This bacterium is one of the most troublesome diseases of the apple, pear, and quince but can also affect flowering plum, cotoneaster, cockspur thorn, pyracantha, and others from the rose family. The Pathogen is the bacterium Erimina amylovora which is carried by splashing rain, bees, flies, and other insects. It can also be spread by improper sanitation of pruning tools.
In nature insects infect blossoms in the spring and can be rapidly transmitted from tree to tree. From the blossom they travel downward to the fruiting spurs, twigs and eventually larger branches. Symptoms appear in the spring as a sudden browning or blacking of flowers and leaves near the twig tips. Twigs, and eventually larger branches, die.