Pear Blossom Blast
Beginner
This pest affects:
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Scientific Name
Pseudomonas syringae pv. syringae
Identification
Injury is concentrated in the lower portion of the tree.
Fruit
- Blackening of the calyx end of individual fruitlets
- Blackening of blossom cluster base while cluster leaves appear normal
- Dead clusters including blossoms and leaves
- Fruit buds fail to open, turn brown, and may drop off
- Depressed, shiny black spots on fruit with post bloom infections
Leaves
- Depressed, shiny black spots up to 3 mm in diameter with post bloom infections
- Red ring frequently surrounds blackened tissue, especially on leaves
Shoots
- Most common on 1-year old shoots
- Bark cankers begin as brown, irregular patches and infected outer bark later sloughs off
- Dieback of twigs and spurs
Blossom blast can severely reduce crop yield, number of leaves, and number of fruit spurs in the trees.
Often Confused With
Fire blight – cankers extend more than 5 cm into a spur; bacterial ooze produced following rain; shepherd’s crook with dead leaves remaining attached
Boron deficiency –Boron deficiency causes blossoms to wither, similar to blossom blast. However, outer bark of shoots affected by blossom blast may separate from underlying tissue, taking on a papery appearance
Frost injury – occurs primarily in lower part of tree; both flowers and leaves injured; no twig dieback
Period of Activity
In the spring, plant tissue is most sensitive to freezing and incidence of frost is high. Pears can be affected by this disease from bud break through to fruit set, however are most susceptible to blossom blast between tight cluster and full bloom.
Scouting Notes
Monitor orchards from petal fall to 1-2 weeks after fruit set for symptoms after conditions were conducive to blossom blast infection.
Threshold
There are no thresholds for treatment.
Advanced
This pest affects:
|
Scientific Name
Pseudomonas syringae pv. syringae
Identification
Injury is concentrated in the lower portion of the tree.
Fruit
- Blackening of the calyx end of individual fruitlets
- Blackening of blossom cluster base while cluster leaves appear normal
- Dead clusters including blossoms and leaves
- Fruit buds fail to open, turn brown, and may drop off
- Depressed, shiny black spots on fruit with post bloom infections
Leaves
- Depressed, shiny black spots up to 3 mm in diameter with post bloom infections
- Red ring frequently surrounds blackened tissue, especially on leaves
Shoots
- Most common on 1-year old shoots
- Bark cankers begin as brown, irregular patches and infected outer bark later sloughs off
- Dieback of twigs and spurs
Blossom blast can severely reduce crop yield, number of leaves, and number of fruit spurs in the trees.
Often Confused With
Fire blight – cankers extend more than 5 cm into a spur; bacterial ooze produced following rain; shepherd’s crook with dead leaves remaining attached
Boron deficiency –Boron deficiency causes blossoms to wither, similar to blossom blast. However, outer bark of shoots affected by blossom blast may separate from underlying tissue, taking on a papery appearance
Frost injury – occurs primarily in lower part of tree; both flowers and leaves injured; no twig dieback
Biology
The bacterium, Pseudomonas syringae, survives on the surface of plant tissues. Blossom blast is a disease favoured by cool, wet spring weather. Cold temperatures or frost around bloom can increase the incidence of blossom blast. Symptoms usually develop 3-7 days after cool (0-12 C) wet weather. Damage occurs when the bacteria produce a toxin that destroys plant tissue as bacteria multiply in a wound. The relationship between this bacteria and infection during cold periods is complicated further by the fact that the bacteria produce proteins that act as ice crystal formation sites, causing freeze damage at higher temperatures than would ordinarily be the case. The bacteria can then colonize the frozen tissue, causing fruit and foliage infections.
Period of Activity
In the spring, plant tissue is most sensitive to freezing and incidence of frost is high. Pears can be affected by this disease from bud break through to fruit set, however are most susceptible to blossom blast between tight cluster and full bloom.
Scouting Notes
Monitor orchards from petal fall to 1-2 weeks after fruit set for symptoms after conditions were conducive to blossom blast infection.
Threshold
There are no thresholds for treatment.
Management Notes
Some cultivars, including Bartlett, Anjou and Bosc, are more susceptible to blossom blast infections. Asian pears seem to be more severely affected, likely because they bloom earlier and are more exposed to frost injury. Red Anjou and Bartlett varieties, as well as Comice often have less severe symptoms of blossom blast.
Avoid frost damage by choosing sites with good air drainage or use wind machines.
Minimize cover crop early in the season to keep orchards warmer.
Prune and destroy any affected tissue to lower the inoculation potential for the future.
Accurate disease identification is the important first step before management measures can be implemented. When in doubt, have infected tissues examined by a qualified lab such as the Pest Diagnostic Clinic at the University of Guelph or an experienced plant pathologist.
There is no chemical control registered for managing blossom blast. Blossom blast infection periods and symptoms generally appear earlier than fire blight would. Hence, streptomycin or copper applications targeted for fire blight will most likely be too late to help reduce blossom blast.
Some of the information included above was excerpted from:
