Hello,

This could be fireblight, a common disease of pears. 

https://extension.colostate.edu/topic-areas/yard-garden/fire-blight-2-907/

Or it could be from too much or too little water. Trees need extra water when rainfall is lacking for more than 10-14 days. The younger the tree, the more susceptible to drought it is due to having a smaller root system. But mature trees can suffer from drought, too.

You may send branch samples with live and brown leaves, and fruits attached to MSU Plant Diagnostic lab. Include a picture of the whole tree, and some of the branches showing the problem. The diagnosis will include actions you can take for the condition they find. See the fee schedule and instructions here- 

https://www.canr.msu.edu/pestid/

Or, you can hire a certified arborist, a professional who has taken training in care, diseases, pests and passed certification tests. He/she will come on site and give a complete diagnosis and a plant care plan. If any corrections( pruning aerating, etc)  to the trees are needed, the arborist can perform them. Find certified arborists by zip code here—-

www.treesaregood.org

Check your soil around the tree to a depth of 10-12 inches. Use a narrow trowel or shovel and dig carefully somas not to cut or injure large roots. If soil is dry, water the tree all the way around the root zone until this depth is moist. If it is wet, or sticky heavy soil, the roots may be drowning, and you will need to determine why too much water is standing around the roots.

I hope this is helpful. Thanks for using our service.