	Warm, humid weather
Fruit blight	Small fruit shrivel, darken and mummify on the tree	Early summer
Cankers	Sunken, dark, cracked bark at the base of infected shoots or on limbs	Visible from summer through winter

The overall look gives the disease its name: affected branches look as if they have been scorched by fire. Pear leaves turn black, apple leaves typically brown. Dead leaves cling to the branch through winter rather than dropping, which helps you spot infections after leaf drop.

What fire blight is not

• Leaf scorch from drought or heat browns leaf edges but does not cause the shepherd’s crook or ooze.
• Frost damage kills blossoms but does not move down into twigs over the following weeks.
• Apple scab produces olive-green to black spots on leaves and fruit, not whole scorched shoots. Our guide on why apple leaves get spotted covers scab and other leaf spots.
• Borers and other insects can cause wilting, but you will usually find holes or frass.

How to Prune Out Fire Blight

Pruning is the most important home treatment. The goal is to remove infected wood before the bacteria move further into the tree.

In the growing season

1. Wait for dry weather. Pruning in rain or humid conditions spreads bacteria.
2. Find the lowest point of visible damage on the branch, including any discolored bark.
3. Cut 8 to 12 inches below that point into healthy wood. On highly susceptible pears, go toward the longer end.
4. Cut back to a branch junction or lateral where possible, rather than leaving a stub.
5. Disinfect pruners between every cut with 70 percent rubbing alcohol or a 10 percent household bleach solution. Bleach corrodes tools, so rinse and oil them afterward.
6. Bag and remove cuttings from the site. Do not compost them.

Some orchard specialists use the ugly stub method: cutting well into older wood and leaving a 4- to 6-inch stub that is removed cleanly in winter. This limits fresh wounds near active infections.

In winter

Dormant season is the best time to remove cankers on larger limbs, since bacteria are inactive. Look for sunken, cracked, discolored bark, often with dead leaves still attached above it. Cut at least 4 inches, and ideally more, below the canker margin, or remove the whole limb if the canker girdles it. Winter pruning also lets you thin crowded canopies to improve airflow. Our guide on how to prune fruit trees covers general structure and timing.

Spraying: What Works and When

No spray cures existing infections. Sprays protect healthy tissue, mainly blossoms, during high-risk periods. Always read the label: products, rates and legal uses vary by state and by crop.

Copper at green tip

A fixed copper spray applied when buds are just breaking, at silver tip to green tip, helps reduce the bacteria on bark and around cankers before bloom. Copper applied after bloom can russet or mark apple and pear fruit, so most labels limit later applications or call for low rates. If you are deciding between copper and other options for fruit trees in general, our guide on copper vs sulfur fungicide compares them. You can find fixed copper products labeled for fire blight through an Amazon search for copper fungicide.

During bloom

Open blossoms are where most infections start, so bloom-time protection matters most in warm, wet springs. Options include:

• Biological products based on beneficial bacteria such as Bacillus subtilis or Bacillus amyloliquefaciens, which colonize flowers and compete with the pathogen. These suit home gardeners and organic growers. Look for Bacillus subtilis biofungicides labeled for fire blight.
• Antibiotics such as streptomycin, used by commercial orchards. Availability to homeowners is limited, and resistance has developed in some regions, so check with your local extension office before relying on it.
• Some low-rate copper formulations are labeled for bloom use, but watch for fruit russeting.

Bloom sprays are typically repeated every few days through bloom when weather is warm and wet, since new flowers open daily. Spraying in a cool, dry bloom period usually adds little.

After bloom

Spraying after symptoms appear rarely stops the spread. Focus on pruning and on preventing new infections from hail or wind damage. After a hail storm during the growing season, some growers apply a protective spray within a day to protect fresh wounds.

Cultural Practices That Reduce Fire Blight

• Go easy on nitrogen. Heavy nitrogen fertilizer and lawn fertilizer applied near trees push soft, rapid shoot growth that is highly susceptible. Feed based on soil tests and growth, not by habit.
• Avoid heavy pruning. Hard cuts trigger vigorous water sprouts and suckers, which are easy targets. Prune moderately every year instead of severely every few years.
• Remove water sprouts and root suckers during dry weather.
• Remove late, secondary blossoms that open after the main bloom. These rattail blooms are frequently infected.
• Control sucking insects such as aphids and leafhoppers on susceptible trees, since they create wounds and spread bacteria.
• Avoid overhead irrigation on fruit trees, which keeps bark and flowers wet.
• Clean up nearby wild or abandoned hosts, such as neglected pears or hawthorns, which can serve as a source of bacteria.

Choosing Resistant Varieties

No variety is immune, but resistance makes a dramatic difference. When planting new trees:

• Pears: varieties such as Kieffer, Moonglow, Magness and Seckel are generally more resistant than Bartlett, Bosc and many other European pears. Some Asian pears are also highly susceptible.
• Apples: Liberty, Enterprise and several other disease-resistant cultivars are less susceptible than Gala, Fuji, Jonathan and Granny Smith. Rootstock matters too. Some common dwarfing rootstocks are very susceptible, which can lead to rootstock infections that kill the tree.
• Ornamentals: check the nursery tag or your extension service for fire blight ratings on crabapples, pyracantha and cotoneaster.

If you are planning a new orchard planting, our guide on how to grow a crabapple tree covers disease-resistant ornamental choices.

A Year-Round Fire Blight Calendar

• Winter (dormant): walk every susceptible tree, mark and remove cankers and blighted twigs with clinging dead leaves, and thin crowded growth. Clean up any mummified fruit.
• Late winter to early spring (silver tip to green tip): apply fixed copper according to the label.
• Bloom: watch the forecast. When days are warm and rain or heavy dew is expected, apply a bloom-labeled protective product and repeat at label intervals until petal fall.
• Late spring to early summer: scout weekly for wilting shoot tips and blackened blossoms. Prune out strikes promptly in dry weather, disinfecting tools between cuts.
• Summer: remove water sprouts and late rattail blossoms. Hold back on nitrogen and skip heavy summer pruning.
• Fall: rake up and remove fallen fruit and leaves around trees, and note which trees were hit hardest so you can plan winter pruning or replacement.

When to Call a Professional

Large trees with cankers on the trunk or main scaffold limbs, or trees near power lines, are best handled by a certified arborist. Removing large limbs safely, and judging whether a tree can be saved, takes experience. If most of the canopy is infected or the trunk is girdled by a canker, replacement with a resistant variety is often the better choice. For typical prices, see our guide to fruit tree pruning cost.