WSU Extension


Mountain Ash
Fire blight 
Nectria canker 
Ash borer 
Leaf blister mite 
Mountain ash sawfly 

print version| pdf version| email url    
Caption: Cotoneaster fire blight
Photo by: R. Maleike
Mountain Ash : Fire blight
(revision date: 4/11/2018)

Fire blight is a bacterial infection of shoots which enters the plant through blossoms, vigorously growing shoot tips, young leaves, and wounds. Blossom clusters appear blighted. Shoots suddenly wilt, turn black and die back, presenting a "scorched" appearance. Purplish cankers may develop on the shoots. During wet or warm weather, the cankers may ooze brown sticky droplets. Newly infected wood is reddish, while older infections are black. The bacteria are easily spread by rain and pollinating insects. Fire blight also affects pear, pyracantha, apple, and related species. It is not a proven problem in western Washington.
Management Options

Non-Chemical Management
  • Immediately prune out and destroy infected tissues. Make pruning cuts at least 6" below infected tissues. Sterilize tools between cuts. Do not do regular pruning at the same time as blight removal.
  • Avoid wounding plants.
  • Use moderate amounts of nitrogen fertilizer to minimize vigorous growth of susceptible shoots.
Select non-chemical management options as your first choice!

Chemical Management

Apply during prebloom and bloom period. 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 Liquid Copper Fungicide Conc/Organic Gardening
    Active ingredient: copper octanoate  |  EPA reg no: 67702-2-4
  • This list may not include all products registered for this use.

+ Show larger images

Caption: Cotoneaster fire blight
Photo by: R. Maleike