Answer: I would suggest you read the label for the product you used and see if it was listed for use on pear trees and for the pest you were trying to control. If not, then this may have caused the problem you are seeing now. Please contact the manufacturer for information about their product and its use. Their web site includes customer service contact information.
It is also possible that you are seeing a disease problem such as fireblight on your tree. You may want to consult with your local county extension to try to obtain a more specific diagnosis of the problem(s) affecting your tree and based on knowing that, they can help you decide how to proceed.
Good luck with your tree.
Q&A Library Searching Tips