The fire blight pathogen kills fruit-bearing spurs, branches, and often entire trees. Infected blossoms become water-soaked and then wilted, changing in color to dark green and then black. Infected shoots turn brown to black from the tip and bend near the tip to resemble a shepherd’s crook. Fire blight cankers are large black areas that can become sunken and cracked. Internally infected branches appear darker than normal.
Fire blight can kill trees of any age by infecting the rootstock, although younger trees are most susceptible. Younger trees with rootstock blight die quickly. The wood of older trees appears lighter and the trees produce conspicuously fewer blossoms and leaves during the 1- to 2-year period of decline prior to tree death. Are conditions right for fire blight?
Forecast models for fire blight available at Enviro-weather. Select a weather station from the map that is closest to your location. Then click on “fruit” for a list of weather resources and models for fruit production.
Monitoring: The presence of bacterial ooze is the most conspicuous sign of fire blight infection. Milky-colored to reddish brown ooze can be seen on blighted blossoms and shoots, infected fruits, and emanating from cankers in the spring.
Scouting for cankers should be done when trees are dormant; pruning to remove cankers should be done at this time.
Fire blight cankers on Jonathan apple.
Decling 'Gala' apple tree with rootstock fire blight. Photo credit: M. Longstroth
More on fire blight at MSU Extension educator's Mark Longstroth web site