Fabraea leaf spot, also known as leaf blight and black spot, is caused by the fungus Fabraea maculata. This disease usually appears late in the growing season but can occasionally develop in late May and early June. Fabraea leaf spot attacks leaves, fruit, and twigs of pear.
Look for a suitable fungicide.

I would also have a look at Fireblight, when the leaves turn black. There is some gen at https://gardenfocused.co.uk/fruitarticles/pest-disease/fireblight.php.