Fire blight is a bacterial disease mostly affecting apples, pears, Asian pears, and close relatives like quinces and hawthorns. It gets its name because it causes young fruits, shoots, and branch tips to appear blackened and shriveled, as though scorched by fire. Dead leaves remain on the tree and shoot tips curl downward.
Fire Blight Pathology
Fire blight is mostly contracted through spring blossoms of fruit trees. Honeybees can be a carrier of the disease after they’ve pollinated an infected blossom. Once a tree is infected, it carries the disease indefinitely unless removed through pruning. An infection can be spread from the blossoms and branch tips to the rest of the tree and appears as a black discoloration in the bark. If left unchecked, fire blight can continue to spread to major limbs and the trunk and eventually kill the tree entirely.
Weather conditions greatly affect the rate of initial infection. The disease is most seriously spread during wet springs, especially if it is warm and rainy during bloom-time or pre-boom.
Fire Blight Treatment and Prevention
It is important to take action early in order to most effectively prevent the spread of Fire Blight. In the growing region in and around Philadelphia, you may begin to observe signs of infection in late spring, around May 25th. If you notice signs of infection, keep these things in mind:
- If possible, wait until the weather is dry before pruning. Infection spreads through moisture and rainwater.
- Try to cut out infection before the signs of necrosis (singed/ burned appearance in leaves).
- It is most effective to prune trees where there is a low incidence of fire blight.
- Always prune into healthy wood, 6 to 12 inches below the visible signs of fireblight.
- When pruning larger limbs, consider using the ugly stub method: make a cut about 6-12 inches below the fireblight and if the location of the cut is awkward, then remove the remainder of the branch later during winter pruning.
- For disposal of infected branches, prunings should ideally be burned offsite from the orchard. If burning is impossible, you can dry out branches thoroughly and mulch them later with a chipper.
- It is not recommended to cut out infected shoots after terminal growth has stopped. When growth stops, the spread of fire blight should also stop.
- During the summer, the best way to prevent additional fire blight spread is to control sucking insects like aphids and leafhoppers.
An otherwise healthy tree showing signs of Fire Blight can be cared for and managed through pruning of damaged areas. Prune off diseased wood as soon as you notice it to prevent it from spreading. Pruning cuts should be made into healthy wood, at least 6 to 12 inches below where you see any sign of infection.
It is very important to sterilize your tools between each pruning cut (a good general practice anytime you’re pruning during the active growing season) to avoid spreading the disease. Use rubbing alcohol (70% concentration preferred) or a 10% bleach 90% water solution to sterilize. This can be done by dunking or wiping your pruner or saw blade or by using a spray bottle to coat the blade in between each cut.
Prevention of Fire Blight starts with selecting disease resistant varieties of your trees (see link below). A copper sulfate spray in early spring can also reduce the rate of infection. Unfortunately, there is no ultimate cure for Fire Blight, and the best way to avoid it is to carefully monitor your trees for early signs and take preventative measures.
Some POP Recommended Cultivars with Fire Blight Resistance:
Apples: Liberty, Enterprise, Goldrush, Arkansas Black
European Pears: Harrow Sweet, Seckel, Moonglow, Potomac
Asian Pears: Shinko, Chojuro, Kosui, Tsu Li