Pear: Fire blight

Biology

Fire blight is a bacterial infection which typically attacks via wounds or blossoms. Initially, twigs and flowers appear water-soaked. Infected tissues quickly turn brown to black and die back, often bending over in a “shepherd’s crook”. Blighted tissues remain on the tree, giving it a scorched appearance. Dark, somewhat sunken cankers develop on twigs and branches, sometimes girdling the limb and causing dieback. A brownish bacterial ooze is common at the margins of cankers, especially during humid weather. Fruit may also be infected, showing sunken black spots up to 1″ in diameter and 1⁄4″ deep. The bacteria overwinter in infected tissues and can be transmitted by rain and pollinating insects. Fire blight is not a proven problem in western Washington. Pseudomonas blossom blast and dieback is caused by a different species of bacteria, but the symptoms may be similar.

Management Options

Use Integrated Pest Management (IPM) for successful plant problem management.

Non-chemical Management

Select non-chemical management options as your first choice!

• Plant resistant varieties when possible. ‘Giant Seckel’, ‘Mac’, ‘Maxine’, and ‘Moonglow’ are reported to be somewhat resistant.
• Prune out and destroy infected tissues when noticed. Make cuts at least 6″ below infected areas and sterilize pruning tools between cuts. To reduce chances of spreading bacteria, do not perform blight removal during regular pruning.
• Provide proper culture to minimize amount of succulent shoot growth and to reduce injuries including winter injury.
• Avoid wounding plants.

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.

• Bactericidal sprays applied during the main bloom season are very effective.
• Do not apply copper products to ‘Anjou’, ‘Comice’ or ‘Forelle’ pears or severe russeting may occur.
• Homeowners should not make foliar applications to trees over 10 ft. tall.
• Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Approved Pesticides

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

• Bonide Copper Fungicide Spray or Dust RTU [Organic]
  Active ingredient: basic copper sulfate [EPA registration number: 4-58]
• Bonide Liquid Copper Fungicide Concentrate/Organic Gardening
  Active ingredient: copper octanoate [EPA registration number: 67702-2-4]
• Monterey Liqui-Cop Copper Fungicidal Garden Spray
  Active ingredient: copper-ammonia complex [EPA registration number: 54705-7]
• Soap-Shield Flowable Liquid Copper Fungicide [Organic]
  Active ingredient: copper octanoate [EPA registration number: 67702-2-56872]
• This list may not include all products registered for this use.

Additional Images