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Ministry of Agriculture, Food and Rural Affairs

Fire Blight - LIMB & TRUNK

Severely infected trees with fire blight appear to be “scorched” by fire Fire blight canker becomes sunken with cracked margins with bacteria oozing out onto the surface of the canker
Click to enlarge.

Beginner

Scientific Name
Erwinia amylovora

Identification           

  • Fire blight attacks many different parts of the tree, and fire blight symptoms are often referred to by the part of the tree attacked – blossom, shoot, fruit, limb and trunk, and collar or rootstock blight.

Limb and trunk blight:

  • Progresses into the main limbs and trunk of the tree from infected spurs or shoots when ideal temperature and humidity conditions are present.
  • Cankers in the older wood girdle the branch, killing healthy wood from that point outward.
  • Cankers first appear brown to purple, eventually sunken with cracked margins.
  • The tissue under the bark initially appears water soaked, eventually with red streaks and finally turns brown.
  • During rainy or very humid periods, bacteria ooze, at first milky white, quickly becoming brown, onto the surface of the cankers.
  • The ooze dries out and remains as a gummy substance or completely dries to an amber resin-like substance and remains for several months.
  • In the winter, cankers usually dry up and become inactive. In the spring, cankers can expand.
  • Infections spread into adjacent water sprouts, shoots and limbs resulting in canker blight.
  • Canker extension may begin before, during or shortly after bloom.

Often Confused With

Period of Activity
Fire blight cankers can be present in orchards from dormant through harvest.

Scouting Notes
When scouting for fire blight, it is important to recognize the stage of development and what it is important to be monitoring for. While the tree is in dormancy, look for cankers that are overwintering in the orchard. Sprays aimed at managing fire blight occur from bloom through petal fall.  Refer to blossom blight for more information on the timing of these sprays. It is important to scout for cankers that appear to be oozing and blossoms that appear to be infected. While the shoots are actively growing, monitor for terminals that appear to have the characteristic shepherds crook. These deformations of the terminals are indicative of a fire blight infection.

Thresholds
It is important to have knowledge of prior out breaks of fire blight in orchards. If a history is known, use proper management tools to deal fire blight during weather periods that are conducive to possible outbreaks.

For information on the use of models for timing sprays for fire blight refer to blossom blight.

Advanced

Scientific Name
Erwinia amylovora

Identification           
Fire blight attacks many different parts of the tree, and fire blight symptoms are often referred to by the part of the tree attacked – blossom, shoot, fruit, limb and trunk, and collar or rootstock blight.

Limb and trunk blight: The most severe losses from both blossom and shoot blight occur when the disease progresses into older wood. Fire blight progresses into the main limbs and trunk of the tree from infected spurs or shoots when warm temperatures with high humidity combine to form ideal conditions for fire blight. The cankers that form in the older wood girdle the branch, killing healthy wood from that point outward by cutting off the transport of nutrients and water. The cankers first appear brown to purple in colour. Eventually they become sunken with cracked margins. The tissue under the bark initially appears water soaked, eventually with red streaks and finally turns brown. During rainy or very humid periods, bacteria ooze onto the surface of the cankers. At first, bacterial ooze appears a milky white drop but quickly becomes brown upon exposure to air. The ooze dries out and remains as a gummy substance or completely dries to an amber resin-like substance on canker surfaces where it remains for several months. In the winter, cankers usually dry up and become inactive. In the spring, renewed activity at the margins of cankers results in the extension of the cankers. Infections extend and spread into adjacent water sprouts, shoots and limbs resulting in canker blight. Canker extension may begin before, during or shortly after bloom, depending on the environmental conditions experienced during the spring in the orchard.

Often Confused With

Biology
Refer to the blossom blight infosheet for information on the biology of Erwinia amylovora, the bacteria that causes fire blight. 

Period Of Activity
Fire blight cankers can be present in orchards from dormant through harvest.

Scouting Notes
When scouting for fire blight, it is important to recognize the stage of development and what it is important to be monitoring for. While the tree is in dormancy, look for cankers that are over-wintering in the orchard. Sprays aimed at managing fire blight occur from bloom through petal fall.  Refer to blossom blight for more information on the timing of these sprays. It is important to scout for cankers that appear to be oozing and blossoms that appear to be infected. While the shoots are actively growing, monitor for terminals that appear to have the characteristic shepherds crook. These deformations of the terminals are indicative of a fire blight infection.

Thresholds
It is important to have knowledge of prior out breaks of fire blight in orchards. If a history is known, use proper management tools to deal fire blight during weather periods that are conducive to possible outbreaks.

For information on the use of models for timing sprays for fire blight refer to blossom blight.

Management Notes
Cultivar and rootstock susceptibility
All apple cultivars and rootstocks are susceptible to fire blight, however some are less susceptible than others. When planning new plantings, particularly in southwestern Ontario (below a line from Sarnia to Oakville), consider fire blight susceptibility when deciding what cultivars and rootstocks to plant.  For information on the susceptibility of cultivars and rootstocks to fire blight refer to OMAFRA Publication 310, Integrated Pest Management for apples.

Cultural management practices
To reduce the risk of fire blight incidence and spread in the orchard, the following cultural management practices are recommended.

  • Avoid over fertilizing with nitrogen. Excess nitrogen stimulates succulent growth that is susceptible to fire blight infection. Apply nitrogen fertilizer only where warranted by annual leaf analysis. Consider a split application of nutrients, half in the spring before growth starts and half again after petal fall. If severe blossom blight occurs, withhold the later application. Similarly, avoid late cultivation that can make nitrogen available to the tree resulting in late succulent growth.
  • In healthy trees, avoid excessive winter pruning which stimulates vegetative growth the following growing season.  Regular annual pruning and minimizing the number of cuts made keeps the tree “calmer”.
  • Delay summer pruning until terminal bud set has occurred (i.e. terminals “hardened off”), generally by early to mid August. Summer pruning to increase fruiting wood in high-density apple orchards encourages new shoot growth and extends the susceptibility period for shoot blight. If fire blight is present, disinfect pruning tools between each cut. However, sterilizing pruning tools is not required if the pruning is done well beyond the infection (30 cm beyond the visible symptom) such that the pruned section does not have dark concentric sections. In older orchards that are severely infected with fire blight, avoid summer pruning altogether. Remove spurs on the main trunk and scaffold limbs to eliminate their potential of infection.
  • Suckers (water sprouts) are good entry points for fire blight into large branches, limbs and trunks. Break them out periodically during the early growing season (i.e. June).
  • Prune infected trees during the dormant season to remove all overwintering cankers and sources of inoculum. Prune well beyond visibly infected areas.  For more information on pruning techniques to minimize the spread of fire blight refer to OMAFRA Publication 310, Integrated Pest Management for Apples.
  • Avoid using overhead irrigating to prevent excessive vegetative growth and reduce the spread of bacteria within the orchard.
  • Maintain good integrated pest management practices to minimize the spread of the fire blight bacteria by insects and to reduce insect-caused wounds to leaf and shoot tissue, which act as entry points for the bacteria. Good control of plant-sucking insects such as leafhoppers, aphids and plant bugs is particularly important. Conduct frequent (weekly) insect pest monitoring and use appropriate control measures where warranted.
  • Closely monitor non-orchard sources of fire blight such as susceptible ornamental plants or abandoned apple trees, hawthorn, mountain ash, cotoneaster and quince that are close to commercial orchards for signs of fire blight and cankers. Overwintering cankers are one of the primary sources of bacteria for subsequent infections. If possible, remove these host tree and shrubs from the vicinity of the orchards.
  • Scout orchards twice a week starting at bloom for blossom infections. Prompt removal of early bloom infections significantly reduces the impact of the disease later on in the season. Remove infected spurs by cutting at least 15 cm beyond the farthest signs of infection. If continual blossom blight is observed in a particular area of the orchard, scout for an active canker in the vicinity and remove it promptly.

When fire blight appears year after year in an orchard, use a more aggressive approach to keep this disease managed. For more information on managing fire blight see OMAFRA Publication 360, Guide to Fruit Production.

Chemical Management of Fire blight
For information on the use of chemicals to manage fire blight refer to the blossom blight infosheet.