Fire Blight: Recognizing and Managing a Common Fruit Tree Disease

If you grow apples, pears, crabapples, quince, or hawthorn in the Treasure Valley, fire blight is a disease worth watching for. Caused by the bacterium Erwinia amylovora, fire blight is one of the most destructive diseases affecting pome fruits and many ornamental plants in the rose family.

Fire blight affects apple, pear, crabapple, quince, hawthorn, cotoneaster, pyracantha, and mountain ash. While apples and pears often receive the most attention, many homeowners first notice the disease on ornamental landscape plants.
The bacterium survives the winter in cankers—sunken, infected areas on branches and trunks. As temperatures warm in spring, bacteria become active and may ooze from these cankers as sticky, amber-colored droplets. Insects attracted to the ooze can carry the bacteria to open blossoms. Rain, heavy dew, and splashing water can also spread the disease.

Infection is most common during bloom when temperatures are warm and moisture is present. One of the earliest signs is the characteristic "shepherd's crook," where young shoot tips wilt and bend over. Blossoms may turn brown or black and appear scorched. Leaves often remain attached to infected shoots, giving the tree a burned appearance. As the disease progresses, it can move into larger branches and form cankers. If a canker develops on the trunk or rootstock, it may girdle and kill the entire tree.

Prevention is the best defense against fire blight. When planting new fruit trees, select varieties and rootstocks with documented fire blight resistance whenever possible. Avoid excessive nitrogen fertilizer applications, which encourage lush, succulent growth that is more susceptible to infection. Proper spacing, pruning, and weed management can improve air circulation and help reduce humidity around trees.

Pruning is an important management tool. During the dormant season, remove old cankers and infected branches. Once fire blight is detected during the growing season, prune out infected shoots 12 to 18 inches below visible symptoms. Avoid pruning during wet weather, as bacteria can be spread by tools and splashing water. Severely infected young trees may need to be removed entirely.

Chemical controls are available but must be properly timed. Commercial growers may use antibiotic sprays during bloom when infection risk is high. Homeowners may have access to copper-based products labeled for fire blight suppression. Always read and follow label directions and apply products only according to label instructions.

Monitoring weather conditions and local fire blight forecasts can help determine when infection risk is greatest and when management practices will be most effective.