||Economic analysis of management alternatives for rangeland grasshoppers is critical for development of an integrated pest management program for western US rangeland. Such an analysis depends on estimating forage availability for a broad range of conditions. A computer model that (i) can run on a microcomputer, (ii) simulates forage growth as a function of weather, (iii) allows for removal of forage by grasshoppers or domestic livestock, and (iv) requires only minimal input data can be used for this purpose. Therefore, a simple simulation model of rangeland forage production on the northern Great Plains (RangeMod) was developed as a tool for management of rangeland grasshopper populations, The model is driven primarily by daily precipitation. Temperature is used to initiate growth in the spring and determine physiological maturity toward the end of the growing season. A simple algorithm was developed to simulate soil-water relations. Capability is provided to generate precipitation (events from a uniform distribution) based on user defined parameters. In addition, site-specific parameters (provided by a user) are used to adjust RangeMod to local conditions. Therefore,RangeMod can be used on a microcomputer to simulate rangeland forage growth over a broad range of conditions where detailed environmental data are not available. RangeMod was verified by testing responses to temperature, precipitation, and herbivory. Generally, simulation results were very sensitive to the soil moisture parameters. RangeMod has been linked to a grasshopper population model and economic analysis as part of a decision support system for rangeland grasshopper management.