Hello,

What you are seeing is pear leaf rust gall.

It is caused by a combination of a little insect blistering the developing leaves of the tree and laying their eggs, as well as a related rust disease.

The insects usually don't cause any damage.  It's just makes the tree look bad.

This problem might be related to variety susceptibility, all this rain we have had to date, this past years mild winter and the exceptional high rates of humidity.

Variety of pear that you have?

There is not too much you can do at this time for it.  Hopefully most of the leaves will naturally fall off.

An application or two of a copper fungicide sprayed soon after these rain events stop, as well as again in the fall when the leaves turn color and start dropping, may minimize this from occurring next year.

Always read and follow label instructions.

Sincerely,

David Rodriguez -Extension Horticulturist
Texas A&M AgriLife Extension Service
Bexar County