Possible Diseased Bradford Pear
brown spots on leaves of a bradford pear. This spring leaves falling off tree
Please help me determine problem with tree?
Oklahoma County Oklahoma
We will need pictures to determine the exact cause. However, the most common fungal disease we have seen this spring is pear rust, with symptoms of brown to orange and yellow spots on the leaves. Here is a link to a document explaining rust diseases - http://entoplp.okstate.edu/pddl/2013/PA12-8.pdf/view?searchterm=rust.
Essentially there is nothing you can do now that the disease is present. Control is preventative so next spring you should be prepared to spray with a fungicide to control the disease if desired. In general the disease is not harmful to ornamental pears, just a nuisance and generally doesn't warrant control. Rust diseases have an alternate host, the juniper, usually the eastern redcedar. When you see the bright orange galls developing in the spring during wet, mild weather, that is the time to spray your pears with an appropriate fungicide labeled to control rust. Gathering fallen leaves and destroying them can also be helpful in reducing the spread of the disease.