Fire blight is caused by the bacterium Erwinia amylovora. It is a common disease of apple, pear, and quince trees, as well as ornamentals such as roses, crabapple, pyracantha hawthorn, cotoneaster, photinia, evergreen pear, and loquat trees.
Disease symptoms appear in spring as the trees produce new, active growth. The first sign is a watery ooze that seeps from the branch, twig, or trunk of the infected plant. The ooze turns dark after exposure to air. Flowers and leaves of the infected plant wilt and turn brown or black. Cankers appear, and any developing fruit shrivels and turns black. Dead, blackened leaves and fruit will cling to branches throughout the season. The tree or infected plant may have a scorched appearance, or look blighted.
The bacterium easily spreads by rain, birds, insects, or animals. Even gardeners can transmit the disease with infected gardening tools or when watering. The maximum risk of infection is late spring or early summer when diseased tissues and ooze from branches or twigs start to surface. Fast growing shoots can be severely affected. High soil fertility and soil moisture increase the severity of damage to trees.
There is no cure for fire blight. To control its spread from diseased to healthy plants, remove diseased stems and branches by pruning eight to twelve inches below the infected areas. Since the bacteria are easily transmitted, take extreme care when disposing infected plant material. Tools used to prune infected vegetation should be sterilized in a 10 percent bleach solution and wiped dry after disinfecting.
A weak solution of a copper fungicide can be applied to open blossoms. This will help reduce new infection but will not eliminate existing infections in the stems or wood. Copper fungicide sprays are best when used during the tree’s dormant period, or at bud break. Be aware that the fungicide can cause scarring if applied to fruit. Neither should you spray it within fifty days of fruit harvest. Always read the label carefully and apply only as directed. Consult your local Cooperative Extension Service for updated information.
To proactively lessen the danger of fire blight, consider using resistant varieties of plants; different varieties of fruits and ornamentals have varying degrees of susceptibility to the disease. No variety is immune, however, when conditions are favorable and the pathogen is abundant. The structure and mineral content of the soil are important in managing fire blight, too—trees planted in poorly draining soils are more susceptible to the disease.