Pear tress can make a mess when unpicked fruit falls to the ground, and ripe fruit left to rot on the ground increases the chances of disease being spread to your trees. Too much fruit setting on a tree also increases the chances of broken branches. You can eliminate fruiting with a couple of simple techniques, and you don't have spray your trees with any potentially dangerous chemicals.
Prune most of last year's growth in late winter or early spring before the tree begins putting on new growth for the year. Most pears form on last year's growth.
Remove blooms as they appear. Use a water hose with a high-pressure nozzle to knock off any blooms that you cannot reach. Spray your tree thoroughly twice a week for two weeks, knocking off every bloom you can see. No blooms, no pears.
Pick off any stray pears that are still on the tree by hand or with a long pole.