There may be several things going on with your pear trees. The sprouting suckers from the roots and your treatment of them with a sprout inhibitor may be unrelated to the leaf browning, although excess application of sprout inhibitor could cause some damage to the rest of the tree. It's also possible that your pear trees were affected by fireblight. Fireblight usually attacks a stem and kills it, but if the disease enters through blossoms in spring, you may see localized infections and leaf drop. If you see problems redeveloping this spring, it may help to take a sample to your local Extension office for identification of the problem.