Q.Pear bud turning black in spring
Why are most of the pear buds turning black and falling off the tree in early spring? Only 5% grow to full pear size. The tree is about 50 to 70 years old. The developed pear has a rough grey skin.
This sounds like a Fire Blight on the Pear Tree.
Here are some articles that will give you more information.
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7414.html
https://www.gardeningknowhow.com/edible/fruits/pear/pears-and-fire-blight.htm
https://www.gardeningknowhow.com/plant-problems/disease/fire-blight-remedies-and-symptoms.htm
https://www.gardeningknowhow.com/edible/fruits/pear/fixing-pear-tree-problems.htm