Blossoms are usually infected first and have a water soaked appearance. Eventually the blossoms will wilt, shrivel and turn black. The most characteristic symptoms are blackening of leaves, shoots and, in severe cases, branches. A sticky ooze, which contains millions of bacteria, will seep from the infected area. Cankers may become visible from the summer months onwards.
Bacteria can overwinter in the cankers and become active again in the spring.
A susceptible pear seedling showing typical symptoms of fire blight. Typical shepherds crook symptoms of fire blight on shoots and leaves. Bacterial blast usually affects the blossoms and surrounding leaves. Outbreaks of fire blight can occur anywhere in New Zealand under the right conditions. World-wide, the disease is found throughout North America and Canada and much of Europe.