Based on what can I see in your picture, your Bradford pear has lichen on its trunk. Lichens are living organisms composed of a fungus and algae living in a symbiotic relationship. Lichens grow harmlessly on tree trunks and no control is necessary. Lichen tends to appear on tree trunks as the trees age and growth slows.
If you feel that there are other disease issues going on the the tree, feel free to contact me at the Jessamine County Extension Office at (859) 885-4811.