Fire Blight

Problem type: Disease

Name of problem: Fire Blight

Plant name(s): Apple, mountain ash, cotoneaster, pear, saskatoon, rose, spirea, hawthorn

Symptoms / Characteristics:
Primary symptoms occur in blossoms, fruit and succulent new shoots. Individual flowers or entire flower clusters appear water soaked, quickly drooping, shriveling and turning brown. Most infections occur in the blossoms, then move into flower or fruit stalks and then into twigs. Leaves and flowers near growing tips suddenly wilt, turn brown or black and appear to have been scorched by fire, hence the name fire blight. The end of the diseased twig or branch becomes hooked, having the characteristic appearance of a "shepherd's crook".

Infections can progress into larger branches and into the main stem where cankers may form unnoticed. Cankers begin as small brown to black sunken areas and as healthy tissue grows around them, they become more noticeable. During wet weather, an amber ooze may emerge from infected areas which is filled with bacteria that is ready to infect new tissue. If the bark is peeled away at these infected bark areas, the inner tissue will be discolored reddish brown.

Fire blight is a bacterial disease caused by the bacterium Erwinia amylovora. The disease is favored by moist weather and temperatures around 25-30°C. Symptoms usually do not appear until 1-3 weeks after infection has taken place, depending on temperature and moisture. Bacteria can be spread by pollinating bees and other insects, birds, splashing rain and pruning tools. Infections take place at openings in the plant such as floral parts, succulent leaves and twigs and wounds caused by things such as improper pruning or hailstorms. The bacterium overwinters in infected branches. When warm, wet weather arrives in spring, bacterial activity begins. Fire blight can cause disfigurement and even death of an entire tree if left untreated.

Control / Preventions:
Infected twigs or branches should be pruned off, making cuts at least 20 cm below the canker or burnt areas. Pruning should take place when all plant surfaces are dry, and preferably during cold weather in the fall. Pruning tools should be sterilized in a 10% bleach or 70% ethanol solution between each cut. Suckers growing from the base of the tree should be removed as this soft growth is easily infected. Avoid fertilizing plants with high levels of nitrogen as this also promotes succulent growth. Sprays containing fixed copper can be applied as a preventative measure during blossom. Repeat applications may be needed if rain occurs within 72 hours of application.

Controlling other insects such as leafhoppers, aphids and other leaf feeding insects will help control spread of the disease. Regularly inspect trees and shrubs for any sign of fire blight so quick action can be taken.