What causes my apple and pear trees to look like they have been burned with a torch?

A disease called fire blight, caused by a bacterium (Erwinia amylovora), has these symptoms. The causal bacteria are spread by wind-blown rain and insects. Fire blight is difficult to control in highly susceptible varieties. Avoid excessive nitrogen fertilizer. The blighted shoots and blossoms can be pruned out as they appear if you sanitize the pruning shears by dipping them in a 10 percent bleach solution or 70% isopropyl alcohol (rubbing alcohol) between cuts. Otherwise, prune the blighted shoots …