Fruit trees are both a beautiful and beneficial addition to our landscape; however, their health can be threatened by a bacterial disease call fire blight.
Fire blight commonly attacks fruit trees and rosaceous ornamental trees including:
- mountain ash
Tree damage can range from mild disfiguration, loss of fruit, all the way to death.
When are my trees at risk?
The disease is most active in spring, favoring temperatures between 60 and 75 degrees Fahrenheit or prolonged rain and high humidity. Late spring is also the time when bacteria are emerging from a dormant plant.
Insects and birds are common transmitters of the disease, but we also play a role. Practices such as sprinkler irrigation, use of quick-release, high nitrogen fertilizer and use of un-sanitized pruning tools are all favorable to the spread of fire blight.
What should I look for?
As is in the name, fire blight causes many areas of a plant to appear to be burned by fire. The disease affects each part of the tree in similar ways.
Individual flowers or flower clusters appear to be water soaked and eventually drop, shrivel and turn brown or black.
Similar to the tree’s flowers, the fruit will turn brown or black and wilt. They too will eventually dry and shrivel on the tree.
Branches and Twigs
Later stages of the disease cause discolored oozing patches and cankers to form on branches. The cankers have a water soaked appearance before becoming sunken and dry. Twigs turn to a reddish-brown color and, often, form into an inverted U-shape. Overall, formation of twig and branch cankers can cause dieback.
Management and Treatment
Fire blight bacteria will continue to multiply as long as environmental conditions are favorable, so it is important to be proactive about treatment and management. A program of proper fertilization, irrigation, mulching and pruning will support the plant’s natural ability to combat this disease.
Pruning of all blighted twigs and branches can delay the spread of the disease. This practice is most effective when done during cool, dry periods in later winter, also known as dormant pruning. For best results, the branches and twigs should be cut 12 inches below infected tissue. After each cut, pruning tools must be disinfected using a 20% bleach to water solution.
To manage a newly budding tree, avoid use of quick-release, high nitrogen fertilizers. Chemical treatments for the tree should begin at budding and continue every 3 to 5 days until the end of bloom. After rainfall, immediately re-spray the tree.