Many members of the Rosa family are susceptible to fireblight. The susceptible species include roses, apples, crabapples, cotoneaster, hawthorn, pear, mountain ash, raspberry, Saskatoon, plum and cherry.
Fire Blight is caused by bacteria (Erwinia amylovora) that may enter the tree through blossoms, leaves or stem wounds. The bacteria overwinter in cankers in the main stem, branches or twigs of the infected tree. In the spring, when blossoms begin to open, the cankers exude sweet gummy bacterial ooze. This is spread to blossoms and young leaves mainly by rain, heavy dew or windblown mist. It can also be spread by pollinating bees and sucking, chewing or boring insects, and unsanitary pruning practices. Warm temperatures and high humidity are optimal conditions for infection and disease development.
In the spring, infected blossoms suddenly wilt and turn brown. Later the twigs and leaves turn brown and seem scorched by fire. The affected leaves usually remain on the tree well into winter. Young infected fruit becomes watery or oily in appearance and ooze a clear, milky or amber colored substance. They later become leathery, turn brown or even black depending on the species. The shrivelled fruit usually remains attached to the tree. The bark of branches becomes reddish and water soaked and later cracks and turns black.
The only effective method of control is pruning and destroying diseased twigs and branches. Make cuts at least 30 cm below the last sigh of infected bark. Sterilize pruners/saws after each cut. Trees that are severely infected with large cankers in the trunk should be removed and burned immediately.
For more For more information, please contact the Parks and Recreation Department.,