CALEX is a microcomputer based shell program developed to provide management assistance to farmers. The shell, which is implemented in conjunction with modules specific to a crop, consists of two separate programs: an executive, written in C, and an expert system shell, written in Lisp. The executive serves as the interface to the user, to a resident plant growth model, and to the disk, The expert system makes the actual management decisions. Initial development of the program has focused on the development of a package of modules for California cotton.