Fire Blight

What is Fire Blight?

Fire blight is a destructive bacterial disease primarily affecting members of the Rosaceae family. It’s named for the blackened, scorched appearance of infected branches, making them look as if they were burnt.

Fire blight primarily affects plants within the Rosaceae family. This includes:

• Apple, crabapple trees
• Pear (Pyrus species) trees
• Serviceberry (Amelanchier species) trees
• Roses (Rosa species)
• Raspberry and blackberry (Rubus species)
• Cotoneaster, hawthorn, mountain ash, and other ornamental plants

What are the Symptoms?

Flowers:

• Blossom Blight: This is one of the earliest and most noticeable symptoms. Infected flowers initially appear water-soaked, then they turn brown or black and shrivel. However, they often remain attached to the tree.
• Oozing: In humid conditions, a sticky, cloudy bacterial ooze can be exuded from the infected blossoms.

Leaves:

• Wilting: Leaves on infected shoots wilt rapidly and turn brown or black. They give a scorched or burned appearance, hence the name “fire blight.”
• Shepherd’s Crook: The blackened leaves at the tips of branches often curl, resembling a shepherd’s staff or crook.
• Hanging Leaves: Infected leaves tend to remain on the tree rather than fall off, giving a “blighted” appearance even in seasons where leaves would typically drop.

Fruit:

• Fruit Lesions: Infected fruits exhibit darkened, shrunken spots. Over time, they become shriveled and resemble mummies.
• Hanging Fruit: Infected fruits tend to remain attached to the tree longer than healthy ones, further contributing to the “blighted” appearance of the plant.

Bark:

• Cankers: Infected bark areas form sunken, darkened lesions or cankers. These cankers often have a water-soaked appearance initially, becoming darker over time.
• Cracking: The bark over cankers may crack, revealing the underlying infected wood.
• Oozing: The cankers on the bark can also produce a sticky, bacterial ooze, which may streak down the bark’s surface, especially in the spring.
• Reddish Streaks: In some cases, reddish-brown streaks can be seen in the wood beneath the bark of infected branches.

Understanding these symptoms can aid in the early detection and management of fire blight, helping to curb its spread and reduce its impact on the affected plants. It’s crucial to act promptly once any of these symptoms are spotted.

What Causes Fire Blight?

Fire blight is caused by the bacterium Erwinia amylovora, which thrives under specific environmental conditions. Recognizing these conditions can help in predicting and managing potential outbreaks.

Temperature and Moisture:

• Warm and humid conditions are especially conducive to the spread of fire blight. The disease proliferates when daytime temperatures range between 75°F and 85°F (24°C and 29°C) and nighttime temperatures stay above 60°F (16°C).
• Wet conditions, whether from rain, dew, or overhead irrigation, provide the moisture needed for the bacteria to infect plants. These conditions allow the bacterium to ooze out of the infected plant, where it can be spread by rain or insects.

Insect Activity:

• Warm weather also encourages insect activity. Insects, particularly bees, can spread the bacterium between flowers when they move from one bloom to another.

Wind and Rain:

• Wind-driven rain can splash the bacteria from infected tissues to healthy ones, aiding in its spread.

Plant Injury:

• Hail, heavy winds, or any other factors that cause wounds to the plant can provide entry points for the bacterium. Even pruning during the active growing season, when the bacterium is present, can lead to new infections.

Susceptible Growth Stage:

• New shoots and open blossoms are particularly susceptible. Hence, the periods of rapid plant growth and flowering, typically spring and early summer, pose the greatest risk for fire blight infection.

High Nitrogen Levels:

• Plants that have been excessively fertilized, especially with nitrogen, tend to have a lot of soft, new growth, which is more susceptible to fire blight infection.

Understanding the environmental conditions that favor fire blight is crucial for its management. By being aware of these factors, growers and gardeners can make informed decisions, like avoiding pruning during high-risk periods or adjusting irrigation practices, to reduce the likelihood of an outbreak.

How to Control and Prevent Fire Blight?

• Resistant Varieties: Choose plant varieties known for their resistance to fire blight.
• Prune Affected Areas: Regularly prune and dispose of infected branches. Always disinfect pruning tools between cuts.
• Avoid Excess Nitrogen: Over-fertilizing can promote the disease.
• Antibacterial Sprays: Applying antibacterial sprays during bloom can reduce the risk.
• Proper Watering: Water at the base of the plant rather than overhead to reduce splashing.
• Regular Inspections: Regularly inspect plants for signs and act promptly.