Fire blight of apple and pear in Washington

Abstract

Fire blight is an important disease affecting pear and apple. Infections commonly occur during bloom or on late blooms during the three weeks following petal fall. Increased acreage of highly susceptible apple varieties on highly susceptible rootstocks has increased the danger that infected blocks will suffer significant damage. In Washington there have been minor outbreaks annually since 1991 and serious damage in over 5% to 10% of orchards in 1993, 1997, 1998, 2005, 2009, 2012, 2015, 2016, 2017, and 2018. Controlling fire blight is a significant expense for pome fruit producers. For example, in epidemic outbreaks in Washington in 2017 and 2018 growers reported spending an average of $250 an acre on preventative sprays and$27 to $864 per acre for removal of cankered wood as well as removal of more than 300 acres of apples and 200 acres of pears