Sam:

Sunburn is not the culprit. That would not turn the leaves black. More likely it is the pear psylla, a tiny fly that lays eggs all over the tree. Once the eggs hatch, the instars secrete a honeydew that is in turn colonized by fungus. It is this fungus that usually turns pear leaves black.

The best solution I have found is a couple of very thorough dormant sprays with horticultural oil, mixed at about 6-8 ounces per gallon. The overwintering eggs will be present in all the little cracks and crevices of the tree, so careful coverage is important to break the pear psylla life cycle.

I would recommend you time these dormant sprays once in early winter, and again just before bud break. Once the psylla cycle has begun, it is nearly impossible to eliminate the psylla instars with growing season sprays, and fungicides are impotent against the black sooty material on the leaves.

Don Yellman, Great Falls, VA

If you could post a picture that would be helpful. The problem you describe could be Pearleaf Blister Mites. Although they tend to give a speckled appearance, in heavy infestations the leaves can turn almost entirely black. I have this problem badly on some of my trees and it's no fun whatsoever. I would doubt this was the problem if the black decoloration is solid and not speckled or grainy. In any case, pictures help diagnosis.