Key Features
- Blackened leaves
- Dark brown blighted branches
- Sunken, darkened cankers
Symptoms
The name "fire blight" comes from the blackened leaves that are characteristic of infections. After infection, blossoms wilt and turn brown. The tips of affected branches curl downward in a 'shepherds crook.' This shoot blight develops into cankers, that are are dark, sunken areas on a stem, often with cracked or peeling bark. Droplets of bacteria ooze form on the surface of infected branches or fruit. Leaves on affected branches turn deep brown or black and remain on the branch. Flowers wilt and turn brown while fruit shrivel. Shriveled fruit will remain on the plant well into the fall and winter.
Biology
Bacterial ooze is splashed or carried by insects from infected tissue to natural openings or wounds in susceptible plants. Infection often begins on flowers, new leaves, wounds (especially after freeze damage or hail), and natural openings on new growth. The bacteria move from the site of infection back toward the trunk of the tree in water and nutrient transpoting tubes. Poor pruning practices, such as pruning infected trees when trees are wet, easily spreads the disease.
Management Recommendations
The use of resistant varieties is the only reasonable means of managing this problem in the urban landscape. Fireblight resistant cultivars are available for crabapple, flowering pear, firethorn, cotoneaster, flowering quince, hawthorn, and mountain-ash. Planting susceptible cultivars in a location that provides more than six hours of sunlight per day, correct fertilization and adequate tree spacing will reduce the risk of infection. Pruning should only be performed in dry weather, and cuts should be made at least 18 inches below (toward the trunk) beyond the lower end of the canker. All infected material should burned or disposed of. Composting may not completely kill the bacteria. Pruning equipment must be sterilized between cuts by dipping in a solution of 10% bleach with a few drops of detergent (soap). Excessive pruning can increasing the risk of infection. Plants that have more than 50% of their canopy infected should be removed. Streptomycin is effective in reducing the the flower infecting stage of this disease (blossom blight) but should not be used to treat trees already infected. Streptomycin should be applied at first open blossoms, and again 1-2 more times until flower petals have fallen.
Effective Pesticides
Active Ingredients include: Copper salts, Streptomycin
Resources
- Fire Blight
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
