WSU Extension


Caption: Pseudomonas cankers on pear twigs
Photo by: R.S. Byther
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Ornamental Pear : Pseudomonas blossom blast and dieback
(revision date: 1/27/2016)

Blossom blast and dieback is caused by a bacterial infection. The infection causes buds to turn a papery brown and die. Leaves may be spotted. Flower petals and stems may also be affected, and fruit cluster bases can turn brown or black. Occasionally, fruiting spurs may be killed. Cankers may develop in twigs and branches. Symptoms of this disease, especially on flowers, may closely resemble fire blight. However, blast infections seldom extend more than 1"-2" into a spur. Bacterial ooze, which is common with fire blight, is not present with Pseudomonas blast. Fruiting pears and most Asian pear cultivars are also susceptible. Frost and cold injury promote infection, which is common in cold, wet springs. Warm, dry weather inhibits disease.
Management Options

Non-Chemical Management
  • Avoid wounding plants.
  • Prevent frost injury when possible. Plant hardy varieties in protected locations.
  • Provide proper culture to minimize amount of succulent shoot growth and to reduce injuries.
  • Prune out and destroy infected tissues as soon as they are noticed. Make cuts at least 6" below infected areas and sterilize pruning tools between cuts.
Select non-chemical management options as your first choice!

Chemical Management

Apply before fall rains and again before spring growth starts. Excessive amounts may cause russetting on fruit (if present). 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.

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 reg no: 4-58
  • Bonide Liquid Copper Fungicide Conc/Organic Gardening
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-4
  • Soap-Shield Flowable Liquid Copper Fungicide [Organic]
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-56872
  • This list may not include all products registered for this use.
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Caption: Pseudomonas cankers on pear twigs
Photo by: R.S. Byther