Utah State University Extension
In spring 2007, conditions in Utah were optimal for fire blight infection on blooming apples. At least 5 days had favorable conditions that resulted in high infection risk. By late spring, it was apparent that there were severe losses in many Utah orchards. Severe infections in sensitive apple blocks also occurred in 2008 and 2009. Because this disease moves invisibly and rapidly, it can catch growers off guard. Having a well executed and integrated year-round management program can reduce fire blight inoculum and future infections.
Murray, Marion, "Fire Blight Annual Management Guide for Utah" (2010). All Current Publications. Paper 902.