Fire Blight is prevalent this year, with Swingle experts reporting occurrences up and down the Front Range. Fire Blight is a destructive bacterial disease affecting many types of fruit trees and ornamental shrubbery. Apple, crabapple, and pear trees are common targets, but it can also affect hawthorn, mountain ash, serviceberry quince, pyracantha and other species in the rose family.
Damage: Symptoms can be seen on flowers, fruit, limbs, leaves, and the main trunk. Blighted limbs have a water soaked appearance and characteristics “shepherds crook” as their tips and leaves die, turning brown and black. They typically will remain on the plant. Infected branches turn reddish color, which also distinguishes where the disease progression has stopped.
Life Cycle: In spring when environmental conditions are favorable, the bacteria become very active entering through blossoms, cracks, and wounds.
Management: Pruning of infected wood during the dormant period (typically November through April) is the best practice for managing Fire Blight. Environmental conditions may cause re-infection during the growing season.
Good Cultural Practices: Planting resistant varieties, dormant pruning, disposal of infected wood, and avoidance of excessive fertilization to reduce excessive shoot growth are recognized practices. Re-infection may still occur regardless of proper cultural practices.
Frequently Asked Questions:
Q: How did my tree get this disease and my neighbor’s trees did not?
A: Tree susceptibility to disease varies by variety of the tree, its health and the growing location. Humidity and temperature can vary widely even in the smallest of areas allowing different activity to occur within a few feet.
Q: My trees were sprayed, how did I get this disease?
A: Most tree spray application only target aphids, mites, and caterpillars. Fruit trees often times should not be sprayed due to fruit contamination. The disease occurs when temperatures and humidity are high. Insects and rain also cause the bacteria to spread, especially in hail damaged trees with open wounds.
Q: What can I do? My trees look terrible!
A: Unsightly yes. You should wait to prune in late fall because tree pruning now in Denver may promote significant spread of the disease.
Q: What should I do in the future to prevent this from happening again?
A: Swingle does not offer a preventative application. You may find some literature suggesting spray applications. We have found these to be ineffective or require multiple sprays timed perfectly which is difficult to achieve.