Question
I live in southern middle Tennessee. I have two pecan trees that are 20 years old. They seem to bloom and pollinate, but seldom have but a few nuts. Three years ago there were several nuts, but lately all the small nuts drop early except for a few that are now turning black and falling off the tree.

Answer
From the discription I am not really sure. I would suggest you call your local Extension Service office and them for help. Here is a web link that discribes the major problems that pecan can have. And a link to the contact page of the Tenn. Extension Service

http://muextension.missouri.edu/xplor/miscpubs/mp0711.htm

http://www.utextension.utk.edu/offices/default.asp