The Pesticide Orchard Ecosystem Model (POEM) is a mathematical model of organophosphate pesticide movement in an apple orchard ecosystem. In addition submodels on invertebrate population dynamics are included. The fate model allows the user to select the pesticide, its application rate and general orchard maintenance. The pesticide is assumed to only move downward from the site of application. The model accounts for the effects of airborne losses, chemical binding, moisture movement and non-rain chemical movement. Extensive reparamaterization of the model's many submodels is allowed. Output is formatted as mass of chemical in major ecosystem components daily for up to ten years...Software Description: The program is written in the Fortran programming language for implementation on a Cyber 750 computer using the MSU Hustler 2 ver. 52.03 operating system.