Software for learning about the benefits of site-specific weed management compared to a uniform herbicide application. No GIS software is needed. The benefits are predicted from weed maps drawn by the user. Herbicide use may be reduced 30 to 80% without impacting crop yield with site-specific weed management. Herbicide use is varied within a field to match the variation in the weed population. However, it is not always clear that the reduction in herbicide and other benefits of site-specific weed management will justify the cost and that future weed control will not be compromised. The outcomes of site-specific weed management vary with the composition and spatial distribution of the weed population, possible herbicide treatments and the resolution of variable management. WeedSite software was developed for predicting the benefits of postemergence site-specific weed management in irrigated corn and how the benefits vary with the weed population and the approach for variable herbicide application. Georeferenced weed maps and GIS software are not needed. Net gain from site-specific weed management, area of the field not treated, herbicide use and cost, yield loss from weed competition, and weeds left in the field are all calculated from hand drawn weed maps. Results can be mapped. WeedSite is useful for educating growers, agricultural consultants and students about the potential benefits of postemergence site-specific weed management because predictions are consistent with what is known about the variation in the benefits of site-specific weed management. Also, users specify the distribution of weeds in a field, so the results may be more relevant to them than information from research studies. The installation package includes a user's manual.