Yellow spot on pears
How to cure or prevent yellow spot on pear trees
Are you talking about Pear Rust?
I check the tree every couple of days and pick off all affected leaves and bag and bin them.
The rust has a complex life-cycle, part of which takes place on Junipers ... since our neighbour cut down her juniper tree we've had less rust on our pear.
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.