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 during the winter, before the new growing season starts. The bacteria overwinter on the infected wood. The overwintering population can be reduced by spraying the trees with copper fungicide in the early spring, before bud break. A bactericide, such as streptomycin, can be sprayed on the blossoms, every three to five days when average daily temperatures are above 60 degrees F; do not use bactericide before or after the bloom period. Plant resistant varieties (i.e., Red Delicious and its strains) so that these practices will not be necessary.