What Is Fire Blight? (3 Ways To Prevent It)

If your apple or pear tree has oozing cankers, shriveled black flowers, dead leaves, or wilted shoots, you might have a problem with fire blight.

So, what is fire blight? Fire blight is a bacterial disease that affects apple trees, pear trees, and other members of the Rosaceae plant family. It can spread by splashing water or by insects (including honeybees) – more so in warm, humid conditions. Fire blight can destroy tree limbs or the entire tree in severe cases.

Although there is no way to cure fire blight, there are ways to prevent the infection and slow its spread in your plants.

In this article, we’ll talk about fire blight, including what it looks like and how it spreads. We’ll also talk about how to prevent fire blight and how to choose trees that resist its effects.

Let’s begin.

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What Is Fire Blight?

Fire blight is a disease that affects apple trees, pear trees, and other members of the Rosaceae family. It is contagious and can spread to other trees in your yard unless you take steps to prevent it.

Fire blight can destroy entire limbs on an infected tree. In extreme cases, it can destroy the infected plant completely.

Fire blight is a big problem for commercial apple and pear growers. This disease can damage many trees in an orchard, especially if they are close together.

It often leads to thousands of trees being removed to prevent the spread of the disease. In some years, 5 to 10% of orchards are affected.

Fire blight exists in Canada, several states in the U.S., and in other countries around the world.

What Causes Fire Blight?

Fire blight is caused by the bacteria Erwinia amylovora. It is most likely to affect pear trees, but it can also affect apples, crabapples, raspberries, quinces, and others.

What Does Fire Blight Look Like? (Fire Blight Symptoms)

Fire blight causes several telling symptoms you can look for to identify it on your plants:

• A light-tan colored, watery “ooze” flowing from cankers (dead bark patches that are black, grey or violet) on twigs, branches, or trunks. This ooze is sticky and sweet, attracting insects that will spread the disease.
• Dark streaks on branches or trunks (where the ooze flowed and was exposed to air).
• Shriveled flowers, shoots, or fruit in spring (fruit turns dark and dry, looking “mummified”).
• Wilted flowers (black on pear trees, brown on apple trees).
• Water soaked, dull, gray flowers with ooze droplets in high humidity.
• Wilted shoots that bend downward (causing a “hook” appearance).
• Dead black leaves and fruit that stay on the tree after death (making it look “burned”, hence the name).
• Pink, orange, or red streaks on infected wood under bark.
• Brown, dried out wood.

How Long Does Fire Blight Last?

Fire blight can last for months if it kills the tree fast, or it can last for years if the tree survives.

Can All Trees Get Fire Blight?

Not every tree can get fire blight. However, every plant in the Rosaceae family can get fire blight, including many trees. No member of the Rosaceae family is known to be totally resistant to fire blight.

Plants in the Rosaceae family include:

• Blackberry
• Raspberry
• Strawberry
• Almond
• Apple
• Apricot
• Cherry
• Pear
• Peach
• Quince
• Roses
• Loquat
• Cotoneaster
• Crataegus (Hawthorn)

Can A Tree Survive Fire Blight?

A tree can survive fire blight, possibly still producing edible fruit.

How Is Fire Blight Spread?

Fire blight bacteria survives winter inside cankers (dead bark patches) on twigs, branches, or trunks. When spring arrives, the bacteria become active and multiply inside some of the cankers.

A light tan liquid starts to run from these cankers. The bacteria in this liquid can spread by wind or splashing water from rainfall and irrigation (watering trees).

The disease can also spread by tools (for example, pruning shears that are not cleaned between cuts).

Birds and insects are attracted to the ooze that results from fire blight. As a result, they can also transmit this disease from one plant to another.

Infection is more likely on plants injured by wind, hail, or insect damage. Younger plants are also more prone to fire blight damage, since they grow faster than established trees.

Fire blight infection is also more likely under ideal conditions:

• Rainy and humid weather (humidity above 60%)
• Temperatures of 75 to 85 degrees Fahrenheit (24 to 29 degrees Celsius) during the day, and above 55 degrees Fahrenheit (13 degrees Celsius) at night
• After severe weather events (hail, heavy rain, strong wind gusts), since these cause damage to branches and bring splashing water, both of which open trees up to infection.
• In highly susceptible varieties, bacteria move into the trunk or roots, which will cause death.

Do Bees Spread Fire Blight?

Bees can spread fire blight. When the flowers on an infected tree are contaminated, honeybees can spread the bacteria that cause fire blight.

Flies, ants, and pollen wasps may also be attracted by infected flowers or ooze from infected branches, so they can also spread the disease.

Does Fire Blight Stay In The Soil?

Fire blight does not survive in the soil. The bacteria that cause fire blight need a host (apple tree, pear tree, or other Rosaceae family member) to survive.

The bacteria will overwinter inside an infected plant in the cankers that form, but not in the soil. The splashing water (from rain or irrigation) that spreads fire blight bacteria does so by moving the infected ooze from branches or flowers – not by moving soil.

Does Fire Blight Go Away On Its Own?

Fire blight does not go away on its own, since there is no cure for the disease. Fire blight will persist until it kills the tree, or as long as the tree lives if it survives.

The best way to deal with fire blight is to prevent it from occurring in the first place – and to prevent its spread if it does appear.

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Fire Blight Prevention

There are several steps you can take to prevent the spread of fire blight:

• Prune away diseased branches in late winter, when the tree and bacteria are dormant. Cut 8 to 12 inches (or more) below visible fire blight injury (cankers). Ideally, remove an infected branch at point of connection to the tree. Also, avoid pruning when fire blight spreads rapidly (see next point). Dip or spray the pruning tool with 10% bleach solution between each cut, waiting 1 minute to ensure sterilization (use multiple tools and alternate to speed things up).
• Prune sensibly and remove cover crops, weeds, or tall grass to prevent moisture and humidity near the tree trunk.
• Burn or bury infected branches or trees. Remove the stump to prevent the disease from spreading to other nearby plants.
• Avoid fertilizer (especially ones high in nitrogen) and pruning when temperatures are 75 to 85 degrees Fahrenheit (24 to 29 degrees Celsius) during the day, and above 55 degrees Fahrenheit (13 degrees Celsius) at night. Both fertilizer and pruning will speed up new growth, making plants more susceptible to fire blight. Find another time to fertilize and prune.
• Avoid watering trees while they are blooming, since most infections begin in the flowers.
• Use drip irrigation to water plants. This will avoid splashing from sprinklers/hoses that can spread fire blight bacteria.
• Choose fire blight resistant varieties.
• Use grafting with fire blight resistant rootstock. This will prevent tree death, but susceptible branches from the scion can still be infected and die. Be careful when grafting apple or pear trees, since the graft union is a potential infection site. Use clean tools to make cuts.

The table below gives you an idea of what temperatures are ideal for fire blight to spread and which temperatures it would be safest to prune.

You can learn more about fire blight here.

Fire Blight Resistant Varieties

One of the best ways to avoid fire blight is to choose trees with good resistance. Not only will this prevent the disease from getting a foothold, but it will slow the spread as well.

Trees that bloom later in the season (when temperatures are warmer) are more likely to get severe blight damage.

Fire Blight Resistant Apple Trees

Below are some apple tree varieties that show moderate to high resistance to fire blight – make sure they are hardy to your plant growing zone before purchase:

• Ace Delicious
• Arkansas Black
• Britemac
• Centurion
• David
• Evereste
• Gold Rush
• Gold Spur
• Honey Crisp
• Indian Summer
• Keepsake
• Melrose
• NovaEasyGro
• Ozark Gold
• Priscilla
• Radiant
• Santana
• Topaz
• Vanguard
• Yates

You can see a long list of apple trees and their fire blight resistance ratings from Cornell University.

Fire Blight Resistant Pear Trees

Below are some pear tree varieties that show moderate to high resistance to fire blight – make sure they are hardy to your plant growing zone before purchase:

• Bell
• Harrow Delight
• Honeysweet
• Kieffer
• LaConte
• Magness
• Maxine
• Moonglow
• Old Home
• Seckel
• Starking Delicious

You can learn more from these University sources:

• Fire Blight – Penn State University
• Fire Blight – University of Missouri
• Fire Blight – Purdue University

Conclusion

Now you know what fire blight is and how it spreads. You also know how to prevent it and slow its spread.

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