This integrated pest management (IPM) fact sheet provides information useful for identifying and combating a particular pest while minimizing environmental impact. It was originally written by Philip Dickey of the Washington Toxics Coalition and designed by Cath Carine of CC Design for the Green Gardening Program which is funded by Seattle Public Utilities. It has been modified for use on Toxipedia.org.

Species

Erwinia amylovora

Host/Site

Fire Blight is a bacterial disease that damages blossoms, shoots, limbs, and occasionally entire trees of apple and pear species. Fire blight can also, though less frequently, be found on quince trees, crabapple, fire thorn, cotoneaster, mountain ash, hawthorn, and raspberry plants. Contact local extension services for guidance.

Identification

Appearance
The bacteria can be visible on or near blossoms, shoots, and limbs of the tree. When the bacterium overwinters, a canker of discolored and cracked bark appears on trunks and larger limbs.

Blossom infestation generally occurs 1-2 weeks after initial blooming, and the flower cluster wilts, dies, and turns either brown or black depending on the plant species. The same symptoms apply to infected shoots.

For limbs, other than noticeable cankers, newly infected wood that lies underneath the first layer of bark will tend to have pink, or orange-red streaks of discoloration.

Brown rot on blossoms appears as sudden wilting and browning of flower parts.

Later, dead flowers may be covered by a grayish brown powdery mass of fungus spores. Fruit shows soft, brown spots, which may enlarge, rot, and become covered with spores. Diseased fruits such as plums may hang on the tree and dry to a firm, mummified state. On twigs and smaller branches, brown rot cankers are oval or elongated, definite in outline, brown in color, and usually sunken. The twig is sometimes girdled and dies. The sap may show as "gummy."

Life Cycle

Outbreaks of fire blight can be infrequent from season to season depending on weather, though an outbreak can be extremely damaging to subjected trees and orchards.

The bacterial pathogen that causes fire blight overwinter within the cankers and limbs of infected wood from the previous season. With warmer and consistent temperatures, the bacteria multiply and spread (noticeable with the tan ooze) and settle on the bark prior to blossoming. The ooze attracts flies, and flies become dispersal agents for the bacteria to spread to different trees.

Once the tree begins to grow, the bacteria continue to expand with the growing tree. The rate at which the bacteria spread is directly correlated to the vigor of the tree.

Natural Enemies

None

Monitoring

Action Threshold

If any infection is observed, both physical and chemical controls must be used in order to manage the disease and lessen the extent to which the tree will be damaged. If fire blight is left untreated, fruit will be diseased, and eventually the tree will die. Just one blossom infection can lead to the death of a limb, and infections on the trunk can kill most of the tree in one season.

Cultural and Physical Controls

The only alternative for preventing the risk of fire blight infections is to plant only species that have some resistance to the bacteria. Contact your local extension service for the most current recommendations.

For infected areas of the tree, physical removal of the limbs and shoots is a necessary requisite for control. Blighted limbs and shoots must be removed at least 8-12 inches below infected site (canker, etc). Bear in mind that on occasion the entire tree may need to be removed.

For a whole orchard subject to infection, at times it is most prudent to cut only limbs that threaten the main stem of the tree. Outer lying twigs and limbs should be removed when the tree is pruned again.

Biological Controls

None. It is possible that wound causing insects such as leafhoppers, plant bugs, etc., can create openings in which the bacteria can enter. Maintain a healthy pest management routine.

Chemical Controls

Organic copper sprays applied to infected areas can reduce the amount of bacterium on the surfaces of infected trees. Sprays will only reduce the damage incidence, not eliminate wood infections.