We've been getting calls this summer from gardeners finding fire blight damage in backyards and landscapes. Fire blight is usually associated with wet springs. Although spring 2014 wasn't particularly wet, rain occurring when apples, pears, quince, cotoneaster, and pyracantha are in bloom can induce the disease even in dry years.

The malady is called fire blight because terminals of affected branches suddenly blacken and die as if they've been scorched by fire (Figure 1). The disease is caused by the bacterium Erwinia amylovora, which commonly enters trees and shrubs through blossoms in rainy weather. Ideal conditions for disease development are rainy or humid weather with mild daytime temperatures (75° to...